Re: [time-nuts] Re. DIY atomic "resonator"

[David I. Emery]

On Wed, Apr 12, 2017 at 11:18:00AM -0700, jimlux wrote:
> Yep.  There's been a fair amount of work over the past decades on using 
> modulated reflectors for measuring antenna patterns (e.g. on phased 
> arrays).  You can have a diode/dipole suspended by resistive leads (with 
> an impedance of 377 ohms/square that are invisible) and turn it on and off.
> 
> Bolomey (I think) had an array of modulated reflectors, so you could 
> measure multiple points in the near field at the same time, and only 
> need to scan in one dimension. I can't remember if the reflectors were 
> modulated at different rates or with PN codes - either would work to 
> separate the responses.

In case some of you have not followed the Snowden (and related)
revelations about CSS/NSA/CIA snooping technology, apparently modulated
reflectors (corner reflectors with diode switches) are a standard trick
for ex-filtrating digital data streams from PCs and displays and the like
and have been used upwards into the Gigabit per second area...

Interesting to hear about using them for probing antenna
patterns...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Satellite TV messed up, how is GPS time

[David I. Emery]

On Fri, Nov 04, 2016 at 06:53:53PM -0500, David wrote:
> On Fri, 4 Nov 2016 18:43:03 -0400, you wrote:
> 
> >...
> >
> > There HAVE been attempts to deliberately jam cable distribution
> >satellites... mostly the EIRPs used for distribution signal uplinks
> >make this a bit difficult, but it has been done.   There are also some
> >countermeasures in place to help quickly locate and ID rogue uplinks.
> >
> >...
> 
> Captain Midnight was the first satellite incident that came to mind
> but I wonder how many others there have been.

I've heard various numbers (not all that many in NA, more in
other parts of the world) but as you may or may not know, orders of
magnitude more cases of accidental lighting up an uplink pointing at the
wrong satellite, or on the wrong transponder or polarity (or with the
polarity skew wrong) or at the wrong time.

There is a current upgrade in process to require most uplinks to
carry a DSSS spread spectrum buried carrier ID under the actual
modulation energy  with information in it that can be linked back to an
uplinker phone number and ID and location, either by directly including
that info or by an uplinker ID ESN listed in a protected non public
database kept by the satellite operators and space managers allowing them to
determine who the uplinker is (among their customers).


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Satellite TV messed up, how is GPS time

[David I. Emery]

On Fri, Nov 04, 2016 at 06:19:13PM -0400, David I. Emery wrote:
>   Solar outages are not greatly worse on C band.
> 
>   It WAS true that EIRPs at C band were kept lower at one time (to
> protect the now mostly completely abandoned terrestrial C band microwave
> telephone network which shares 3.7-4.2 Ghz with C band satellite) than
> at Ku band, but that is less true today...

Since folks have brought this up, a couple of more observations
are relevant.

C band has MUCH less weather absorption by normal storms...

Ku band satellite signal fades from rain in passing
thunderstorms often can and do exceed 10-12 db...

This means in practice that C band link budgets can get by with
significantly lower margin to handle rain fades...

So many Ku signals are run with big margins of excess signal so
as to reduce the number of seconds of reception lost to passing
thunderstorms  something not needed as much for C band.

Thus a C band dish sized to just work reliably will have less
margin for the noise floor to rise as the sun goes past the satellite.  
But it DOES rise for Ku dishes as well, just they may be sized to have
more margin and/or the satellite power is higher.

Some home DTH dishes don't leave much margin, others are better.

But it is not true that the sky noise temp doesn't go up a lot 
at Ku band during sun outage season or that for some dishes and some signals
this will not eat the margin up and "ku does not have sun outages".


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Satellite TV messed up, how is GPS time

[David I. Emery]

On Fri, Nov 04, 2016 at 03:19:20PM -0700, Hal Murray wrote:
> 
> petervince1...@gmail.com said:
> > Sorry Don, I beg to differ.  The effects are often not noticeable in these
> > days of digital television, but the noise-floor can definitely be seen to
> > rise dramatically on a spectrum analyser. 
> 
> Right.  But I think that's because the sun is lining up with the satellite 
> rather than the ionosphere is getting trashed and messing up propagation.

BOTH can be issues.   Faraday rotation can reduce polarization 
isolation in geomagnetic storms... worse at high latitudes... and also
geomagnetic storms can cause antenna pointing issues for satellites...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Satellite TV messed up, how is GPS time

[David I. Emery]

On Fri, Nov 04, 2016 at 09:58:50PM +, Mark Sims wrote:

> I was a local electronics parts store this afternoon and they were
> saying some of the satellite TV internet infrastructure was being
> DDoS'd...  ah, the subtle wonders of a few hundred thousand hacked TV
> cameras yammering down your pipe at the same time.

Interesting but probably not that likely.

At least DirecTV is fully capable of doing most things without
any Internet connection at all... maybe not Pay per view or special
stuff like the Sunday Ticket authorizations and data feed (or obviously
video on demand) ... but most everything else

There ARE lots of feeds of local stations to the uplink
facilities via leased fiber circuits, but I don't think a lot of those
are competing for bandwidth on the open Internet but are closed circuit
switched networks.   There is talk of using VPNs over the Internet but I
think such issues as DDOS attacks have mostly kept that from happening
just yet.

Most of the cable channels reach the uplink facility via C band
dishes from the cable signal distributions that feed other head ends... 

There HAVE been attempts to deliberately jam cable distribution
satellites... mostly the EIRPs used for distribution signal uplinks
make this a bit difficult, but it has been done.   There are also some
countermeasures in place to help quickly locate and ID rogue uplinks.

Because the US military and government is a heavy user of 
commercial satellite capacity, they maintain monitoring facilities that
keep constant watch for intruders... as do the satellite control
facilities responsible for the operation of the birds.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Satellite TV messed up, how is GPS time

[David I. Emery]

On Fri, Nov 04, 2016 at 06:11:48PM -0400, David I. Emery wrote:
> 
>   The solar outage season (a loss of signal for about 10 minutes
> max when the sun is directly behind the satellite as seen from the dish)
> runs from very late Sept (deep south) to about Oct 15 or so (Canada).

Try 
<http://www.satellite-calculations.com/Satellite/suninterference.php>



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Satellite TV messed up, how is GPS time

[David I. Emery]

On Fri, Nov 04, 2016 at 05:51:35PM -0400, Don Murray via time-nuts wrote:
> DirecTV and DishNetwork are on Ku-Band platforms.
> Ku-Band is not affected by sun outage.

I beg to differ !!!

The sun is still plenty energetic enough at 10-12 Ghz to
override weak satellite transmissions.   

In fact the solar flux is measured at 10 Ghz...

Solar outages are not greatly worse on C band.

It WAS true that EIRPs at C band were kept lower at one time (to
protect the now mostly completely abandoned terrestrial C band microwave
telephone network which shares 3.7-4.2 Ghz with C band satellite) than
at Ku band, but that is less true today...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Satellite TV messed up, how is GPS time

[David I. Emery]

On Fri, Nov 04, 2016 at 04:52:25PM -0400, paul swed wrote:
> U with respect to direct TV is it the noramal two time per year sun
> outage its about the right time.
> Regards
> Paul.

Nope way off...

The solar outage season (a loss of signal for about 10 minutes
max when the sun is directly behind the satellite as seen from the dish)
runs from very late Sept (deep south) to about Oct 15 or so (Canada).

Around here in Boston the max is either the 9th or 10th of October
depending on which satellite you are talking about.   Both DirecTV and
dish use more than one orbital location so there are outages of DIFFERENT
channels at different times during the outage seasons in spring and fall.
This of course somewhat depends on the level of service you have, such
as whether you get the entire HD package or International channels or
your local TV stations, and what market area you are located in.

Some outage happens for a window of maybe 4-6 days centered on
the max... but because of the cliff effect with FEC corrected digital
modulations that means that reception will be close to perfect until the
S/N gets just a little worse and then it fails completely - this may
almost not be noticeable except when the sun is right behind the
satellite.



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Visiting Greenwich

[David I. Emery]

On Tue, Jul 05, 2016 at 10:20:14PM -0400, David I. Emery wrote:
> 
>   I might add I have been to Bletchly park myself but have been
> waiting for a return visit with my son (who will graduate with a CS degree
> in a year - and a biochem degree) rather than take my wife who really
> isn't all that into what it means...

Apologies... meant for a friend... not the list...


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Visiting Greenwich

[David I. Emery]

I might add I have been to Bletchly park myself but have been
waiting for a return visit with my son (who will graduate with a CS degree
in a year - and a biochem degree) rather than take my wife who really
isn't all that into what it means...




On Tue, Jul 05, 2016 at 12:18:59PM -0400, William H. Fite wrote:
> I second the motion, John, re Bletchley Park. My spouse is a quantum
> information theorist (sort of a cross between a quantum physicist and a
> theoretical mathematician) who develops algorithms that crypto people then
> adapt for practical use. Mostly for quantum crypto. Both of us found
> Bletchley absolutely fascinating. That was a couple of years ago and we
> found several enthusiastic volunteers including one who was a pretty fair
> mathematician.
> 
> On Tue, Jul 5, 2016 at 8:10 AM, John Ackermann N8UR  wrote:
> 
> > I'm a bit of a crypto-geek and was able to visit Bletchley a couple of
> > times, again many years ago.  It is definitely worth a trip, though from
> > what I saw on my visits and have read lately it has evolved badly.
> >
> > It used to be run on a shoestring with enthusiastic volunteers everywhere
> > and lots of eccentric touches.  There were local craft clubs who set up on
> > their niche historical displays on the weekends, there was a guy who'd
> > taken over the front room of the manor with his huge Churchill memorabilia
> > collection, and though things weren't fancy they were lots of fun.  Over
> > the years, though, the site has been "corporatized" and while the exhibits
> > have gotten fancier, some of the fun has gone away, and a lot of the
> > passionate volunteers seem to have given up.
> >
> > My last visit was years ago, though, and I hope that what I've read about
> > what's happened since is overstated.
> >
> > John
> >
> >
> > On 7/4/2016 10:01 PM, Bob wrote:
> >
> >> Hi Dave,
> >>
> >> Yes, as many mentioned all the clocks are up the hill at the Observatory,
> >> and very much worth the trip.  As you mention you are with your family, I
> >> would like to add that yes I did cajole my family to the NMM and the
> >> Observatory, but also to Bletchley Park (just a short train ride outside
> >> London) and Bletchley Park was easily the most memorable.  There are
> >> wonderful volunteer guides, and many interesting devices that you can get
> >> up close to.  Bletchley was more like visiting a working lab than a
> >> museum.  I think every time nut would enjoy Bletchley quite a bit.
> >>
> >> https://www.bletchleypark.org.uk/ 
> >>
> >> Cheers,
> >>
> >> Bob
> >>
> >> On Jul 4, 2016, at 6:31 PM, Dave Martindale 
> >>> wrote:
> >>>
> >>> I am in London England at the moment, playing tourist with the rest of my
> >>> family.  I want one day to be a visit to the National Maritime Museum at
> >>> Greenwich, which includes the Royal Observatory Greenwich.  I am
> >>> particularly interested in seeing Harrison's H1 through H4, plus other
> >>> high-precision mechanical timekeepers (pendulum clocks, etc).
> >>>
> >>> I know they are at the NMM - their web site shows some of them.  But
> >>> where
> >>> are they located on the site?  The NMM has a large main building down
> >>> near
> >>> the Thames, while the Royal Observatory and related buildings are on the
> >>> top of a hill further inland in Greenwich Park.  Are the chronometers and
> >>> other precision timekeepers on display somewhere in the Royal
> >>> Observatory,
> >>> or down in the main NMM building?  I've spent an hour or two browsing web
> >>> sites without finding this particular bit of information.
> >>>
> >>> I figure there must be list members who have visited the NMM, and know
> >>> where the precision timekeepers are actually displayed.
> >>>
> >>> Thanks,
> >>> Dave
> >>> ___
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> >>>
> >>
> >> ___
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> >>
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> >
> 
> 
> 
> -- 
> Mundus vult decipi.
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-- 
  Dave E

Re: [time-nuts] iGPS?

[David I. Emery]

On Mon, May 18, 2015 at 09:52:03PM -0700, Jim Lux wrote:

> Why iridium?  Why not Sirius or XM or DBS. Unless you want something 
> world wide, as opposed to "populated areas served by broadcast radio and 
> TV"

Well it seems to me I remember Iridium is time domain duplex
around 1610 MHz or thereabouts... which isn't too far from the L1
civilian GPS at 1575.42 and quite possibly inside the bandwidth of
some civilian L1 LNAs and antennas.

Sirius XM is not that close at 2320-2345 Mhz.

And inside its spot beam the Iridium signal is quite a bit more
powerful and coming at one from constantly changing angles... whilst 
the Sirius XM birds are either geosync or in Molninya orbits and don't
move much over short intervals - as does an Iridium signal.

And of course (for the military especially) it IS worldwide and
not just restricted to NA (where such an anti-jam capability is less 
useful at least at the moment).  Something that works world wide
is of course what the military folks need.

And I suspect timing can be derived from the satellites TDD
and message timing pretty easily if that is accurately synced to some
reference...

Others more familiar with the details may comment here...

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Lucent KS-24361 10 Mhz out success.

[David I. Emery]

On Wed, Dec 03, 2014 at 08:46:58PM -0500, Bob Camp wrote:

> > But it seems that Morion rulez, noise-wise.
> 
> The OCXO in the TBolt beats the Morion parts by a wide margin.

That implies all Tbolts have the same OCXO... is that actually
true of most of the surplus ones ?   Weren't there varients in
some of the early lots at least ?

And there certainly were widely different date codes...

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Convert Stanford Research SR620 time-interval counter to SR625 ???

[David I. Emery]

On Wed, Dec 03, 2014 at 02:53:50PM -0500, Paul wrote:
> On Wed, Dec 3, 2014 at 12:08 PM, Neil Schroeder  wrote:
> 
> > I haven't really ever been able to talk to my
> > prs10 via serial
> >
> 
> I took the easy way out and bought the interface board (directly from SRS).

Do you have any rough number as to what they charged you for
this ?   



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] NAA experiments as a reference

[David I. Emery]

On Sun, Sep 14, 2014 at 10:20:48AM -0400, paul swed wrote:

> I still do not see why if I offset the LO to -150 hz I get a useful display
> to judge timing. I am using the lissajous method.

Consider that with the LO offset 150 Hz you will have a 100 Hz
beat note with the mark tone and a 200 hz beat note with the space
tone - more or less exactly right on if the MSK signal carrier is right
on (which it is) and the signal is true MSK (which is is) and the 150
Hz LO is nearly right on (which it presumably is).

And the 200 Hz and 100 Hz are of course related and coherent
with each other (the phase of the mark and space tones is precisely
related to each other because of the nature of true MSK).

This means the resultant waveform should be stable seen in
a sweep triggered by your local clock at 100 Hz and also in a lissajous
pattern with the LO.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] MH370 Doppler

[David I. Emery]

On Tue, Aug 19, 2014 at 12:08:24PM -0400, Joe Leikhim wrote:
> My understanding is that the BFO and BTO values are self reported from the 
> SDU (Terminal in the aircraft) and they represent adjustments made by the 
> SDU. If so the BFO value would be the AFC adjustment relative to the OCXO 
> onboard. My contention is that if the investigators are assuming the OCXO 
> is 2Hz high and reporting an +88Hz offset as 86Hz Doppler, what if in fact 
> the OCXO is 10Hz high? Then the doppler is 78Hz and that means the velocity 
> and location at each of the pings is way off.

Clearly they have a history of the MH370 Aero Clasic terminal
measured burst frequency at the ground earth station and the BFO value
the SDU reports it used WHEN the aircraft was on the ground before it
took off and WHEN it was being tracked by radar/mode-s/ads-b and was in
a known position going at a known velocity on a known heading.This
should presumably allow determination of the baseline OCXO long term
error, and some indication of its short term drift as well.

Whether that particular SDU attempts to use any form of EFC of
its OCXO based on measured satellite L band downlink frequency error
corrected for doppler or not I do not know.   It is quite possible  that
any correction for OCXO error is just a value factored into computing
the BFO to use and not used for actually correcting the standard with a
EFC DAC.

If that is true then the drift should be presumably be pretty
typical of the class of OCXO used in the SDU which I suspect should be
fairly small once it warms up - over a 6-8 hour period after warmup.
And there may be some history of that particular terminal from previous
flights to validate this.

Of course if environment significantly changes the drift
performance of that particular OCXO it is possible that temperature, or
pressure or power conditions were so different on the fatal flight that
the drift might be larger and unknown in character... not sure.  It is
an error to consider of course.   Not clear to me how carefully it has
been or what possible factors have been considered.   But surely the
folks doing the analysis know about these issues.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] MH370 Doppler

[David I. Emery]

On Mon, Aug 18, 2014 at 04:18:30PM -0400, Brian, WA1ZMS wrote:

> I thought that Inmarsat terminals had AFC to the sat's down-link.  Not
> to the degree of true phase-lock like DSN has but enough so that the
> sat's abillity to do doppler correction on the uplink is valid to help
> with BER, etc... Otherwise the doppler correction would be of no help
> and not be needed.

I beleive most Aero Classic terminals use a fairly good
OCXO.   Somewhere I may have a limit spec on stability, but those
docs are not immediately handy.

Normally a demod in the terminal is kept tuned to one of the
continuous L band control channels which I believe may be Doppler
compensated in the ground uplink transmitter for the 6 Ghz C band uplink
Doppler and LO drift on the satellite so it is correctly on frequency as
radiated on the L band downlink.   This could supply a frequency
reference to the terminal that could be used to AFC the terminal
frequency standard so it is close to right on.   Doing this would
require terminal firmware to determine estimated Doppler at the L band
control channel downlink frequency from the satellite based on some
estimate of the planes position, satellite position and relative
velocities.

The QPSK DSP modems used at both ends would be easily able to
supply estimated frequency offset, both on the ground at ground earth
station and in the plane. It is presumably true that this measurement is
corrected on the ground end for the Doppler due to movement of the
satellite relative to the ground station on the C band downlink relaying
the L band uplinks from the plane so it reflects frequency error as seen
at the satellite on the L band uplink with the downlink and satellite LO
drift terms removed.   I presume this is what INMARSAT is reporting, but
am not sure.

IIRC the plane is expected to adjust its burst uplink frequency
and timing to come out right at the satellite receive antenna... thus 
compensating for the uplink Doppler at L band and the time delay too.
But I do remember that the ground supplies feedback on the control
channel as to how much the plane is off so it can adjust...

Guess it might be time to dig out the docs again.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Cutler NAA on 24.0kHz....

[David I. Emery]

On Fri, Aug 15, 2014 at 03:39:07PM -0700, Pete Lancashire wrote:
> URL ok from here

The text of the original post had "*"s in the URL... which
didn't work so well...

Partly pilot error here...

Works OK without the "*"s



> 
> -pete


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  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
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Re: [time-nuts] Cutler NAA on 24.0kHz....

[David I. Emery]

On Fri, Aug 15, 2014 at 04:56:01PM -0400, paul swed wrote:
> Yes I can see on page 2 of the pdf thats the trick. Its a non costas loop
> trick.

That PDF is returning a 404 for me at the moment...



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02493
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Re: [time-nuts] Cutler NAA on 24.0kHz....

[David I. Emery]

On Fri, Aug 15, 2014 at 04:56:01PM -0400, paul swed wrote:
> Yes I can see on page 2 of the pdf thats the trick. Its a non costas loop
> trick.
> "The action of the MSK card doubles the phase shift".
> So it is the classic double the frequency stateless carrier recovery. that
> may drop phase due to noise.

Needless to say one can track the recovered carrier with a very
narrow loop which will not slip in phase easily during a fade.

I believe you found that simply using it to clock a flip flop
wasn't reliable... but a narrow carrier tracking loop tracking it would
be...


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  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
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Re: [time-nuts] Cutler NAA on 24.0kHz....

[David I. Emery]

On Fri, Aug 15, 2014 at 03:09:23PM -0400, paul swed wrote:

> I had discounted it because of the lack of info and totally unclear how to
> get rid of the FSK. MSK is FSK just with a very narrow shift. Also the
> effects of the fsk on the carrier. Hmmm glad I am typing this.
> It may be that the mark or the space is indeed exactly the true carrier and
> that op amp circuit is notching out the shifted carrier. I will bet thats
> the trick!


MSK is a kind of continuous phase differentially coded PSK in
which the carrier phase smoothly shifts either EXACTLY plus 90 degrees
or EXACTLY minus 90 degrees in EXACTLY one symbol time - in the MSK
variety of PSK the transmitted carrier phase never stays the same as the
it was the last symbol time.   When transmitting steady mark there are a
series of these shifts plus 90 degrees (hi frequency mark) one after the
other, and when transmitting steady space there is a series of minus 90
degree shifts.

Obviously a steady negative phase shift is what is produced by
a signal below a center "carrier" frequency and a steady positive
phase shift by one above that frequency.   Thus the isomorphism with
filtered FSK.

Effectively a QPSK (multi-arm Costas type) tracking loop should
be able to track a MSK signal just as if it was a filtered QPSK signal
with only 90 degree and minus 90 phase shifts each symbol time and generate
a phase continuous recovered carrier.





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  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
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celebration of what could have been, but wasn't and is not to be now either."

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[time-nuts] WWVB paper in May 2014 IEEE communications...

[David I. Emery]

Well the actual details of the WWVB modulation and time
codes are now published.

Was just leafing through some journals while doing some
boring system configuration here...

IEEE Communications Magazine May 2014 has a paper on page 210
by Yingsi Liang, Oren Eliezer, Dinesh Rajan, John Lowe

"WWVB Time Signal Broadcast Format and Multi Mode Receiver"

Seems to tell a lot more... 

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
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Re: [time-nuts] Airraft Ping Timing

[David I. Emery]

On Mon, Mar 24, 2014 at 06:15:57PM -0700, Chris Albertson wrote:
> Yes, word is that they were able to determine the Doppler shift in the
> plane's signal.  I'm surprised this was even recorded but it must have been
> in the satellite's telemetry downlink.   Projecting radial velocity and
> constraining it to be close to the earth's surface, I guess determines one
> path and the direction on it.


Perhaps some of the readers here are unaware that the INMARSAT
F3 in question is a bent pipe repeater in both directions.   It takes a
C band uplink from the ground and turns it around to L band, and turns L
band uplinks around to a C band downlink.

It has 8 spot beams, and one regional beam.   Channelization of
the uplink and downlink bandwidth and an board switch matrix allows 
various allocations of frequencies and bandwidth to the 9 beams varying
with load and demand.

There is no on satellite signal demodulation/modulation or
protocol processing  for the classic AERO signals to/from the plane ...
that is ALL done on ground at the GES (in Perth Australia AFAIK).

This would make it possible for INMARSAT (and others in the
region tasked with monitoring such things) to capture the actual
repeated RF from the plane and digitize it - this happens in the ground
equipment as part of the normal processing anyway - and dumping it to a
disk array somewhere is certain to be going on, either both inside
INMARSAT at the GES or at least at other (less public)  sites such as
Alice Springs.   The C band downlinks are global beams BTW and can
be received anywhere that sees the satellite.

As such the quality of the recovered Doppler and other signal
parameters is very much a function of the stability of the various LOs
(and sample clocks)  involved, which I believe can correctly be presumed
to be really high grade both in space and certainly on the ground. AES
(plane) timing and frequency may be less good, but it is more or less
locked to the L band downlink timing and frequency signals as reference.

The newer INMARSAT F4 birds do have DSP processing on the
satellite, but apparently NOT used for demodulating and processing the
various control channel signals on the satellite - but just for doing
beam forming and power allocation for the 120 spot beams these birds
support.   This of course would impact delay through the satellite
for precision timing and ranging.

But so far there are no reports that the F4 POR satellite was
involved. The high gain antennas on the AES (plane) are fairly
directional and if they were in use there might not be a lot of signal
seen on the POR bird.   Not sure if those pings would have been sent
via a low gain antenna on the AES, but I suspect normally not.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Aircraft ping timing

[David I. Emery]

On Wed, Mar 19, 2014 at 09:28:38PM -0700, nuts wrote:
> A lot of these satellites have "footprints" for each antenna. I don't
> know if the footprints are narrow enough to track a plane.

I do believe there is an time offset for each aircraft sent on
the forward control channel from the ground (which is shared with many
aircraft) that allows a particular  aircraft to transmit a frame in the
center of its allocated slot.   IIRC the ground measures the error and
sends a correction to the plane which allows the plane's transceiver to
compute just when - relative to the system frame timing derived from the
received forward control channel from the satellite  - it should
transmit the reverse control channel burst.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] WAAS.....

[David I. Emery]

On Wed, Jan 08, 2014 at 08:09:04PM -0500, Charles Steinmetz wrote:
> Nathaniel wrote:
> 
> >Following from that, suppose a jammer parks nearby and doesn't leave 
> >in a timely fashion. How long does it take for the FCC to swoop in 
> >(do they swoop? in my mind they do) and find the source?
> 
> One of my clients had exactly that problem with radar detectors in 
> parked cars interfering with its satellite earth stations.  In that 
> case, the answer was about three years.

Did the FCC actually DO anything about these things ?

I imagine there are some type acceptance issues that could
be invoked here...





> 
> Best regards,
> 
> Charles
> 
> 
> 
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  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
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'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
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Re: [time-nuts] How hard is it to detect a GPS Jammer?

[David I. Emery]

On Mon, Oct 07, 2013 at 11:30:57PM -0500, Bill Hawkins wrote:
> In general, we expect a jammer to be involved in criminal activity.
> 
> What about a wilderness guide whose reputation is built on finding
> the best spots to view Nature's wonders. Should he or she be happy
> to let people in the guided group save the coordinates of those
> spots in order to compete with the guide or avoid guide's services
> in the future?
> 
> Or would that be a justifiable use of jamming?

No.

Jamming can potentially impact a much wider area and safety of
life critical uses of GPS, and  very few wilderness guides are expert
enough to understand, control and mitigate this risk.   And even if one
particular one was, how is this to be reliably ensured ? Should  he or
she be licensed and certified and regulated as to how and when he might
jam safely - we don't current issue GPS denial licenses (except maybe to
LightSquared) ?

And even with someone suitably trained and licensed and
certified there is a balance between the slight risk that his jamming
harm something important or critical that society relies upon and his
own personal interest in denying GPS to his customers that I am not sure
we as a society have quite figured out.   Should private businesses be
allowed to deny GPS (or for that matter cellphone access) to folks
nearby or their customers - is this a legitimate interference with a
public resource ?

Obviously if the answer is yes, businesses should be allowed to
jam cellphones or GPS - then what are the limits - eventually all those
private jammers will make such services MUCH less useful - as they will
be unpredictably unreliable at apparently random times and places which
makes it very hard to trust them for anything important.   We will in
other words have allowed the private interests of certain folks to
destroy a commons, something we are getting increasingly good at BTW.

I suppose it is SOMEWHAT justified for a guide to search his
customers for GPSes, or have a strict policy of dropping them off at the
nearest road if they are found to be using one, or even to use a GPS
detector to ID GPSes in use... but an active attack seems wrong given
the risks involved.

And anything more nuanced in a policy on such invites various
low life scumbags to push the limits and use blatantly excessive power,
dangerous antenna locations, and generally horrid engineering that puts
important uses and users of the technology at serious risk for very
selfish personal reasons - perhaps in some cases just buying some cheapo
jammer instead of a proper licensed and limited one managed and
installed by someone who knows what he is doing.

Finally of course, who is to say that I cannot use my cellphone
for important messages - perhaps life critical (my wife is a doctor and
does this from time to time when she is on call)... or my GPS to locate
a store somewhere... perhaps if the jamming ONLY worked in a completely
private space owned or controlled by the jammer and not at all outside
of it would this begin to be marginally acceptable but it certainly
isn't in public spaces.  And I believe there should be mandatory readily
visible notices saying that jamming is use... allowing someone who 
truly needs access to know what is happening.

As for the wilderness case specifically there are any number of
strategies to defeat short range jamming of that sort - just announce
you have to "go" as the group leaves the scenic knoll and go back and
take a bearing (maybe automatically from a concealed GPS you already
have in you backpack) while peeing on the special rock...   Inverse
square law applies here of course... hard to radiate enough power to
deny over a long enough distance without being completely unsafe for
other users.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] How hard is it to detect a GPS Jammer?

[David I. Emery]

On Mon, Oct 07, 2013 at 08:02:13AM -0700, Jim Lux wrote:
> On 10/7/13 7:46 AM, Collins, Graham wrote:

> >The AMSAT Fun Cube Dongle is a very capable and interesting device.
> >Interestingly it uses the same Elonics E4000 front end chip that many
> >of the inexpensive DVB-T devices do. Apparently Elonics is no longer
> >in business and the inexpensive DVB-T devices using this chip are
> >becoming less common. The DVB-T devises using the R820T chip are
> >becoming the preferable versions when those with the E4000 cannot be
> >found. I wonder if the Fun Cube Dongle will be likewise changed
> >(perhaps it already has).
> >
> 
> This illustrates is the fundamental problem with leveraging cheap 
> consumer or government surplus gear.  The hacker community moves much 
> slower than the commercial one, so you wind up with projects requiring 
> things that are no longer sold.  It's particularly endemic in the 
> amateur radio community where we are always repurposing something that 
> hasn't been made for 30 years.  But it makes it hard for the new 
> entrant, who doesn't have a box full of old MASTR-II VHF radios or Bell 
> 202 modems or whatever sitting around.

This is also rather a sin of the marketing driven "innovation"
economy - product life cycles are so terribly short that by the time
someone spots a device that can be re-purposed in an interesting way it
is usually already EOL and unavailable in traditional new product
channels.

It takes time to do the reverse engineering (schematics, source
code, FPGA VHDL - what is that and why should we give it to you ?)  and
time to figure out how to re-purpose and make the thing work and usually
this is part time and one or two people and not a whole staff.  And then
there is time to write it up and publish articles and plans, and time
for folks to try it and discover it works...

But as many on this list know all too well, even in reasonably
well funded new product development the old story is "hey that is a
really neat chip that does just what I need" only to hear "Sorry too low
demand, or design or production problems, or ROHS or something, not
available in the future - or maybe just vaporware to assess interest and
never really available".   Or you design it in, the company is bought by
someone else, the chip abandoned and now YOUR product is EOL early.

> But the existence of that gear in some folks's garages tends to ossify 
> the development.  How many Bell 202 modems are still in use? But VHF 
> packet radio is 202 compatible, because every product made for the last 
> 30 years was compatible with the 202.  Not because it's inherently good, 
> but because you want to be compatible with the other people, and there's 
> a sort of rolling compatibility.

But that is not all bad, if you just need a modem that works.
Choosing something state of the art that DID NOT become a major defacto
standard (and there are dozens of examples in the modem world alone) 
means you only can expect to use the original device and maybe one or
two subsequent versions before it becomes unavailable and completely
obscure and rare and totally incompatible.   And then your design has to
be incompatibly upgraded with no backwards interoperability support
where if you had used some moldy oldy but goody you probably could buy
modern DSP based hardware that does that standard (you can for 202s)
among many other useful ones...and support both higher performance
and backwards compatibility modes at low cost and with high performance.

Obviously the problem then becomes convincing enough old pharte
holdouts to upgrade when it truly becomes a nightmare to support the old.
And that is not always easy.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] ***SPAM*** How hard is it to detect a GPS Jammer?

[David I. Emery]

On Sun, Oct 06, 2013 at 09:59:50PM -0700, Hal Murray wrote:

> Suppose I lived near a major highway.  Could I build a receiver that would 
> count jammers driving by?  Could I track them (at least somewhat) with a 
> directional antenna on a rotator?

I would think this would be a natural task for one of the SDR
setups like the USRP and gnuradio... and using the more sophisticated
MIMO versions of the USRP and a suitable DF antenna array of GPS
antennas you could use correlation interferometry to get a pretty good
bearing on a passing jammer (no mechanical rotating antenna needed).  
Use a couple of these in a suitable relationship to the road and you
probably could locate the vehicle in question and capture video of it.

Might be some quite interesting statistics near an interstate
with heavy truck traffic.



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Needed: The Real Serial USB Fix

[David I. Emery]

On Sun, Jan 27, 2013 at 06:47:07PM -0500, Peter Gottlieb wrote:
> What I would really like in Windows is a way to lock the configuration and 
> make it more of an appliance which always worked the same way.  That way a 
> small board talking to a Thunderbolt would always start up and just run.  I 
> suppose I need to get away from Windows and climb the Linux learning curve.

Yes, or become a Windows kernel maven.

It IS possible to figure some of this out, but Windows internally
is somewhat bizzare...

Linux is nice in that you can look at the code if it comes to
that (and if you are really desperate and willing to pay the price,
change it too)...


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Yb clock - NPR Story on Atomic Clocks

[David I. Emery]

On Fri, Aug 23, 2013 at 03:03:13PM -0700, John Miles wrote:
> Don't you just love paying to access research that your taxes already paid
> for?  Gives you a warm, fuzzy feeling all over. :-P

Now, now, perhaps it is better to feed the (GOP) pigs
than let them ban the research altogether as not conforming to
their simplistic world view...


> -- john, KE5FX
> Miles Design LLC


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  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
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Re: [time-nuts] More pictures of the mystery Collins Ru

[David I. Emery]

On Sun, Jul 28, 2013 at 07:54:47PM -0400, Bob Camp wrote:
> Hi
> 
> ….
> 
> There was a suitcase Rb that was used to sync up Have Quick's on the ground. 
> It was a Magnavox product rather than Collins. The idea was to get the radios 
> netted up without *anything* going over the air. Since the radios used 
> TCXO's, sync was fairly loose. I suspect that tightened up as they went 
> through the various versions ...
> 
> Bob
> 
> On Jul 28, 2013, at 6:58 PM, Brooke Clarke  wrote:
> 
> > Hi:
> > 
> > The military UHF voice radio scrambling depends on accurate time, hence the 
> > Have Quick (and follow on programs) time transfer standard.
> > Rb standards were used to maintain that time in the early days.

A minor quibble - HAVE QUICK is really not meant as a voice
"scrambling system" but an anti-jam ECCM technology.   If you hop around
every so often to a frequency that is unpredicatable (chosen by a
cryptographic random sequence) your opponent has to find and follow you
to jam you and do this fast enough to actually cause you problems.
Otherwise he is stuck with barrage jamming the entire band.

Hopping like this does require synchronized clocks... thus
the Rb... in order to hop at the right time to the right place.

There are several current and historic voice encryption systems
that provide strong voice security without hopping - lots of crypto
technology for that. But HAVE QUICK is often used with plain ole in the
clear AM voice and that voice can be reconstructed by having receivers
for each of the hop frequencies that vote on the strongest signal (or
some virtual equivalent of all of this done with FFTs and the like).

 Most cryptosystems do not depend on precise time of day,
though some antique ones did... 

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David I. Emery]

On Wed, Jul 10, 2013 at 07:40:50PM -0400, David I. Emery wrote:
> 
>   But if the satellite radiates what a local GPS package would and
> transmits ephmerides defining  its position and motion it could be
> included in a GPS solution and could be used for timing and frequency
> purposes the same as any other GPS satellite subject to whatever degree
> of relative accuracy the bent pipe clock obtains and the degree to which
> the ephemerides in the format transmitted allow an accurate position to
> be determined.
> 
>   And from what I have read it seems very likely the WAAS birds 
> meet these criteria..

Thinking some more about the bent pipe repeater aspect of
WAAS, aside from allowing any kind of WAAS like signal someone might
invent in the future to be retrofitted to existing satellites without
a long replacement cycle and expensive launches being involved - there
are some interesting properties of the design.

One is that one COULD bury in the WAAS uplink cryptographic
(eg essentially random to users not in possession of the key) spreading
sequence transmissions that would be radiated globally and could be
received with "unique" GPS hardware... such a covert channel in civilian
GPS could have various purposes... and would look rather noise like
to the rest of the world.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David I. Emery]

On Wed, Jul 10, 2013 at 07:45:39PM -0400, Bob Camp wrote:
> Hi
> 
> If the WAAS  birds are run in a fashion that gives a true GPS payload 
> performance, why not assign them a SN 32 or below and use them? 
> 
> If the WAAS birds are not in the "right numbers", why bother to set them up 
> and spend the bucks to make them behave like a nav sat? What's the payoff?


The patent cited here recently explains... for fixed timing
purposes and basic  anti jam a simple directional antenna pointed at the
WAAS bird allows rejection of many interferers without elaborate and
expensive active steered phased array nulling technology.   

And because - given a known fixed ground position - timing and
frequency can work with only one bird visible, this allows
timing/frequency using just the WAAS signal (or signals, they do provide
more than one WAAS frequency).

And potentially if the timing accuracy via the hosted payload is
respectable at least for the needs of many  fixed time/frequency users
this might supply a solution MUCH less resistant to local (nearby)
interferers than the usual more or less hemi pattern GPS antenna would -
as fixed dishes with considerable gain toward the satellite could be
used and in most places they would point well above the horizon and
could be shielded by nearby structures to further reduce jamming
susceptibility from jammers (intentional or unintentional) below or at
the horizon for the site.   For timing/frequency users (certainly an
important subset of the GPS user population) this provides some
protection by antenna pattern that is hard to obtain otherwise (and
users interested in higher precision or redundancy of timing could still
just use another GPS timing system based on normal hemi GPS antennas as
the primary - using the normal SVs - and rely on the dedicated dish
pointed at the WAAS bird only as backup in the event of jamming).

The choice of using different spreading codes from the normal
GPS set for WAAS or using a slightly different one is an overall system
architecture decision... which I guess was made in favor of not tying
up codes for regular SVs for the WAAS birds.   But AFAIK a receiver with
suitable firmware could still extract pseudo ranges and use them.

I guess there is an issue in any frequency translation scheme
with the relationship of carrier and code phase... a homodyne
distortion... due to the random phase of the LO(s)...  but this too can
be predistorted on the ground to come out right and that kept in line
via closed loop tracking of the downlink from a ground site.

I do understand that this insight into a potential further use
of WAAS beyond its use as a data channel and propagation beacon seems
to have happened later and not initially.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David I. Emery]

On Wed, Jul 10, 2013 at 02:42:19PM -0700, J. Forster wrote:
> David,
> 
> While I can easily see how you can do closed loop correctioin for Dopplar
> from the transmission point for a 'bent pipe' repeater, at any other
> location that correction would not be valid, because the paths are not
> parallel.

Sorry for my poor choice of words.   That is precisely what I
meant by "for an observer on the ground it is necessary to correct for
the satellite orbit induced doppler".This is true for ANY observer,
since it would seem certain that the closed loop correction actually is
structured and calculated to cause the satellite to radiate a carrier
(and timing modulation on it) equivalent to what an accurate  local GPS
satellite reference clock would generate if one was aboard the hosted
payload rather than on the ground.   Anything else would make no sense
as it is not incumbent on users to try to figure out ground relative
timing for some unknown uplink antenna somewhere.   And offsetting
radiated uplink time and frequency on the ground to make it right on the
satellite at the output of the bent pipe repeater is very feasible and
more or less a no brainer.

But if the satellite radiates what a local GPS package would and
transmits ephmerides defining  its position and motion it could be
included in a GPS solution and could be used for timing and frequency
purposes the same as any other GPS satellite subject to whatever degree
of relative accuracy the bent pipe clock obtains and the degree to which
the ephemerides in the format transmitted allow an accurate position to
be determined.

And from what I have read it seems very likely the WAAS birds 
meet these criteria..



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David I. Emery]

On Wed, Jul 10, 2013 at 08:10:45PM +0200, Magnus Danielson wrote:
> On 07/09/2013 04:25 AM, Joseph Gwinn wrote:
> >Yes, of course, but I don't think I explained very well.  The issue was
> >more economic than technical.
> >
> >There isn't much spare space, weight, or power in the birds, technology
> >moves rapidly, and the satellite companies don't want to have expensive
> >satellites that no longer generate rental income because something
> >became obsolete.  So they ruthlessly simplify.  A bent pipe will handle
> >any possible band-limited modulation, no matter if currently known or
> >not, and so is the safest solution.
> >
> >Now WAAS may have become important enough to command dedicated
> >hardware, but that came later, to the degree it came at all.
> 
> A bent pipe is more generic, but there are limits to how much you can 
> alter the output frequency too.

It seems completely inconceivable to me that either the antenna
system (particularly feeds) or transponder RF hardware on any commercial
Ku or C or Ka or X band satellite could possibly be frequency agile
enough to tune to 1575.42 MHz unless it was purpose designed to radiate
on that frequency from the start.

So any hosted WAAS payload is completely application specific.

What is not clear from anything I have read so far is whether
the UPLINK of the modulated WAAS signal is somewhere in the normal
(usually 6 GHz for C band satellites) uplink frequency band (probably
off one end or the other of the frequency range used).   Seems rather
likely that the ability to reuse the UPLINK common RF hardware
(reflector, feeds, filters, plumbing, maybe transponder front ends and
preamps) would make this a very natural design.

It also seems clear that doppler and bent pipe conversion 
oscillator correction is done closed loop by having the ground station
that generates the uplinked WAAS signal monitor the downlink from the
bird.Obviously correcting for the uplink doppler is a matter of
computation from knowing the bird's orbit orbit precisely, something
that would certainly be aided by constantly monitoring the range to the
bird from that WAAS uplink ground station and maybe another couple (for
ionospheric corrections).   Apparently the newer stuff uses two L band
frequencies to improve this (correct for plasma delay).   And the WAAS
signal of course allows continuous measurement of range accurately.

Correcting for a generally stable but slowly aging conversion
oscillator should be pretty straightforward as well, and presumably such
a closed loop system could hold the downlink frequency to rather tight
tolerances given a reasonably predictable stable oscillator on the bird.
The 240 ms up and back delay does make the loop a bit more complex, but
the bandwidth is very low I would think since the major perturbation is
probably thermal (satellite going into eclipse once a day at certain
times, and changes in sun angle over a day).

For an observer on the ground it is of course necessary to
correct for the satellite orbit induced doppler... which can be  up to a
couple of hundred Hz or more at 6 GHz - especially with inclined orbit
birds such as the INMARSATs.   The downlink carrier, while more stable
in frequency than GPS bird downlinks is hardly a highly accurate
frequency reference on its own.   But knowing the geo bird ephemeris
(which is broadcast on the WAAS) should allow  single signal time and
frequency solution for an observer at an accurately known location - by
correcting for bird movement.

How good the closed loops are relative to the precision clocks
on GPS satellites is an interesting question, there seems to be no
obvious design need to reach that level of stability... but it does not
seem impossible to get pretty close.   And much of what has been
achieved here seems related to a cost/power trade off in the hosted
payload in regards to its reference oscillator.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] WWVB remodulator for the Spectracom 8170...

[David I. Emery]

On Mon, Jun 17, 2013 at 09:35:51PM -0400, paul swed wrote:
> We as they say. I am most likely going to use a simple phase flipper.
> That preserves all of the Nist stuff and traceability and such. A flipper
> is simply a invert or non inverted signal and a switch. It is subject to
> propagation. But no more so than the original receivers.
> The remodulator gets rid of the carrier for time clocks.
> Both are actually reasonable to implement.
> Enough said other things to do.
> Paul

OK, clearly there is an advantage to that...

Does preserve the original carrier for traceability (sorta,
it does get inverted in phase from time to time)...


And the actual I channel of a Costas loop directly out of the I
double balanced mixer  should have a plus and minus signal one could low
pass filter and feed to a simple zero cross detector to control the
phase flip.   And if this is done by flipping carrier out of the TRF
stage via a DBM or analog switch and inverter it should preserve the AM
modulation on the original unless the TRF stage acts as  a limiter...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] WWVB remodulator for the Spectracom 8170...

[David I. Emery]

On Mon, Jun 17, 2013 at 06:11:15PM -0400, Bob Camp wrote:
> Hi
> 

> The Costas loop already has the AM component available. There's no
> need for a second receiver, just wire the AM output over to the output
> modulator.

That is standard for most Costas loops with an I arm... haven't
looked at his schematics carefully yet... possibly one might need some
kind of AGC to use it as input to  a second double balanced mixer
serving as modulator in order to get the right 14 (?) db AM as signal
fades slowly.   Not sure how deep the diurnal fades are...

But I guess if everything is quite linear over enough of a range
one could perhaps just remodulate without AGC and create a replica of
both the modulation and fades on  the local 60 KHz carrier.




> 
> Bob
> 
> On Jun 17, 2013, at 5:57 PM, "David I. Emery"  wrote:
> 
> > On Mon, Jun 17, 2013 at 02:41:13PM -0700, Burt I. Weiner wrote:
> >> Chris,
> >> 
> >> The 8170 was originally intended to be a frequency reference source 
> >> tied to the USFS (United Stated Frequency Standard).  It also gave 
> >> the time of day, but I believe that wasn't it's primary purpose.  As 
> >> I recall, there were some versions that did not have the clock 
> >> readout and some that had a chart recorder.  Back in the 80's I used 
> >> to drool (it was a disgusting sight!) over the Spectracom receivers 
> >> with the chart recorders.  At that time I was usuing a Gertsch RLF-1 
> >> with an external Moseley 680 chart recorder.  The remodulator 
> >> precludes it from being used as a frequency standard, but in my 
> >> opinion, so does the fact that WWVB is now phase shifted a bunch.
> >> 
> >> The 8170 uses a coherent detector and that's where the problem 
> >> lies.  While the 8170 still locks to the WWVB carrier, the new BPSK 
> >> scheme causes the detector to output bad data in spite of the 
> >> original dips in the carrier still being present.  I had always 
> >> wondered how it was able to pull the data out the noise, but never 
> >> had a manual until just recently.  I had naively assumed that the 
> >> WWVB new BPSK scheme would not affect the time of day aspect of the 
> >> 8170.  Like I said, I only use it as a clock in my shoppe, and being 
> >> an old dog I don't easily learn new tricks such as looking in a 
> >> different direction for one of the other clocks.
> > 
> > I suppose I am stating the obvious, but why not combine Paul
> > Swed's Costas loop and this scheme to output a phase locked 60 Khz 
> > with the right AM modulation ?
> > 
> > 
> > 
> > -- 
> >  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
> > 02493
> > "An empty zombie mind with a forlorn barely readable weatherbeaten
> > 'For Rent' sign still vainly flapping outside on the weed encrusted pole - 
> > in 
> > celebration of what could have been, but wasn't and is not to be now 
> > either."
> > 
> > ___
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> 
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-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] WWVB remodulator for the Spectracom 8170...

[David I. Emery]

On Mon, Jun 17, 2013 at 02:41:13PM -0700, Burt I. Weiner wrote:
> Chris,
> 
> The 8170 was originally intended to be a frequency reference source 
> tied to the USFS (United Stated Frequency Standard).  It also gave 
> the time of day, but I believe that wasn't it's primary purpose.  As 
> I recall, there were some versions that did not have the clock 
> readout and some that had a chart recorder.  Back in the 80's I used 
> to drool (it was a disgusting sight!) over the Spectracom receivers 
> with the chart recorders.  At that time I was usuing a Gertsch RLF-1 
> with an external Moseley 680 chart recorder.  The remodulator 
> precludes it from being used as a frequency standard, but in my 
> opinion, so does the fact that WWVB is now phase shifted a bunch.
> 
> The 8170 uses a coherent detector and that's where the problem 
> lies.  While the 8170 still locks to the WWVB carrier, the new BPSK 
> scheme causes the detector to output bad data in spite of the 
> original dips in the carrier still being present.  I had always 
> wondered how it was able to pull the data out the noise, but never 
> had a manual until just recently.  I had naively assumed that the 
> WWVB new BPSK scheme would not affect the time of day aspect of the 
> 8170.  Like I said, I only use it as a clock in my shoppe, and being 
> an old dog I don't easily learn new tricks such as looking in a 
> different direction for one of the other clocks.

I suppose I am stating the obvious, but why not combine Paul
Swed's Costas loop and this scheme to output a phase locked 60 Khz 
with the right AM modulation ?



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] OT: eBay Contact Congress

[David I. Emery]

On Mon, Apr 22, 2013 at 06:13:43AM -0700, J. Forster wrote:
> Hi,
> 
> I recieved a very odd communication, apparently from eBay, this morning.
> It is a request to contact Congress about sales taxes on internet sales.
> 
> It APPEARS to be genuine, but I'm unconvinced.
> 
> Has anybody else received this email, and is it for real?


I have received either two or three of these messages in
the past few days.   Headers do show they came from Ebay...

Some folks may support their position, others may not...

I'd rather buy stuff than be asked to lobby for them...

> 
> Puzzled,
> 
> -John
> 
> 
> 
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-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] UPDATE: DATUM 9390-52054 Grief again...

[David I. Emery]

On Sun, Apr 14, 2013 at 03:23:50PM +0200, Luciano Paramithiotti wrote:
> I have a 9390-53120. The 16.368 reference for the GPS is coming from a
> 4 pin (14 pin size ) oscillator on the GPS interface board.
> The other internal oscillator board mount a 1 MHz TCXO I never had
> seen locked to GPS.
> Normally I use it only for UTC time display.
> This GPS use an antenna with 50dB gain, so I have added a preamplifier
> to normalize its sensitivity.
> I had two fault in 10 year of life on the power supply board.

The 16.368 in mine is locked to the 10 Mhz (from a Rb in my
box) via a PLL.   The Rb is disciplined, but of course whether that
means locked or not is a matter of definition.   But pretty obviously
the amount a Rb moves is probably not enough to have any impact on
the time base to the GPS receiver at all.

That box (that I refered to) is off line and has been for while,
the DC to DC converter card died... and while I could fit a PS in there
I have been looking for another card to replace it.



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] UPDATE: DATUM 9390-52054 Grief again...

[David I. Emery]

On Fri, Apr 12, 2013 at 11:48:47AM -0700, Burt I. Weiner wrote:
> Sorry for the delay in posting this update.  Things have been hectic, 
> and then there was NAB.
> 
> Here's what I've discovered:  The receiver started working after 
> about 6 hours of just sitting.  However, the 9390's internal Vectron 
> oscillator was quite a ways off frequency and did not want to lock 
> after trying to stabilize all night.  I had to tweak the adjustment 
> screw quite a ways and then, after a while, it locked.  Prior to this 
> episode the oscillator had been sitting at only a few E-12.  I 
> suspect that this oscillator has had an intermittent problem for a 
> long time, and I should not have had to tweak it as far as it wanted 
> to go.  The receiver portion has not failed in the few weeks since it 
> decided to start seeing satellites again.  Maybe because I had 
> tweaked the oscillator?

I have an ancient 9390 that has an ancient Trimble GPS board in
it that takes a 16.368 reference synthesized from the 10 MHz standard in
a PLL loop with a VXCO. This is used in the L band downconversion... 
and for timing generally and given that is PLL derived from the 10 MHz
quite likely if the 10 MHz is significantly wrong the receiver won't
find satellites.   I remember I had to fix this PLL in my box before the
receiver in that box would lock up... initially the PLL wasn't locked,
but the 16.368 VCXO output WAS present  - so for that receiver it has to
be pretty close to right on to work.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Win XP and NIST time

[David I. Emery]

On Tue, Mar 26, 2013 at 07:39:51PM +0100, Alberto di Bene wrote:
> On 3/26/2013 7:21 PM, Dan Kemppainen wrote:
> 
> >Keep in mind, we are after all, taking about windows. An operating
> >system that IS NOT real time operating system. (You think it is, try
> >move a continuous stream of a few 6+ MBytes/Sec data to it!)
> 
> Well, the Perseus SDR, when set to its maximum sampling rate after the DDC, 
> sends
> the I and Q continuous streams (24 bit/sample each), to the PC at a rate of 
> 2 MHz. This
> means 12 MBytes/sec via a high speed USB2 port. Using one the many 
> available SDR
> programs, those 12 MBytes/sec are received, FIR and FFT are applied, 
> demodulation
> algorithms are used, and there are no glitches in the final audio...  if 
> even a single sample
> would be lost, you would ear immediately the artifact
> 
> Windows is not as bad as somebody would depict it... :-)

I have been using Windows for digital video analysis and
capture for years... often capture multiple 70-80 mb/s transport streams
by the hour from USB and PCI sources and output similar for testing.

It works.

Does take buffering and tuning in the code, and some in the
hardware.



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] LORAN C still on the air 24 hours SRS 700 looking good

[David I. Emery]

On Tue, Mar 19, 2013 at 01:29:44PM -0400, paul swed wrote:
> Peter you are in boston, I am in franklin. We must be 25-30 miles apart
> Regards
> Paul

Peter lives about 3 miles from my house in Weston... in
a corner of Natick abutting Weston.   So three of us are quite close.
John Forster lives in Belmont (or did)... which is also pretty close.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Using a frequency synthesizer replacement for motherboard oscillator

[David I. Emery]

On Fri, Nov 30, 2012 at 09:58:29PM -0500, Bob Camp wrote:
> Hi
> 

> The problem just the clock it's also the operating system. If it's not
> designed with timing in mind (= it's an RTOS at some level) then you
> will have sloppy timing. Counters can help, but they are not the entire
> solution. If your email (or anti-virus or ...) program can pop up and
> monopolize the cpu for a chunk of a second (as in 10's or 100's of ms), 
> precision timing isn't going to work very well. There's only so much you
> can do after the fact. If the pps edge was supposed to go out 27 ms ago,
> and you only got control back now, you are out of luck. 

No doubt that you get into a sort of philosophic meaning of 
what-really-is-now relativity here... if parts of the kernel know what
time it is quite precisely but other parts and most user programs are
only loosely aware of and only able to react to it post facto by large 
and jittery intervals, what is the meaning of microsecond or even ns
level OS time sync ?

Most modern kernels *internally* have at least some degree of
fairly serious real time high priority tight deadline stuff going on -
and API hooks for accessing it available - the degree to which this is
exposed and visible to or usable by user space threads varies a lot, and
correctly using this stuff always requires pretty deep skill and
thought.  Not for the faint of heart or inexperienced.   Very easy to
make subtle errors that cause bugs that happen only once every few
hundred or even many thousands of hours.

And pretty obviously the more control and access the user (eg
applications programmers) get and use the less likely it is that some
combination of separately developed and architected applications and a
particular kernel running on particular hardware will handle all of this
right ALL the time.   Emphasis here on ALL, it usually works most of the
time but making it essentially never fail is really really hard.  And
many of those failures result in things like deadly embrace lockups
which can cause everything to stop or rare conditions in which apparent
causality and temporal coherence completely inverts and things which
"cannot happen" happen exposing all kinds of reasonable but not
quite bulletproof assumptions.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Using a frequency synthesizer replacement for motherboard oscillator

[David I. Emery]

On Fri, Nov 30, 2012 at 04:24:38PM -0600, shali...@gmail.com wrote:
> I am not sure that a precision clock will help if the cpu is busy and skips 
> clock cycles. I believe this is one of the problems with general purpose OSes 
> like Windows.
> 
> I believe the better boards like the Soekis use hardware dividers to 
> alleviate the cpu busy problem.
> 
> Didier

For what it is worth, for many generations now all major CPUs
have had kernel software readable nanosecond level time of day time
stamping counters that are clocked from the incoming clock to the CPU
chip and run continuously and steadily without skipped or added ticks
whatever the CPU is doing.   And in addition to these time stamping
counters, most all CPU chip sets also include "real time clock"
interrupts which again are  driven off of continuously counting counters
referenced to the clock input to the CPU and can be programmed to
interrupt ever n ticks of the master clock - regardless of CPU activity.

Obviously while servicing the real time clock interrupts is
usually a very high priority, depending on how the OS works and what
privileges real time priority apps have occasionally a real time
interrupt can be serviced so slowly that another one happens before it
is cleared.   Some OS real time clock handlers attempt to spot these
cases and adjust their idea of time to compensate.

Any OS based PLL driven by time stamping 1 PPS timing interrupts
WILL see some jitter in its time stamps due to bus and internal CPU
latencies and use of interrupt off intervals to protect against race
conditions. This noise is unavoidable and does depend on CPU load and
even  how fast the CPU clocks are set to run at any instant (modern CPUS
dynamically adjust clock rate in various areas of their logic to
conserve power and reduce heat).

So for a very fine control a hardware based 1PPS event time
stamper will provide greater accuracy and less jitter, especially if it
is driven by a high accuracy external clock source locked to some time
reference.

But of course it IS  useful to clock the CPU with an accurate
clock as that then means the internal CPU time stamp counter and real
time tick interrupt is ticking at a known rate - starting from some
epoch that can be eventually calibrated over time - and multiple 1 PPS
ticks - within a few ns or so of 1 PPS GPS or other similar time.

If the CPU clock is unstable and wanders around with time,
temperature, power and fan activity it then becomes necessary - as the
timing 1PPS PLLs built into many modern kernels do - to try to measure
its frequency error and drift and estimate the error phase between it
and true time. If the CPU clock  is locked to a reference, this is not
as hard a thing to do as the only relative unknown is when exactly the
zero epoch on the counter occurred.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] 5061A AC Power connector

[David I. Emery]

On Sat, Nov 24, 2012 at 08:35:44PM -0600, J. L. Trantham wrote:
> Pete,
> 
> In the US, Galco sells a DDK product that works well.  The connector and
> shell are a DMS3106A18-22S.
> 
> http://www.galco.com/buy/DDK/DMS3106A18-22S
> 
> You will also need a clamp and strain relief.  I use a DMS3057-10A.
> 
> http://www.galco.com/buy/DDK/DMS3057-10A

Thanks, one less living in sin thing in my life...

An official connector !



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  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] WWVB New Modulation five cent demodulator / carrier regenerator ? (Dale J. Robertson)

[David I. Emery]

On Mon, Oct 22, 2012 at 02:16:19AM -0400, johncr...@aol.com wrote:
> Dale -
> 
> To your question re BPSK and DPSK. In both modes the phase shift is 180 
> degrees.
> Straight PSK has the issue of determining the 1's from the 0's, at the 
> receiver as there is
> no phase reference.
> To avoid this DPSK encodes the the serial data stream prior to the 
> bi-phase modulator.
> As I recall (at 1 AM) the method is like this. If the present bit to be 
> sent is a 1 the phase
> of the carrier is inverted. If it is a zero the phase is not inverted. 
> This is easily sorted out
> in the receiver using a flip flop and an XOR.

I might add one note.  Non differential PSK has a slight BER
advantage with very weak signals as differential PSK decoding causes TWO
bits to be in error in the recovered data if the phase state of a bit is
incorrectly determined by the receiver and the next and previous bits
were correctly determined.

For this reason most satellite nPSK modulations use absolute
encoding and determine phase in initial lockon by looking for a phase
which causes the inner FEC to work (eg produce valid corrected data).

There have been demodulators for differential nPSK that work
by correlating the last bit with the current bit using some kind of
delay line.   Don't typically work as well with weak signals though.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] HP Z3805A com port and monitoring questions

[David I. Emery]

On Thu, Oct 18, 2012 at 12:47:30AM -0500, Edgardo Molina wrote:
> Dear David,
> 

> Yes, I bought the same unit as you. I will come back to you tomorrow
> with some serial number information. 

I found mine is a DTE with TXD on pin 2... RXD on pin 3.

Seems to like 9600,8,n,1

Have it working under a XP virtual machine on this laptop with
the K8CU GPS receiver control program.   Seems to work OK...
no stats on performance yet.

Mine has a Motorola 6 channel GPS rx in it - not a Furuno 16
channel.   

In the same shipment  I also ordered one of the Samsung branded
Symmetricom GPSes that does have the Furuno 16 channel receiver.
K8CU GPSCON reports it has a GT-80 and shows 16 channels.  It has
a Symmetricom OCXO, looks MTIish... but not MTI.  Mounted on a
doubler board - outputs 10 MHz.   Looking inside the receiver
is a Furuno GT8031F.

I'm sort of wondering if I could upgrade the GPS in my close to
NOS HP z3805 box (would obviously require using the Samsung version of
the firmware) from the Samsung box... not clear how much (other than
TRIAM and WAAS) that might buy me or whether it would be worth it.

Though I am sure you know all this, you certainly should be able
to find the port pins with a DVM or scope - mine outputs about -8 volts
on TXD and RXD floats about 0.2 volts positive.   I did find I need a
null modem cable to connect it up to a regular serial port (for this
test a keyspan HS-19 USB serial port).

I'm not exactly sure what Said Jackson has and sings the praises
of.  Fluke.l has been selling a few Samsungs and has one advertised that
I guess is similar to mine but with an explicit MTI 260.

I presume Said has units with the 10811-60165 rather than the
MTI-260... I'm curious which oscillator  he is finding those stability
and phase noise specs on - I'm looking to upgrade the reference to some 
microwave LO chains and would like a nice box with that performance.

I'm not sure when he bought his or what age they are. 
Apparently some of the  HP branked z3805s must have had the Furuno
receiver module.

There is also tommy_chou who has some Samsung z8505As with
the 10811 DOCXO... not sure what GPS these have.

Appear to be 3 sellers with similar ex-Korea CDMA stuff...
tommy_chou,  our familiar fluke.1 and yixunhk.



> you are able to connect to your unit, please advise. None of the
> combinations I got in past emails worked. It must be cable or serial
> port, or blame it on the operator. I will update this thread with more
> information tomorrow. 

I have found the obvious pilot error issues with things like
hyperterminal - the box should respond to a *CLS command with scpi > and
to an *IDN? command with the serial number.   I did find (silly me) that
hyperterminal  defaults to DCD flow control on and you have to say no
flow control before it will see anything from the ports on the box. This
is because DCD comes out off with the Null modem cable I was using.

Basic stuff.


> I will be getting new toys to play around during the weekend. I will
> comment in a separate thread as soon as they are delivered to me. I wish
> to correspond with someone having the same equipment nowadays ; )


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] HP Z3805A com port and monitoring questions

[David I. Emery]

On Sun, Oct 14, 2012 at 03:15:53PM -0700, Said Jackson wrote:
> 

> I believe Edgardo bought the reprogrammed 58503A unit (was a Z3805A
> before) from Ebay.
> 

> I have the same units recently purchased from yinxhu(sp?) on Ebay and
> Edgardo just confirmed these are indeed 16 channel units with true 10811
> Docxos.

I just bought one from yinuxhk based on your comments last
weekend and it arrived today.

Has one RS-232 port and two 10 MHz and two PPS.  XLR 24 volt
power connector. Made in Korea, marked HP Z3805A std.

In very good shape. Seems like almost new old stock.  HP DOCXO.

Seems rather old based on serial number, serial is 3625Ax
which would be 1996 if IIRC.

I'm pretty sure what Edgardo bought exactly.

Are yours this exact version and what age are they (from the
serial number) ?



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Antique 5061A option 004

[David I. Emery]

On Mon, Oct 15, 2012 at 09:28:59PM -0400, David I. Emery wrote:

>   I live right near the business center of Weston on Boston Post
> Road... (west of the center).   If you know the area you might have
> noticed a house with some discreet satellite dishes in the back yard...
> and antennas on the roof...

Sorry world, this was presumed to be directed at Paul,
not the list...

I should always check, I know, but sometimes get bit...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Antique 5061A option 004

[David I. Emery]

On Mon, Oct 15, 2012 at 06:15:15PM -0400, paul swed wrote:
> David
> Yes indeed I picked mine up for $125. Many hours of fun though the tube
> really was bad. But sure learned a lot and as mentioned here on time nuts
> actually have it working with a 5060 tube. John mentioned your location and
> we are actually reasonably close. Like you I was at nearfest.
> So before you fire it up perhaps we should talk. Part of the weight may be
> the nicad pack and who knows what condition its in... Hope it did not vent.

I am about to look at the batteries.   I think they likely are
still there from the weight.   Those old nicads are less of a problem
than some new ones... I've got some old spook gear with those things in
it and while some were shorted none leaked badly.

As you may have learned John Forster ran into me as I was
carting the thing off... he offered to help move it on his motorized
wheel chair but I thought it too heavy and clumsy to try that - I'm not
very coordinated and of course since he had his diabetes problem he is
not agile either - might have made for a dicey situation.  In the end a
good Samaritan helped with one handle before I got to the parking area
outside the fence...

I live right near the business center of Weston on Boston Post
Road... (west of the center).   If you know the area you might have
noticed a house with some discreet satellite dishes in the back yard...
and antennas on the roof...

I'd be glad for advice before powering up, though I am eager to
see if it pumps down and beam I is reasonable.   It does seem to have
some mods for setting the C field - a stereo 8MM phone jack on the front
panel with a little label marked "M" and of course the C field output on
the back panel.  Neither appears original.

I did follow your adventures with yours, and of course on
another topic have been injecting my 0.02 into the discussions about
WWVB phase modulation on and off as well.

The current spec for that seems pretty rational to me at the
moment in fact... though I agree that with low signal levels and QRM and
QRN you will never be able to lock the signal reliably without some kind
of very low bandwidth PLL (eg a Costas loop).

It appears that one can predict many of the bits (and thus
phases), but not all of them - especially if they add various random
messages interspersed with the BPSK time info and given that one could
produce a de-PSK'd signal with a balanced mixer with some dropouts for
the early part of  unknown-in-advance bits.   Whether this would work OK
with antique receivers or not I don't know.   Would seem just as easy to
do a Costas loop and simply feed the antiques the carrier recovered in
the Costas loop though of course that does introduce another source of
phase error and phase drift.

The one liability of a Costas loop approach is long fades. You
would need either to provide a squelch of some kind that would stop
phase tracking or lock it to some kind of local reference based on the
local standard during fades.   The latter is quite possible, if you have
an accurate standard you are comparing with - all you need is to use
some digital processing (on a processor these days of course) to
synthesize a carrier in phase with WWVB and when the signal fades  feed
that to the loop until the signal returns.

If real time time of day operation is not required, another
technique suggests itself... simply delaying the signal by one symbol
time (in this case 1 second) by digitally sampling it with an A/D at
some convenient rate (like 1 MHz) and stuffing the samples into a
circular buffer before outputting them via a D/A.   During that bit time
it should be possible to correlate with a local digital generated 60 KHz
and determine the best estimate of the bit phase state.   And when one
gets to the best estimate of the 1 second splice, one simply adjusts the
phase of the sample play out by multiplying the samples by 1 or -1
depending on which phase state seems to correlate best with the signal.

A slightly more sophisticated version of that would use the
known time code most of the time and just use the correlation when the
bit state was ambiguous due to the possibility of messages.   That would
ensure that the 60 KHz phase in the reconstructed signal matched the 0
degree phase of the transmitted signal.

The 1 symbol time  delay technique ought to be able to handle a
very very very long fade given a decently accurate digital time base
since it is not necessary that the local synthesized (numerically inside
the software I would expect) 60 KHz have any particular exact phase
relationship to the WWVB carrier... clearly one would want to correlate
in I and Q space (eg with the carrier and the carrier shifted 90
degrees) and make ones best guess where on the unit circle the 0 phase
carrier lies...

When one returned from a fade one would want to try to
re-estimate the phase relative to the l

[time-nuts] Antique 5061A option 004

[David I. Emery]

In a mad moment at the NEARFest flea this weekend I grabbed
a 5061A for $250.   Poor thing was getting wet in the rain and needed
a home.  Really really heavy to carry to the car, however...

It has a high performance option 004 CBT in it (late SN
3112A02887 dated 05/93).   And a 10811-60109 OCXO.   Option 3 whatever
that is, and H29 too.   Seems to have a BNC marked C field...

Chassis SN is 2002A01710 but a number of the modules have  late
series numbers such as 2740 for the synth, 2652 for the oven controller,
and 2448 for the AC amp..

The unit obviously came from the Naval Observatory (similar
to Paul Swed's I presume)... has a sticker on it.

Looks superficially as if it was upgraded various times -
wondering if anyone could suggest where a manual that would cover the
OCXO mod and others on into the 90s might be had (Artek ?) 

I have yet to fire it up (gotta dig out a power cord I have
somewhere in the way back junque)... but FWIW (not much I am sure) I was
told it would lock "after a while".

I suppose it is time to see if it will pump down and have any
measurable beam current - I guess at least possible that a CBT that
young might still have a tiny bit of life left.

A question - I assume the OCXO is 10 MHz (I think all 10811s
are) and thus it obviously must be easily possible to provide a 10 MHz
output. Is there a point to attach a SMA to BNC for this ?

It is my first Cesium, now I guess I officially have the
disease, all those Rbs and GPSDOs being just prodromal syndromes...

I also grabbed a PRS10 at the flea (that was pretty cheap
at $50) and wonder where I might land a PBBT adapter for it cheap
too... I'd rather see if it works OK before investing in a new one
first... and that connector is a bear.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] WWVB Response

[David I. Emery]

On Thu, Sep 27, 2012 at 11:16:45AM -0700, J. Forster wrote:
> The bandwidth is secondary. The time-domain response of the filter is the
> issue.

Seems clear that you need a reasonably wide preselection filter
to avoid this problem, maybe as someone suggests several hundred or more
hz to really kill serious phase trajectory problems.

BUT this does not imply anything but that the dynamic range and
noise properties of the signal processing that deals with that bandwidth
must be able to handle all the energy there.   And yes, with a wider
bandwidth there WILL be more noise and crud at the output of the RF
preselection.   But not so much as to make a quadrature multipliers
(mixers) for a Costas loop unimplementable.

The actual tracking or detection bandwidth can - however- be
made arbitrarily small using a standard - known for 70 years - Costas
loop - and is a function of the LPF characteristics in the Q arm...
and of course the drift and random noise (eg Adev) characteristics
of the VCO (and signal and propagation).

Since both the local loop VCO and the WWVB carrier are assumed
to be from reasonably high quality stable sources and propagation is not
expected to be wildly variable this bandwidth in locked mode can be made
almost arbitrarily small... hundredths of a  Hz or less...

And THAT bandwidth is the true noise bandwidth.

The only real issue in such an approach is locking the loop in
the first place... it will be necessary to start with the VCO close to
the carrier or widen the loop bandwidth initially in search mode.   In
the digital or data domain of course FFTs help here a lot.


> 
> -John
> 
> =


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Datum PRR-10 Info

[David I. Emery]

On Sat, Aug 25, 2012 at 11:41:21AM -0700, J. Forster wrote:
> Hi,
> 
> I recently picked up the Rb module from a Datum PRR-10 Precision Reference
> Receiver.
> 
> The Rb connections are pretty obvious, but does anybody have any info on
> the rest of the module? Even a schematic would help.
> 
> I'm trying to decide whether the PCB has anything useful on it.

I have the whole working PRR-10 system including 2 Rbs and AFAIK
that PCB just contains redundant power and provisions for passing a
couple of status bits from the RB (lock I think)... if you have a PRR-10
system it would be useful, but I'm not sure it is otherwise.

Possible there is a -48 volt input DC to DC converter... if it
would be useful I go go look at one of mine to refresh my memory.

The heat sink is useful with the LPRO RB of course.

I assume you bought it for the LPRO...

You may not be aware, but the system is designed to use a DDS to
offset the frequency of a free running 10 MHz source to make it accurate
based on GPS timing ... so the Rb is not disciplined with its C field or
similar - it is free running.




> 
> Thanks,
> 
> -John
> 
> 
> 
> 
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-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Lightsquared questionfor SFO area....

[David I. Emery]

On Fri, Jul 27, 2012 at 09:42:49PM -0400, Brian, WA1ZMS wrote:
> Does anyone know if there is ANY recent active Lightsquared testing taking
> place in the SFO area of the US?
> 
>  
> 
> I'm dealing with a day-job issue with GPS clocks in the Bay Area showing
> "GPS unlocked" errors from 3rd party equipment.

Do you have a good SA available and some broadband antennas...

And perhaps some logging program like John Mile's SSM ?



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] HP 3586B Selective Level Meter

[David I. Emery]

On Fri, Jul 20, 2012 at 02:51:33PM -0500, Peter Gottlieb wrote:
>Hmmm!
> Subpart H--Rules Applicable to All Broadcast StationsSec. 73.1545  Carrier 
> frequ
> ency departure tolerances.(a) AM stations. The departure of the carrier 
> frequenc
> y formonophonic transmissions or center frequency for 
> stereophonictransmissions
> may not exceed  20 Hz from the assignedfrequency.
> 

Bet they have an oven problem

Some modern SAs will do this stuff too... when fed a good
10 MHz reference.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Phase modulation detection/NIST plan

[David I. Emery]

On Sat, Jul 14, 2012 at 06:15:14AM -0700, J. Forster wrote:
> I don't see why school crossing signs, water sprinklers, street or outdoor
> lighting need 1 second timing. Ten minutes, or a photocell, would be more
> than adequate.

While there are many many other applications, the issue for most
of these devices is not 1 second accuracy, but automagic setting of the
time without operator intervention or manual procedure required. For
many ordinary folks the always slightly different push button gyrations
required to set the time on a device with limited buttons and display
are all too often a complete barrier to getting the time set right (this
is the VCR "blinking 12:00AM" phenomenon).   And in outside environments
clock oscillator thermal behavior will ensure something preset to the
correct will wander pretty far out quite quickly  (plus of course DST
needs to be set too).   And working with only approximate time is 
another source of terrible confusion for users... if they set it to go
off at exactly 11 PM and it goes off at 11:08 PM they are likely going
to be confused and frustrated... especially if difficult or even
impossible steps are required to correct the time.

Photocells don't work for situations where the desired on or off
times are civil times (not turning on the water sprinklers until 11 PM
for example or turning off the tennis court lights at 10 PM)... at best
it takes lots of software to convert light and dark from them to
anything approximating a 10 minute accurate estimate of the time of day
and shadows and sun angles and so forth ensure that this is never going
to be particularly accurate.


> Synchronized traffic lights, perhaps. But there are other cheaper, ways of
> doing that like a simple radio link.

I refuse to believe that a reliable mile or more range RF
link would be cheaper than a loopstick and maybe a couple of passives
tied to pins on a SOC chip...  and there are all those situations
where even a mile isn't enough or obstacles or RFI block ISM band
links.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Phase modulation detection/NIST plan

[David I. Emery]

On Fri, Jul 13, 2012 at 09:47:12PM -0700, Brooke Clarke wrote:
> Hi:
> 
> The key thing GPS is lacking is Daylight Savings Time.
> 
> WWV & WWVB have the DST bits that allow a clock to show the local time.

And that is important for most routine civil human use.

Nor something that could somehow be added to GPS which is
worldwide in scope without adding lots of message information and
dealing with all the crazyness of international time zones and
political jurisdictions.   WWVB serves the US (and maybe Canada) 
where DST start and end is pretty much global.

Besides the costs greatly favor WWVB receivers... as the
authors of the paper point out their whole decoder would fit neatly
in a tiny corner of the silicon of a typical SOC chip these days...
and AFAIK there is no practical current way to do this with GPS.

And while it is true that good Faraday cages like metal
enclosures with tight seals kill the LF, a good sized bush might take
out GPS and won't impact LF reception, which also works pretty well
inside many buildings and in particular common wood frame houses unlike
GPS.



> 
> Have Fun,
> 
> Brooke Clarke
> http://www.PRC68.com
> http://www.end2partygovernment.com/2012Issues.html
> 
> 
> 
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-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Phase modulation detection/NIST plan

[David I. Emery]

On Sat, Jul 14, 2012 at 02:38:34AM +0200, Magnus Danielson wrote:

> I think the PTTI article isn't as much documentation as presentation of 
> general principle, showing details more as to present how it can be 
> done, but not necessarily guarantee it will be done that way. Knowing 
> the synchronisation sequence, polarity should not be ambiguous. Also 
> note that other data such as hours would be known from the AM signal, so 
> we can reverse engineer it. A receiver knowing this sequence will either 
> bootstrap from the AM or attempt straight lock. It's not too hard to 
> build a maximum likelihood receiver for it.

I read the article as not a definitive specification frozen in
stone, but as a complete and relatively fully specified proposed design
with perhaps some details subject to adjustment or revision.

The question of absolute versus differential phase shift keying
is, of course, rather fundamental to being able to decode the signal at
one level but at another not terribly central to the core of the design
for a coding and modulation scheme that works at much lower C/N levels
than the AM version did while preserving the legacy AM and its coding
for existing hardware.

SOME place in the design of a differentially coded signal there
has to be a decision whether or not to structure the data encoding  so
some specific bit (or more properly symbol) in each frame (or at least
some known frames relative to the time of day) (in this case I mean 1
minute long TOD frame) is of a known absolute reference phase.

If this is done than it becomes possible in a reasonable time to
determine an absolute  60 KHz carrier phase after a fade, if it is not
done and every single bit of data is not absolutely predictable (the
current TOD coding would be absolutely predictable given knowledge of
the time and date and  of leap seconds and DST settings, but they make
clear future extensions would probably not have this property as
additional messages are added including emergency messages and the like
which are never predictable) there is no way to reliably decide after a
fade which phase is which as this depends on knowing the number of ones
and zeros in all the frames transmitted since one last saw the signal,
something that is in the general case impossible if the signal has faded
and the bits were not observed.

An absolute encoding has no ambiguity - if one knows the time of
day within a second one knows the transmitted phase except for during
bits that might vary with unknown data (eg emergency messages,
extensions to the standard and newly changed DST and leap second
settings and FEC bits based on them) and MOST bits are always known
phases, especially of course the sync code words.   So even with
terribly poor C/N one should be able to relatively quickly resolve the
phase ambiguity after a period of signal loss... and in many cases if
one still has a good idea of the time, within a couple of seconds
(symbols) of signal reacquisition.

On another point, I am not of the school that providing much
better weak signal performance for simple, low power, and cheap LF time
of day clocks using  WWVB is somehow a minor improvement that primarily
benefits China because they make most cheap self setting "atomic"
clocks.   There are innumerable applications for low cost low power
human level 1 second accurate time of day in modern electronic systems -
examples are traffic lights and school crossing signs and water
sprinklers and street lights and other outdoor lighting and many
others... these systems are not normally network connected  and there is
no current wide area technology short of power hungry GPS with its weak
signals and relatively high cost and difficult reception from many
locations to do this.

And with minimal effort to ensure compatibility, there should be
no conflict with use of the same carrier signal as a frequency reference
too... the problem of several decades old antique time and frequency
gear being incompatible seems very minor, and of course we have already
discussed ways to handle this if needed.

And as long as the existing frequency reference use of the
carrier continues to work as a backup to GPS with modern updated gear
that capability hasn't been lost - except maybe if your particular
variety of tin foil hat requires vacuum tube VLF reference gear because
of EMP fears or something similar.

I think the new WWVB proposal seems sensible and a reasonable
design...that should serve the public well.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Phase modulation detection/NIST plan

[David I. Emery]

On Wed, Jul 11, 2012 at 03:48:52PM -0400, paul swed wrote:
>  David
> Read your comments and have been traveling. So finally a chance to email.
> 
> I read the document also and walked away with what I shared.
> In your reading would you believe the following.
> Its an absolute phase and that when it switches to 0 there is 1 transition
> at the beginning of the second to 180 degrees staying that way to the next
> bit or flipping again to 0 degrees if its a 1 at the 1 sec tic???

What I mean by absolute phase is that a 1 is always 180 degrees
and a zero always 0 degrees.  In your example this would imply that the
two ones in a row would result in two seconds of 180 degree phase
without a flip after the first 1.

The document is confusing, but the best I can do with its
language is to conclude they are talking about absolute phase.  Normally
when one talks about baseband waveforms one is referring to absolute I
and Q components relative to an unchanging carrier phase, not relative I
and Q with respect to the last bit phase.   So I take their language to
mean a zero is 0 degrees and a 1 180 degrees relative to an unchanging
carrier.

Differential encoding is the opposite, a 1 is always the
opposite phase from the last bit, a zero always the same phase as the
last bit (or sometimes  the inverse where a zero is the transition and a
one is not).


> Is there a way to sense from the document that there is a bias towards 0
> lets say.

Differential encoding tends to have little "DC" component or
bias toward either one or zero or one phase or the other, absolute
encoding does if the data it encodes does.

--
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Phase modulation detection/NIST plan

[David I. Emery]

On Sun, Jul 08, 2012 at 09:02:53PM -0400, Bob Camp wrote:
> Hi
> 

> The gotcha is that they may change the sync word based on test data.
> They may also tweak other vague points in the spec based on the troubles
> they run into in their tests or with their silicon. 

I finally read the wwvb.pdf paper (yes, do so before opening
mouth)...

I think I read the "Binary Phase Shift Keying Modulation"
paragraph on page 10 to indicate they are using ABSOLUTE, not
differential BPSK.

They refer to the "baseband waveforms s0(t) and s1(t)".   To me
this is the absolute I vector... and this clearly says  that a 0 is
always upward (or by convention in phase), and a one is always downward
(180 out)...   They clearly say the phase shift is 180 degrees... 

I would think this clearly could be phrased better...

It appears the data format they propose is quite well defined in
the paper, though they clearly indicate that a proposed extension is
changing the barker code sync word for frames every so often so as to
indicate a different frame type that might contain highly entropic (eg
volatile and unpredictable) information of  undefined character
including a possible mechanism for sending arbitrary and completely
apriori unpredictable bitstreams, though doubtless constrained by the
hamming codes used for FEC/error detection and the barker code sync
word.

On a quick read it appears the complete 60 second time frame
format is defined unambiguously.   There are somewhat unpredictable DST
bits and leap second bits in there... but in practice those change VERY
infrequently from 60 second frame to frame or even from week to week
or year to year. (Yes Congress likes to muck with DST every decade or
so...).

I am still reading more carefully, but I think this means that
the entire phase and amplitude sequence of the signal is defined for the
current initial version if you know the time of day and date and the
current leap second and DST settings (which change VERY infrequently).  
And I *THINK* I understand this means the absolute phase sequence
relative to the 60 KHz going into the modulator at the transmitter 

Thus the initial signal phase modulation could be removed by
some comparatively simple itty bitty microp software driving a balanced
modulator  BUT future signal extensions might not have that property.

As for acquiring bit sync with the signal, both the amplitude
and phase information should allow a micro to do this easily and
relatively quickly if the I vector were provided to the micro somehow.
This would presumably be possible by either sampling the 60 KHz directly
with an A/D (at 240 Ksample/sec) or by using an external balanced mixer
driven by local synthesized 60 KHz.   Even just an envelope detector
would work with strong signals because of the AM  component, and this
might be enough to acquire adequate bit sync for some purposes.

Software PLLs at 1 second rate are duck soup for even a SLOW
micro... and frequency errors are tiny so tracking can be tight. And
acquisition for these is also very fast given reasonable SNR. Only takes
forever if SNR is so low it takes that many seconds correlation to see a
reliable tick.

I admit as I think about this that if one synthesized the clock
for a itty bitty simple micro from say a local DUT 10 MHz whose phase
relative to WWVB one is monitoring one could do much of the entire job
by using programmable timers on the micro and its internal A/D.   This
includes phase error versus WWVB output and of course TOD output.

One would almost certainly want to either use external balanced
mixers (FET switches ?) and produce an analog I and Q (low pass
filtered) for processing by a really slow micro or use a fast enough one
to take a stream of actual real 60 KHz input samples at 240 KHz and
compute filtered I and Q)  (and LP filter/decimate it) (yes, with
accurate A/D clocking from suitable microp output pin interval timers
you might well be able to subsample by a lot and not actually ever deal
with even any close to a  240 KHz sample stream with the micro).

This would of course allow computation of the vector positions
of the WWVB signal modulation in I and Q space relative to the 10 MHz
clock from the DUT.   And from that one should be able to compute
the various moments of 10 MHz DUT clock drift and do a decent job
of compensating for it (better and better as the DUT clock gets more
stable/predictable) and ride out fairly long fades and outages without
losing a pretty  good idea of the expected WWVB phase.   

Presumably most standards whose phase one is tracking with such
setups are very stable, thus the holdover should be considerable
if one uses a good error and drift estimate to adjust ones local
idea of WWVB phase relative to local clock derived from the standard
to compensate.   And guess what, determining a local error and drift
estimate is precisely what such 

Re: [time-nuts] HP 117/10509a...

[David I. Emery]

On Thu, Jul 05, 2012 at 04:19:25PM -0700, J. Forster wrote:
> If propagation goes south, you loose track of the carrier phase, the basis
> of the system. If your local standard is stable and close to right, that's
> not a big deal. If not, you can easily go down the garden path.

If I read this correctly, you mean you have a 180 degree
ambiguity due to the BPSK - obviously losing track of the carrier phase
in general with a significantly wrong local standard loses...

I have not devoted enough time to this to be absolutely sure but
it sure sounds like from what I read that if you know the accurate time
to one second it should be possible to unambiguously predict the carrier
phase sequences simply because you know the message format exactly, AND
you know the exact time of day message that is being transmitted or most
of it.

There are of course two forms of encoding in PSK modulations -
absolute, and differential (or transition) ... naively to me it would
seem that if absolute encoding is used for this and you know most of the
bits of the message most of the time you could predict which phase will
be used a lot of the time, and also know when you don't know (message
bits you might be uncertain about)... 

Differential encoding has the down side for this that UNLESS you
know all previous message bits accurately starting from some phase
reference datum you cannot predict what phase is in use at a particular
moment.   Absolute encoding (eg 0 phase for a 0, 180 for a one) doesn't
have that liability and if the time of day message is aligned to, well,
the time of day if you know that with reasonable accuracy (and you do
since you are being sent it in the first place) you should be able to
predict a very large percentage of phases used accurately.

Again, deferring to those who have done the experiments (which I
have clearly not), it would seem that the ability to predict the phase
most of the time would allow creation of a reliable local 60 KHz
reference which could be used to disambiguate those bits you don't know
apriori

My naive scheme would be to drive a balanced modulator on the
output of the 60 KHz loop antenna with either two or maybe three values
(1 and -1 or 1,  0  and -1) using some cheapie micro (Arduino, PIC etc)
with a software PLL to keep the bit timing in sync with the signal.

For bits that one could not predict, one could either output 0
to the balanced modulator for the entire bit interval  which would
produce a drop in the 60 KHz carrier, or do a fast timed fraction of a
bit look at the output of a synchronous detector and choose the most
likely value for the bit and use that, maybe after a brief 0 no carrier
interval to avoid a detectable phase glitch.

Of course the other approach is to start with the assumption you
have a pretty good stable source of clock or you would not be doing this
to begin with, and simply A/D the 60 KHz with the stable clock (say at
10 MHz), delay it by storing samples in RAM for one bit time of the low
speed code  and use that entire interval to decide which phase you were
seeing and suitably adjust the output phase accordingly when you spit
out the samples delayed by one bit time.

This later approach would certainly be doable with modern
processors mostly in software, certainly so if you could live with say 1-2
MHz sampling of the 60 KHz or so... and quite possibly also pretty
nicely with a modest FPGA complete with the sample storage in the chip. 

Both approaches would be helped a lot if the architecture of the
system allows prediction of absolute phase (eg not differential encoding
of unpredictable messages)... and AFAIK that is not yet set in stone and
could be changed to allow this.

The intent of both of these schemes would be to ultimately 
output a De-psk'd signal that older equipment could process using its
antique analog circuitry without serious issues.   Thus the output
would be an attempt at a phase stable corrected version of the original
signal...

Certainly using a lab reference stable 10 MHz derived 960 Khz 
or whatever sampling clock to delay the signal one time code bit time
should not produce significant 60 KHz phase wanderings at all...

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] ANN: UK MSF 60 kHz interruption, 2012 June 14

[David I. Emery]

On Sun, Jun 03, 2012 at 09:20:59AM -0700, J. Forster wrote:
> Is there any indication the carriers of WWVB and MSF are locked together?
> 
> -John
> 
> =

Given it's only 60 KHz and certainly somewhere north of parts in
10^13 and probably  down to 10^14 or 10^15 the distinction kinda escapes
one.

They may not be locked to each other, but are so close in
frequency that relative drift would be AWFULLY slow... especially if its
more like 10^15 from primary maser standards...

There are only 5.184 * 10^9 cycles of 60 KHz  in a day after
all... and it takes a while for a error of a few parts in 10^15 to
pile up to one whole cycle...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] frequency (absolute) accuracy in sound recording/playback

[David I. Emery]

On Mon, May 07, 2012 at 06:13:56PM -0700, J. Forster wrote:
> A movie may be 7000 seconds, and you may need a fairly stable timebase,
> but every movie I've watched is made up of short (<300 second) scenes that
> are placed sequentially on the framework.

5-10 seconds a cut is quite common, and less than that usual
for some things.

Digital video has a timing mechanism (PCR) built in that
is intended to take care of this... everything is time stamped in ticks
of a 27 MHz clock... and all the renderers locked to that time base.



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Oh dear

[David I. Emery]

On Mon, May 07, 2012 at 08:28:41AM -0700, J. Forster wrote:
> A crummy crystal oscillator zero beated to WWV is good to 1 in 10E6, a Rb
> disciplined to GPS maybe 1 in 10E11.
> 
> Do you seriously think you, or anybody, can hear a pitch difference of
> 0.001 Hz in the audio range?
> 
> A quartz crystal is plenty good for any audio application, IMO.
> 
> -John


I completely agree, and far more significant than accuracy
is jitter (phase noise) in maybe the tenths of a Hz to thousands  of Hz
area.   This does modulate the sampled sound and perhaps is perceptable
at very low levels.

BUT Cesium, or Rb buys nothing in respect to phase noise
in those ranges... really good quality quartz oscillators have much better
close in phase noise than many Rb's or Cesiums...

What Cesium and Rb buy is good performance measured over much
larger taus... which cannot possibly have any impact on human hearing.



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] LORAN-C at MIT

[David I. Emery]

On Sun, Apr 15, 2012 at 05:54:31PM -0400, paul swed wrote:
> Yet another time nut that makes at least 4 at MIT! Thats a very dense
> population.

I sometimes go myself, making at least 5... wasn't there this morning
though...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] WWVB BPSK Receiver Project?

[David I. Emery]

On Wed, Mar 14, 2012 at 05:13:47PM -0700, J. Forster wrote:
> Now it looks like they are going to kill WWVB, which is a bit more
> involved, but works.
> 
> GPS is not an option without a tall tower.

Everything you say up to this makes perfect sense, but what makes
you think GPS timing fails to work with less than a tall tower ?

I believe it is readily possible to get to the 10-30 ns of
UTC/TAI TOD area with just reasonable sky view, not 100% as implied by a
tower. And certainly 1E-11 or 1E-12 frequency accuracy is also readily
available with less than perfect sky view depending on your taus...

Perhaps ultimate performance requires really unobstructed sky view
in order to absolutely minimize multipath but then you are probably 
talking 1E-13 or better... 


> This is NOT progress, IMO.

Virtually ANY GPS timing solution ought to easily get you inside of
a couple of microseconds of UTC/TAI, I am pretty sure it is quite difficult
to get within 10-100 us with the current AM modulation of WWVB, possibly
even 1-10  ms is difficult.   And anything close to this requires accurate
knowledge of geographic position and 60 KHz propagation corrections.

I'm not clear how accurately one can resolve the phase transition
in the new scheme, but I suspect probably unambiguously to 1 cycle of
the 60 KHz... and from there is merely a function of how accurately one
can resolve the phase of the 60 KHz.This potentially can supply a
much higher resolution time hack than the AM envelope.

The real question being how important is preserving backward
compatibility with antique equipment versus better performance...

I agree that ALWAYS is a trade off...


> 
> -John
> 
> ==
> 
> 
> > Hi John:
> >
> > They are going to maintain the existing AM modulation format so all the
> > WWVB "Atomic Clocks" will still work.  The phase
> > modulation is added on top of that.
> >
> > Yes, I expect my HP 117 may no longer work, but I'd much rather have the
> > improved s/n and timing accuracy.
> >
> > Have Fun,
> >
> > Brooke Clarke
> > http://www.PRC68.com
> > http://www.end2partygovernment.com/Brooke4Congress.html
> >
> >
> > J. Forster wrote:
> >> All very nice, but if this change renders all existing receivers
> >> useless.
> >> How does that improve things?
> >>
> >> All it does is wipe out all the existing phase tracking infrastructure.
> >>
> >> The only benefit is to the government who can reuse the WWVB transmitter
> >> and frequency allocation. Everybody else will have to buy new stuff.
> >>
> >> Sounds a lot like HDTV fiasco. Making jobs (in China or Korea) by making
> >> scrap.
> >>
> >> YMMV,
> >>
> >> -John
> >>
> >> ==
> >>
> >>
> >>> Dear Time-Nuts,
> >>>
> >>>
>  I sure would like a WWVB BPSK receiver for the new modulation. (..)
> 
>  I'm sure in time there will be plenty of low cost ICs designed to
>  receive the
> >> [SNIP}
> >>
> >>
> >> ___
> >> time-nuts mailing list -- time-nuts@febo.com
> >> To unsubscribe, go to
> >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >> and follow the instructions there.
> >>
> >>
> >
> >
> 
> 
> 
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-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] US New Year countdown - accurate?

[David I. Emery]

On Mon, Jan 02, 2012 at 11:57:55AM -0500, w...@aol.com wrote:

> FYI...  NBC advances their video feed, so that it arrives out of  the
> station receiver on time.

Several nets do this - of course useless when real time events
are being televised... as the delays are still there, all this means
is the schedule time base (station breaks, commercial slots etc) is
on real time at some point in the chain, doesn't of course make the
ball drop on time out of the IRD... unless they drop it early.

> Another FYI...  NBC video delivered over Dish Network are  delayed
> 14 -15 seconds...  all that processing between the TV station
> Dish/DirecTV receive site and the consumer!!

Much of the delay here is due to absolutely maxing out the
quality per unit bandwidth of the oversubcribed lower than ideal bit
rate video... they way they get so much stuff on those transponders
is very very carefully optimized variable bit rate video, which of
course works best with really deep buffers to look ahead for scene
changes and motion and optimally up the bit rate for just those.



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] US New Year countdown - accurate?

[David I. Emery]

On Sun, Jan 01, 2012 at 09:14:03PM -0800, J. Forster wrote:
> I was referencing anything to an external, local reference. My comment was
> the time difference between the FOX on screen timing and the ball dropping
> fireworks. Presumably, the on-screen timing was inserted at their local
> control center in NYC, not after satellite hops.

Fox was producing and uplinking that in NYC, though I suspect
the primary link back to their master control was fiber through the NYC
media switch with very low delay.I was not watching the Fox show
(don't watch much Fox) but I rather suspect the production trailer was
where the screen overlay got added to the video.

Doubtless nobody bothered to get the time on the graphics
inserter system  set to match the real time and camera video... most of the
time nobody cares or notices.   Quite possibly it has manually set time
of day from a web page or front panel rather than even house time codes, which
themselves may not be GPS synced.



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] US New Year countdown - accurate?

[David I. Emery]

On Sun, Jan 01, 2012 at 05:54:46PM -0800, J. Forster wrote:
> To me the ball drop/fireworks was different from the on-screen time on FOX
> by a few secnds.

I was watching the media pool HD satellite feed on AMC-1 and
through a broadcast grade IRD (ex PBS Bitlink ) it appeared to be about
2 seconds slow relative to  my house NTP timing.   This would about
exactly match what I would expect for uplink encoder, satellite path,
and decoder delays.

I would expect a TV station using that feed might add anywhere
from 1-6 seconds to the delay in their internal processing to OTA... and
a digital cable system might add further delay to that (couple of more
seconds at least).

Real time TV these days is only RELATIVELY real time.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] GPSDO recommendation

[David I. Emery]

On Wed, Oct 12, 2011 at 07:33:29AM -0400, Peter Gottlieb wrote:
> I would like to get better than 100 uSec so I can get a couple of degrees 
> resolution on a synchrophasor project.

Once one gets into that region with OSes one gets into a kind of
relativity... 

It all depends on what you intend to do with the time of day... 
and where.

Do you intend to schedule events with some required absolute
time accuracy as to when they occur ?   Or time stamp an event with  a
time it occurred ?   Or read something that purports to be the current
absolute time of day in the midst of some code path. Or do one of several
other time related things...

All involve fairly deep questions about what assumptions you
make about both software and processor and system hardware behavior.

Modern processors with multiple pipelines and even multiple
cores and (especially multi level cache) memory systems have layers and
layers of not all that deterministic behavior which introduce
microsecond level jitter in the relationship of the time anything
happens and the time the system reacts to it...

And that is usually dwarfed by the various thread and process
scheduling and interrupt processing latencies in almost any OS - some
versions, properly configured, being much more hard real time than
others.

Most OSes can most readily schedule something on a particular
clock interrupt of a multi KHz rate real time clock interrupt stream -
usually (with normal hardware) based on a not very accurate or terribly
stable crystal.Whether that something actually happens close to the
time of that clock tick depends very much on thread priorities (usually
set by the user as well as the kernel)  and CPU load and interrupt
activity and how well tuned that particular kernel is with respect to
minimizing long lockouts due to critical regions in kernel code or
contention for locks and resources.  And on top of this there may be
contention and lockouts in the actual hardware... 

And most all CPUs have high rate time of day counters that can
be read by the OS - also typically based on a relatively poor frequency
reference - almost always the same one used for the RTC interrupts.  
This can be used to establish with high precision the counter time the
counter was read, but the relationship of this to an external event
depends on how the kernel detects the event and with what priority and
latency. And of course the counter time of day is always somewhat off
due to the drift of the frequency reference behind it.

NTP and various related kernel PPS code attempt to use an
accurate stream of 1 PPS (or whatever)  interrupts from a highly stable
and accurate external ticker somewhere to measure and predict the
behavior of the drifting unstable CPU clock so it is possible to compute
a running estimate of  offset between the time of day counter on the CPU
(and the real time clock interrupts) and some external idea (from the 1
PPS) of the real world time of day.   This allows conversion of a
reading from the time of day counter to some notion of real world
time... and in most OSes the kernel does this for you and returns a time
of day rather than time counter reading (or more properly does so if
asked).

And depending on the OS there may also be an ability to attempt
to determine the real world times at which the regular RTC interrupts
happen so an event can be scheduled as close to some absolute time of
day as possible.

However the magnitude of jitter can be significant, and
its statistics not always easy to predict... 

And most important if there are multiple sequences of events
occurring it may not be possible to predict or ensure that events that
have a particular time sequence in the outside world appear to have the
same  ordering in time to the software... or even the same sequence to
different threads... 

All of which means that using such tools to control or measure
60 Hz (I assume) phase within a degree or so depends very much on system
and software choices - certainly readily possible if done right but at
least on a very slow or heavily loaded or poorly configured platform
also quite possible to occasionally have significant transient error.

Most folks who have played with measuring kernel time base
performance with modern *nix kernels and PPS sync find low microsecond
timing jitter is pretty much the limit... though lots depends on
hardware and software implementation details.

One suspects if one needs anything down in that low us area or
below a FPGA based much more deterministic approach might make sense...
with software and OS only configuring, supervising  and monitoring.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration o

Re: [time-nuts] Am I the only Time Nut who doesn't wear a watch?

[David I. Emery]

On Sun, Jul 10, 2011 at 08:48:07AM +0530, Raj wrote:

> Analog generation *know* the time from the position of the
> clock hands. By the position of the hands you know how many minutes left
> to an appointment etc. IF you ask them the time then it will take a
> moment to convert it to words!

I had occasion to observe two generations of extremely
intelligent women in my family as they approached death and began to
seriously lose mental acuity weeks or months before the end - both of
them completely lost the ability to make any sense out of the time on a
digital clock well before they died but were perfectly comfortably able
to read and understand an analog clock with hands and numbers almost to
the end.

Apparently for those who grew up in the analog clock era and
only had analog clocks around when they were little the mental
processing involved in reading and understanding the time from an analog
clock face is deeper and different from the mental processes involved in
dealing with the time in digits... which was a later learned skill and
seems to take more or at least different parts of the brain.

So yes, one's fundamental mental model of the time may well be
deeply enmeshed in the angles of the hands on a clock, rather than the
abstractions of hours and minutes.

I think little children do (or did) learn 3 O'clock as a pattern
of hands on a clock face associated with a particular time of importance
(time to take a nap or whatever)  well before the abstractions of
numbers, or hours and the significance of 3 hours after the meridian
mean anything.How children in the digital age learn time is an
interesting question...


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] time-nuts Digest, Vol 84, Issue 25

[David I. Emery]

On Fri, Jul 08, 2011 at 08:12:42PM -0400, brent evers wrote:
> I've actually found the separate mechanical and digital displays quite
> useful.  I spent a lot of time on science vessels and would set one to
> "science time" (GMT) and the other to what ever timezone we happened
> to be adhering to for daily operations, which can vary quite a bit
> when you are working near the poles.

This watch does that, it has dual times of day and a mode where a 
secondary window displays the second time zone with the hands and the
primary display on the other.

Interestingly the two times it keeps can be off in the minutes and
hours, but not in the seconds.   Are those world cities where for religious
purposes mean solar time is observed only on even minute boundaries ?



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] time-nuts Digest, Vol 84, Issue 25

[David I. Emery]

On Fri, Jul 08, 2011 at 11:11:34AM -0700, Burt I. Weiner wrote:
> Being in broadcast I need to know what time it is. I wear a wrist 
> watch with real hands on it so I can tell what time it is.  For a 
> wrist watch, I personally don't care for a digital readout.  I grew 
> up with a wrist watch that had real hands and I learned to tell time 
> and how much time I had simply by looking at the position of the 
> hands, I didn't have to do any math at all in my head.   All that I 
> need to know, for example, is that I need to be somewhere in 3/4 of a 
> turn of the big hand.  In my case I don't always need precision time, 
> I deal with that separately.

I actually wear an 80s AE-20W Casio watch that has both
synthetic LCD hands on a clockface and a normal digital time display.  
The LCD hands are sync'd with the digital display - unlike some hybrids
where a mechanical type movement driven by a step pulse was combined
with a digital time/stopwatch/alarm display that had no other connection
to it other than a common timebase.



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Lightsquared goes Global...

[David I. Emery]

On Thu, Jun 30, 2011 at 03:29:49PM -0700, J. Forster wrote:
> If over-the-air TV were abolished, that would leave all broadcast media in
> the hands of Comcast and Verizon and their $100+ charges.

Broadcast TV will never go away... far too important to the
political class as a place for political ads and local news about the
local congresscritters.

But you forget satellite DTH TV Dish and DirecTV have tens
of millions of subs now... it's not just Verizon and Comcast.

> 
> It amounts to a communication tax on the entire population.

Pay cable content seems to be succeeding in the marketplace
despite its higher price to consumers... and the continuing presence of
"free" broadcast TV.

And more and more of the quality content is there and only there
(and on the Internet for pay too).


> 
> -John


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] HP 3586 entirely referenced to 10MHz: A solution II

[David I. Emery]

On Mon, Apr 04, 2011 at 07:19:38AM -0400, Chuck Harris wrote:
> Basically, the higher the division ratio in a PLL synthesizer,
> which is what you are describing, the greater the phase noise.

No question about that, indeed.

But I am talking about a very low bandwidth loop (presumably
well under 1 HZ should work) which means the phase noise contribution
from the dividers and reference should be only inside that 1 Hz
bandpass. Outside of that the original crystal oscillator phase noise
should control, and while this won't improve that it also won't make it
any worse.

>
> You can think of it this way: Both the reference, and the oscillator
> being controlled, need to be divided down to some common frequency
> that you feed to the phase detector.  The entire time the counter is
> counting up the cycles to get you a cycle of that common frequency,
> the oscillator is not being disciplined.   It is only after the
> count gets done that the phase detector can compare the two signals
> and create a correction correct for the error in the oscillator.

True, but I am pretty sure the original crystal oscillator (even
modified with a varactor for tuning) was not phase-noisier than the rest
of the instruments LOs.  It is, after all, a LF crystal oscillator
running at 13 or 17 KHz with presumably a high Q crystal which shouldn't
to the first order have unreasonable phase noise in the band around it. 
The original problem was that this oscillator was not locked to a
reference and could drift a few tenths of a HZ (and maybe even Hz)
randomly with temp - not that it had too much phase noise.


> 
> The DDS is essentially a hardware solution to finding a suitable
> divider ratio to convert one frequency into another.

I do understand DDSes.
> 
> -Chuck Harris


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] HP 3586 entirely referenced to 10MHz: A solution II

[David I. Emery]

On Mon, Apr 04, 2011 at 02:00:14AM -0400, David I. Emery wrote:
> On Sat, Apr 02, 2011 at 04:13:55PM -0400, Chuck Harris wrote:
> 
> > Unlike simply stabilizing the BFO crystal as you propose.
> 
>   Has anyone given any thought to an alternative - phase locking
> the original BFO Xtals with a very narrow bandwidth loop to something
> derived from the 10 Mhz standard in such a way that the final frequency
> of the BFO comes out exact ?   Looks to me (superficially without looking
> at the schematic carefully) like this might be possible too...

To elaborate a tiny bit, if you divide 10 MHz to 25 HZ you could
use that as the reference for a classic PLL loop that stabilized the
crystals with a varactor... provided of course suitable low pass
filtering was used.   There are also approaches involving doing early
late sampling of the BFOs on selected edges of the 10 MHz clock which
could be done more digitally in a FPGA.

I presume one can pull the existing crystals enough with some hacking
of the oscillator to add a varactor...

This would avoid a non integer frequency setting where the DDS
approach does not (unless you multiply by 3 to 30 MHz first I think).



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] HP 3586 entirely referenced to 10MHz: A solution II

[David I. Emery]

On Sat, Apr 02, 2011 at 04:13:55PM -0400, Chuck Harris wrote:

> Unlike simply stabilizing the BFO crystal as you propose.

Has anyone given any thought to an alternative - phase locking
the original BFO Xtals with a very narrow bandwidth loop to something
derived from the 10 Mhz standard in such a way that the final frequency
of the BFO comes out exact ?   Looks to me (superficially without looking
at the schematic carefully) like this might be possible too...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Coalition to Save GPS

[David I. Emery]

On Sat, Mar 12, 2011 at 01:29:55PM -0800, J. Forster wrote:
> 
> > 2) For this company to have high bandwidth they're going to need a
> > precision time source at each transmitter. Will it be gps??? :-)
> 
> A  sheet of aluminum as a ground plane below their GPS antennas will kill
> a lot of QRM if the GPS is located above their x antennas.


I have little doubt that someone installing a ATC transmitter would
be able to come up with the required steep skirted high stop band attenuation
filters, and as John suggests the correct kind of antenna screens.

But that is not the problem.   The problem is all those folks
without those resources or knowledge with existing gear that wasn't
designed for that kind of RF environment.


> 
> > 3) Wouldn't the most used GPS devices in the US be smartphones (iPhone
> > etc)? Tell those users that location services won't work any more and
> > wait for a reaction.
> 


> Not all mobile devices use GPS for location. Location can be by
> triangulation from cell sites.

It can be, but this is rare.   Most is now assisted GPS.  



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] GPS Usage

[David I. Emery]

On Wed, Mar 09, 2011 at 08:01:31AM +, Poul-Henning Kamp wrote:
> Well, how can you argue with closing a system that was aiding terrorists ?
> 
> The reason LORAN-C got killed was that DoD/DHS couldn't jam it if a
> terrorist with a suitcase-nuke was trying to find his way to Congress.

Is this tongue in cheek, or do you have any actual basis
for stating that DHS was afraid Loran C WASN'T jammable ?

If the later, this is a rather provocative concept... make an
increasingly vital but easily jammed resource the only readily available
means of precision position and time determination so the government (or
some government, or for that matter many private malefactors) can be
sure to be able to reliably deny accurate position and or time to the
public (or  at least many targeted groups within  the public) at will ?

I wonder what the threat analysis behind this one was... making
an increasingly vital service more fragile because of what some have
called "movie thriller" plots ?

Have they really convinced themselves that bad guys CANNOT
figure out a workaround ?   It has always happened in the past...

> 
> Your government money at work...


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] ext ref LNB Re: ADEV

[David I. Emery]

On Mon, Nov 15, 2010 at 06:20:55AM -0800, jimlux wrote:
> Mike Feher wrote:
> >10 MHz locked LNBs do not use a separate connector. Everything goes down/up
> >the single main coax. The typical L-band down-converted frequency and the 
> >10
> >MHz are easily separated, as is the DC. These are definitely not
> >inexpensive. Regards - Mike 
> >
> >
> 
> Ah.. but the question is really not whether the "new" price is cheap, 
> but whether there's some reason why someone would be doing a massive 
> refit, and dumping lots of these on the market surplus.


FWIW, I have purchased C, US FSS Ku and Euro FSS Ku ER 
LNBs on Ebay for well under $100 NOS in box with spec sheets.
Not yet seen Ka ones.   Did buy an X band.

Sellers had a few (eg two or three), never seen large
quantities... but surplus ER LNBs command LOWER prices because of the need
for the external reference and so forth... 

You would, naturally enough need a feedhorn (these are mostly
WR90 for Ku)...

Your pilot tone concept is interesting... I am not sure
how large your array might be and what issues would be involved 
in distributing the pilot tone to it... nor exactly what the 
noise spectrum (ADEV) of a cheapie DRO LNB might look like and
what would be required to generate the necessary LO phase estimates
from the pilot as translated by the unstable LO...


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] ADEV

[David I. Emery]

On Sat, Nov 13, 2010 at 07:01:26AM -0800, jimlux wrote:
> 
> To the Ku-band downconverters..  They're pretty crummy (but have a 
> decent SNR to work with).. however, I've seen that there are two kinds.. 
> a vanilla LNB and ones described as "crystal locked"... both are cheap 
> ($20-30 for the former, maybe twice that for the latter)... what's the 
> difference?  And, getting into time-nuts territory here, where's the 
> reference for the "locked" variety coming from? Up the coax? inside the 
> LNB?  And, can it be retrofitted from a much quieter oscillator?   I was 
> thinking that one could build a radio camera with a small array of 
> Ku-band dishes, if you could lock all the receivers together.  They 
> *are* pretty low noise (20-30K)

There are three kinds of LNBs in common use in the VSAT world...


1.  Open loop unlocked DROs, often with around a MHz or two or
more error due to temperature and calibration and drift over time.  More
expensive higher grade ones are tighter spec'd, but rarely much less
than 250-500 KHz over time and temp.   Most all DTH dishes use these,
often with rather loose frequency specs since the DTH carriers are wide,
fast signals.

2.  Closed loop DROs phase locked to a crystal or I believe
about as common, a UHF or higher frequency oscillator phase locked to a
crystal reference with some degree of multiplication to the final LO
frequency (maybe not much these days with fast prescaler/divider chips).
Crystal in this case is - depending on price - just a plain XO or either
a TXCO or in certain cases a OXCO.   More expensive ones have better
stability specs.Generally these sell for 5-10 times what a cheap DRO
LNB for the mass market might go for.  And can be as good as 1 PPM or
so.

PLL LNBs are mostly used for data or audio transmissions on
narrower, lower  bit rate carriers than TV but also used for many critical
professional TV broadcast and similar applications.

3. External reference LNBs with 10 MHz (pretty universal) going
up the cable that also carries power and brings the L band signal down.
I'm not entirely sure how many of these designs simply bandpass filter
and then limit the 10 MHz and use that directly as a PLL reference and
how many phase lock a VCXO to the 10 MHz coming in.  Otherwise similar
(and often  derived from designs for) the internal reference PLL types
in 2 above.

These ER types are more apt to be used for more exotic
specialized applications where very high frequency accuracy or some
degree of phase coherence  with other equipment or LNBs is useful.

Obviously with the high multiplication factor, one needs a quiet
reference inside the PLL bandwidth (and that is pretty wide to ensure 
reliable lock) - one suspects that issues with degradation due to
mechanically induced noise and phase shift in the cables can be a
problem.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] A little quick advice, please

[David I. Emery]

On Sun, Oct 31, 2010 at 12:25:22PM -0700, J. Forster wrote:
> Two comments:
> 
> I have a lot of Tek 7xxx stuff and almost none of it cost anything like
> $0.50 on the dollar. Virtually everything cost well under $0.10 /dollar.

I would agree... I have rarely seen 80s/90s used TE sell for
more than about 5 cents on the original MSRP dollar... lots is
advertised for more, but look on Terapeak and see how much of that
actually ever sells at those prices.   One assumes the few items that do
sell at those exorbitant prices are either sold to naive newbies  who
don't know better or some company or agency that has the gear written
into a test procedure or installed in a system with specific to the
device software and simply MUST have an exact replacement.   And I darkly
suspect a few sales at high prices are money laundering... or conceal
other shenanigans...


> > Your worries about warrantee are quite valid. But if I can get a used
> > scope or bit of test equipment for less than $0.50 on the dollar of a
> > new one, it's a pretty good bargain for home use. If it is for work,
> > whole different story. That's where the 2236 came in. I was making a
> > living on the road doing field service. It couldn't break or I'd be in
> > deep sneakers. So it arrived new in a box. Of course that was many
> > many moons ago.
> >
> >
> > Bob
> > KI2L


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Maintaining boatanchors

[David I. Emery]

On Sat, Oct 23, 2010 at 02:44:51PM -0700, J. Forster wrote:
> Very true, except it's more like 5-10 years.

These days John is absolutely right... likely none of the
developers, none of the equipment, perhaps not even the corporate
shell of the division or department that designed the product and 
wrote the software survives.   Probably the source code was thrown
out with the old servers that were sold for scrap... or just carted off
to be shredded with all the other paper and electronic records...

Horror stories abound about organizations that need to make some
minor patch or change to source code of a popular product for some
important customer even just a few years after its release and nobody
can find the right source code or the right build environment
(compilers, libraries, OS etc and the hardware they ran on) or if they
can be found it takes many many hours of expensive time and talent to
reconstruct the right stuff to actually make a code image that matches
what is shipping.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Conducting Bench Top Material

[David I. Emery]

On Fri, Jan 29, 2010 at 05:15:51PM -0800, J. Forster wrote:
> To my aging eyes, the flashlight looks distinctly blue-white. I don't know
> how these particular LEDs are built, but the unit is less than a year old.

My understanding is that a lot of high brightness "white" LEDs 
are internally a UV emitting LED junction illuminating a phosphor.  The
light you see comes mostly from the phosphor.

Lighting type phosphors have been around forever in fluorescent
bulbs... and are fairly continuous spectra mostly...

I don't think there is any way of getting broadband white light
out of a LED junction, though of course hybrids of multiple different
color LEDs can be used (and are in the display business).

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] 60Hz mains clocking in computers

[David I. Emery]

On Sun, Dec 13, 2009 at 07:39:05AM +, Poul-Henning Kamp wrote:
> In message <2157.12.6.201.67.1260689371.squir...@popaccts.quik.com>, "J. 
> Forste
> r" writes:
> 
> >I'm not so sure about the Nova 1200. I think all the Novas had the RTC was
> >on a standard I/O board, [...]
> 
> No, it was an option, but almost everybody bought it, because it was
> necessary to run any kind of timesharing kernel (RTOS, DOMUS, etc)

Technically one could order basic IO boards without some of the
functionality - they simply didn't stuff in some of the chips (and more
than one customer just added the requisite chips themselves).   I do
remember that there were some functions on that card that were rarely
stuffed...

I seem to remember that RDOS (the NOVA disk operating system)
DID require the RTC and I certainly don't remember any hacks in the
system code to get around the need for timer interrupts to keep time and
handle delays and timed waits.  It was a real time multitasking kernel,
though only one "process" (mostly) due to the lack of memory management 
Long time ago though...

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] 60Hz mains clocking in computers

[David I. Emery]

On Sat, Dec 12, 2009 at 11:29:31PM -0800, J. Forster wrote:
> I'm not so sure about the Nova 1200. I think all the Novas had the RTC was
> on a standard I/O board, along with the serial interface, PTR, PTP. I
> remember two crystals, one 16.000 KHz for the clock. The other was for the
> Baud Rate generator, somewhere about 1 MHz. A minimal system had 3 cards
> (CPU, Memory, and I/O)

No 50/60 Hz interrupt was standard on any DG machine that I
remember. I do remember some on early DEC equipment.  And yes they had a
Xtal RTC.

I do remember the early DG basic IO boards had a big LF crystal
for the baud rate generation, but I think a later version of the design
used a baud rate generator IC and a much smaller (and cheaper) crystal
or canned crystal oscillator along with a real UART.

OS timing was based on classic real time xtal based interrupts,
not the power line.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] LORAN-C demise

[David I. Emery]

On Sun, Nov 29, 2009 at 12:25:06PM -0800, Mark Spencer wrote:

> The main difference is that receiving lf signals is challenging in
> many areas built up areas and the doppler shift of hf via sky wave
> reduces the accuracy considerably, while there are already a large
> number of exisiting high power transmitters that can be locked to an
> external time base and have line of site paths to many locations in a
> typical metropolitan area.   If a sutiable receiver existed this might
> be a feasible means of distributing accurate frequency info and then
> with a suitable reciever you could generate a 1 pps signal.  That being
> said a dedicated uhf or shf transmiter that could send accurate 1 pps
> signals (as well as providing a very accurate carrier frequency) might
> be an easier solution.  In any event if there was a market for such a
> system I believe it would have emerged by now.   

As I suggested earlier, I believe that relatively simple tweaks
to a broadcast ATSC transmitter/modulator/mux chain to lock both carrier
frequency, symbol clock, and say PCR clock to a local cesium standard
with time of day based (initially)  on GPS would probably be quite
practical and perhaps even little more than using the 10 Mhz (or 27 MHz
derived from it) from the cesium as clock input for existing plant and
setting some firmware settings correctly.

OBVIOUSLY as others have pointed out someone has to pay for this
even though the actual costs might be very small compared to the other
operating and engineering costs associated with the broadcast
transmitter plant.  It is hard to think of a more powerful signal for
time sync in a metro area...

As for receivers, existing ATSC tuner/demod chip sets and a FPGA could
no doubt supply all the usual timing signals (10 MHz, 1 PPS, time of day
in some  standard format).   One imagines sub microsecond PPS accuracy
(once propagation skew is measured) is quite possible.

One would clearly need to use a GPS based measurement to establish
the propagation based skews... 

> I imagine you could even design a gps timing receiver that could also
> receive terristerial signals as a backup, but again it does not seem
> there is a market for this (:

Network effects apply here - if there is no signal to lock to,
then there is no market for a receiver - if there is no receiver even rather
low cost changes to TV plant aren't gonna happen or be justified...

And I suppose the bottom line is that we'd better hope that no
natural (or perish the thought deliberate man made) event takes out
enough of GPS to cause GPS based timing to fail.   And system designers
had better start thinking about very local jamming of GPS timing
receivers at targeted sites that might cause a vital system (say public
safety radio) to degrade or fail.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

[David I. Emery]

On Sun, Nov 15, 2009 at 10:33:07PM -0500, David I. Emery wrote:
> 
>   LORAN C represents a viable (albeit not often deployed) backup
> to time and frequency control and could be implemented in modern
> hardware as a backup location service at reasonably low cost for those
> applications where that is important enough.  

I might add that there ARE some regional solutions to the timing
and frequency backup issue (time-nuts meat) that COULD be implemented
pretty easily. 

One is locking ATSC TV signals to Cs standards backed by GPS. I
am pretty sure that it would not take a lot of effort to adopt existing
ATSC Tuner chip designs and maybe the actual current technology already
available  chips themselves to recover accurate time and frequency from
a ATSC signal locked to a good standard.

And TV transmitters are LOUD compared to GPS and therefor not so
easily jammed on a wide area basis.

I don't imagine the cost of Cs locking a few TV signals is all
that high either... most of the gear can accept external frequency
references and clocks... and already does to a considerable degree.

Obviously if one needs time of day to high precision one needs
to use a local GPS to determine the time offset of a TV signal as
received at a particular site, but this should not change much provided
the clock at the transmitter was really good.   And the ATSC transport
stream provides a rich channel for sending information about time offsets
and other sync status on a real time basis... 

I suppose this could substitute for Loran as a regional backup
for telecoms networks as protection against GPS denial...

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

[David I. Emery]

On Sun, Nov 15, 2009 at 07:17:37PM -0800, J. Forster wrote:

> There were, of course, no map or chart displays. Imagine what 20+ years of
> development would have brought.

E Loran could supply the same basic position information as input
to charting and mapping software as GPS does... most of the code doesn't
care where the position came from one wit

But I am sure you know that (we are in violant agreement).


> -John
> 

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

[David I. Emery]

On Sun, Nov 15, 2009 at 08:56:36PM -0600, Didier Juges wrote:
> 
> I don't disagree that it would be fairly easy to disrupt the consumer
> devices, but other than a few missed appointments and frustrated gadget
> freaks, and the occasional emergency vehicle not finding its way to the
> scene of an accident, that would be more of a problem) I am not too worried
> about the consequences of that.

GPS has been widely used for time and frequency sync in radio
systems of various sorts - some depend on it for successful simulcast
from multiple transmitters (including many public safety radio systems)
and while there is SUPPOSED to be significant holdover, there is are
always those situations where nobody has EVER checked that it works...
And what will holdover do about LONG TERM outages of GPS ?   Perhaps 
folks are willing to bet the whole infrastructure on the supposition that
we could NEVER see a complete long term loss of signal (using civilian
receivers with modest anti jam abilities) in a particular location or
region - I am not exactly sure what alternative might exist though I
guess there are some for time and frequency - terrestrial GPS beacons
from high points that could lock up a cell system in a region come to
mind...

And more and more and more stuff depends on more or less
ignorant and sometimes not very bright operators expecting that the GPS
positions are always there or they don't know what to do.   And if GPS
is almost always reliably there there may well be little or no practical
training about what to do if it fails.   Failure modes and paths in code
and procedures (and sometimes even actual hardware) which aren't often
tested or exercised usually fail when actually needed and often in
entirely unanticipated ways - maybe the backup ALSO depends on GPS in
some way the system designers never thought about (or knew could
happen)...

LORAN C represents a viable (albeit not often deployed) backup
to time and frequency control and could be implemented in modern
hardware as a backup location service at reasonably low cost for those
applications where that is important enough.

> 
> The thread started with the loss of the LORAN system, and nobody (maybe I am
> going out on a limb here) ever used a LORAN receiver in his car to find the
> nearest restaurant :)

Actually readers of this list have, though not in recent times I guess.
> 
> I think the people who should complain the most about the loss of LORAN are
> the boaters, but they are the one who embrassed GPS the first and are it's
> biggest advocates!!! I know, I live on the coast of Florida.

An enhanced LORAN that has some of the accuracy and automation
of a GPS receiver exists... I suspect boaters care most about
convenience (and accuracy) and found GPS easier.   Certainly so compared
to earlier LORAN C gear.

And of course there is another issue with GPS, it is controlled
by the DOD and is supposed to have the ability to deny service in a
region if conditions are sufficiently apocalyptic to require it.   For
folks worried about this (more outside than inside the US obviously)
LORAN is a local resource they may control and certainly can if they
make a more or less modest investment in the ability to do so.   Some
(large) players are of course planning their own space based systems for
just this reason but LORAN can be implemented by most nation states...

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

[David I. Emery]

On Sun, Nov 15, 2009 at 08:22:50PM -0600, Didier Juges wrote:
> I think the problem with the Monterey Bay jammer was that he was jamming the
> DGPS correction signal, not the GPS signal itself. The DGPS correction
> signal is sent over the UHF band. Most marine GPS are DGPS because they need
> the better resolution it provides, particularly to find buoys and channel
> markers in the fog. The DGPS correction signal does not benefit from the
> spread-spectrum modulation and associated jamming resistance of the GPS
> signal itself.

That is the first I've heard of a UHF DGPS correction transmission
can you provide a frequency and modulation mode ?Most I know of are
re purposed LF NDBs or similar transmitters in the 200 to 400 KHz or
so range that transmit a PSK'd carrier with the DGPS data at fairly low
speed on it.

I have heard of cases of wide area GPS outages noted by many
folks with NON DGPS receivers (DGPS receivers  mostly will just indicate
no DGPS available and still show a pretty good position) that were
caused by UHF signals on the L2 frequency... though I am sure there are
incidents of accidental interference to LF or other distribution of
DGPS.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Reference oscillator accuracy

[David I. Emery]

On Fri, Nov 13, 2009 at 09:51:11AM -0800, J. Forster wrote:
> WWVB not WWV.
> 
> IMO, WWVB is MUCH fussier than LORAN. It's just utter stupidity that LORAN
> is being shut down.

I have emailed my brother in law who is a rear admiral (I think
now called a vice admiral) and currently CFO of the USCG (and as a note
re your alma mater a MIT Sloan grad) and rather loudly said so myself.  
He most likely was part of the group that made the decision... I intend
to ask him why they did it when I next see him.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] OT: Spectrum Analyzer

[David I. Emery]

On Fri, Oct 30, 2009 at 11:39:37PM -0400, Glenn Little WB4UIV wrote:
> Keep in mind that anything much newer than the 141T will have custom 
> parts and processors.
> This makes the instrument smaller and more versatile, but, less repairable.
> The 141T is a workhorse.
> 
> I would not trade mine for any number of the processor controlled analyzers.
> Having a nice clean analog display is nice and you do not have to 
> worry about did I get an accurate display of what I am looking at or 
> did what I am looking for occur between sample on the digital display.
> 
> I hope you find what you are looking for. It is hard to beat the 141T 
> for a spectrum analyzer.

I disagree.   Modern analyzers have a LOT of features the 141T
family lacks - starting I guess with full frequency synthesis for near
time nuts level frequency accuracy (most all take external 10 MHz from a
standard and are fully coherent with this).This makes a REAL
difference if you are interested in observing and analyzing unknown
signals... and allows the analyzer to also serve as a (microwave)
frequency counter.   If you are observing a crowded part of the
spectrum, having say 5 MHz or so frequency accuracy (typical of
unsynthesized instruments at VHF and above)  doesn't cut it AT ALL...
gets to be completely impossible to reliably identify a particular weak
signal or spur with 50 others nearby.

And frequency synthesis also allows precise keypad entry of a
frequency of interest (or via GPIB or other remote control)... try that
on an analog only crank the dial instrument.  At best you will do a LOT
of dial cranking...

Another feature less pre-Cambrian analyzers have is markers...
allowing accurate measurement of level and frequency at a particular
point on the screen, and often differential measurement too (eg so many
db down). Most instruments with markers will also do auto-peak search so
you can find the next left or right peak and read its frequency and
level with one key press.   And usually the marker readout of frequency
and level is significantly more accurate and higher resolution than the
display can be read easily... and often more than one marker is allowed
on screen at once.

And yet another feature modern analyzers have is digital display
memory - which makes it usefully possible to make slow narrow band
measurements with say 100 Hz or  30 Hz bandwidths.   Really antique
analyzers had display storage tubes or similar arrangements as options,
but all even slightly modern ones have fully integrated digital storage
and displays.

And yet another feature that present in all modern instruments
is peak hold, and usually also valley hold... allowing one to look over
time for elusive signals that appear only momentarily, or see how strong
or weak the noise or some signal got in a particular time interval.

Most modern instruments also include extensive self check and
auto-calibration firmware which can compensate for drift and aging of
the various analog circuits and handle temperature and other
environmental changes much better than older instruments without it.

And modern instruments have as at least as an option (usually
installed) some form of remote control allowing software to access the
measured data and control the analyzer - making possible all kinds of SW
applications that process measurements into more useful forms and
perform various corrections. GPIB is very common here.

Another feature absent in 141T era analyzers is plotting or
printing the screen via a printer of some kind (or these days a printer
emulation program such as the excellent ones John Miles provides).  
This allows capture of a  fully annotated screen image (these days as a
.png file)...

Really modern instruments (last 10 years or so) also often have
FFT processing for fast narrow band analysis and modulation domain
analysis including digital demodulation and constellation and error
vector displays.

And many more recent instruments have built in firmware
measurements of things like occupied bandwidth and noise power per root
Hz... this all can be done with an attached laptop, but it is nice to
have it integrated and available with a button press.

It is true, of course, that the more recent the instrument the
more likely it is to have at least some proprietary parts that are
probably unobtanium by the time the instrument hits the affordable
surplus market.   And unfortunately many really modern instruments do
not have easily obtained schematics and chip level documentation
available - this alas being true of most T+M gear made recently, not
just SAs.   But lots of instruments with all the features I have
described above that date from the late 80s through 2000 or so are
readily available in your under $3K price range now and ARE documented
by available service manuals and schematics.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
0

Re: [time-nuts] Lady Heather and gpsd

[David I. Emery]

On Sat, Oct 17, 2009 at 09:44:12PM -0400, Tim Cwik wrote:
> 
> I would like to use gpsd to provide time information from the Tbolt to 
> ntpd on one of my servers but I would also like to be able to monitor 
> Tbolt operations with Lady Heather. I am planning to make a splitter for 
> the rs-232 from the Tbolt, connecting TD and RD to the server running 
> ntps and TD only from the Tbolt to a machine running LH. Will this work? 
> Is this the best procatice for doing this?
> 
> I suppose another answer would be to modify gpsd to do the same work 
> that LH does or arrange for gpsd to pass info packets on to a Linux 
> process doing the same sort of monitoring tha LH does, but this seems to 
> be re-inverting the LH wheel.

I imagine one could hack gpsd to accept and relay commands and
responses from another program (Heather) to a Tbolt out a second serial
port (or the virtual equivalent perhaps).

And perhaps the same thing could be done to Lady Heather itself,
which in certain senses might make more sense for this situation - as
Lady Heather is highly tbolt specific and it might be easier to use
logic in it to sort out the non-Heather commands and responses and pass
them on without getting confused about what it was seeing and doing.  
Not clear what the ideal path to gpsd might be ... I think of some sort
of socket interface rather than a second  physical COM port.

I suppose it is even possible to have Heather just have a
gpsd/ntp mode where it sets up the Tbolt to generate the right stuff and
keep spitting it out and gpsd could merely be a passive listener tied as
you suggest with a simple Y cable.   Depends I guess on how general one
wants to be and what gpsd features one might want to use.

Naturally some thought about conflicts between commands from the
two sources and what the presumed state of the Tbolt is moment by moment
is needed... 


> 
> Thanks for any thoughts,
> 
> Tim N2LTQ
> 
> 
> 
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  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Anyone know a portable way of getting seconds since epoch?

[David I. Emery]

On Tue, Oct 13, 2009 at 10:14:56PM +0100, David Kirkby wrote:
> 2009/10/13 Poul-Henning Kamp :
> > In message <286f7bad0910130703v6680affbx95905a440...@mail.gmail.com>, 
> > David
> >  Kirkby writes:
> >>I've asked this on comp.unix.shell, but never got a 100% satsifactory
> >>answer. Perhaps someone here might know.
> >>
> >>Does anyone know how to get the number of seconds since 1/1/1970 on a
> >>Unix system using the shell - not compiling C code. I can't assume the
> >>computer has perl, python or a C compiler.
> >
> > On FreeBSD you can use the strftime facility in date(1):
> >
> >        $ date +%s
> >        1255442977
> >
> > Poul-Henning
> But it does not work on Solaris or HP-UX

FWIW it works on Darwin (MacOS X) which is BSD derived...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] Why would I want a rubidium

[David I. Emery]

On Mon, Oct 05, 2009 at 12:35:17PM -0700, J. Forster wrote:
> 
> My main gripe w/ Rb and especially Cs is they have very limited lives.
> IMO, it's just not worth paying extra money for stability I don't need. If
> I ever do need their capabilities, there are several on the shelf, but
> until then they can sit unpowered.

The telcom grade (LPRO and similar) Rb's that show up cheap are
supposedly designed for 20 years life continuously operating... and some
have only a few hundred hours on them or less when surplussed.  They
should typically last 10-15 years at least in continuous home lab
service and given their price these days the electricity to power them
for that time interval is much more money than the hardware.

Cesiums have REALLY expensive tubes with limited life, but on the
other hand I understand the tubes don't like to be kept turned off... they
deteriorate when sitting on a shelf and may not recover.




-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] GPS from a window seat

[David I. Emery]

On Sun, Oct 04, 2009 at 03:06:12PM -0500, Bill Hawkins wrote:

> See Joe Mehaffey's list of airlines at
> http://gpsinformation.net/airgps/airgps.htm
> The list of airlines that allow GPS have the caveat that the Captain has the
> final decision.

It is interesting that American is listed as banning them as of
October 2009 (apparently they have switched back and forth on this
policy)...

The list of banned devices did not include them when I checked 
it in August before using my GPS... would at least help if they had their
rules (they tell you to check) up to date.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] GPS from a window seat

[David I. Emery]

On Sun, Oct 04, 2009 at 09:14:29AM +, Robert Atkinson wrote:
> Hi,

> This is correct. There was also an issue with harmonics from the local
> oscillator in the aircraft's own VHF nav/comm receivers blocking the
> GPS. The answer is a 1575MHz notch filter, e.g.
> http://www.edmo.com/index.php?module=products&func=display&prod_id=18006

I have not (not being involved in avionics professionally) heard
of any problems with GPS receivers causing interference to other GPS
receivers or other avionics ... I would be interested in your comments
on whether you know of any such issues and what the mechanisms are.

Obviously I - and I think most anyone on this list - would never
consider doing anything or using any equipment that might endanger an
aircraft (especially one I am flying on, needless to say) - so I have
tried to keep aware of any issues that might remotely exist with
handheld GPSes on planes.


> Another problem was bias oscillators in tape players, these could
> interfere with Omega/VLF receivers. Not a problem now of course. While
> on the subject of Omega/VLF If you come across a Global GNS-500A OEU
> box, it has a Efratom FRK Rb in it. There is one on ebay at the moment,
> item 150257671674, but the price is way to high.

I had heard of that, I know many cheap tape recorders radiate
enough to be detected at some distance - this has been used in the past
by TSCM specialists to find covert planted recorders.

> It's very had to predict interference on aircraft. While the
> probability is low the consequences during take-off and landing are
> severe. Hence the total ban on electronics during these flight phases.
> The "illegality" is endangering an aircraft, however you do it. Avionics
> design is my day job.

I have read that there have been studies with a spectrum
analyzer system on planes that have shown that compliance with the no
radiating device rules and electronics off during takeoff and landing is
far less than 100% though I certainly would not personally deliberately
violate the law whether or not the probability of it causing a problem
is significant.  Apparently one or two cellphones can be seen registering
with cell systems during takeoff and landing on many flights - probably
most of them unintentionally left on.

Publicly discussed and documented cases of interference causing
serious problems are fairly rare... it is unclear how many actual cases
there have ever been.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] GPS from a window seat

[David I. Emery]

On Sun, Oct 04, 2009 at 12:20:26AM -0700, Hal Murray wrote:
> > Why the ban on AM/FM receivers? 
> 
> I assume it's EMI from the local oscillator.
> 
> Is anybody shipping an AM/FM radio that isn't superhet?


FWIW, I have read and been told that there was an era when some
cheap AM/FM radios put out a lot of signal from the LO 10.7 MHz away
from FM stations and that at least a few of them used high side LOs
which would put that LO signal potentially right in the middle of the
band used by VOR navigation beacons and ILS localizers... just above the
FM band from 108-118 MHz.   This would obviously not be good if the
signal power was great enough to interfere with navigation receivers.

The broad rule was put in place because there was no effective
way of determining if any particular radio a passenger might have
radiated or if it even had FM tuning capability.  It was safer just to
ban everything because of those few radios that were way outside of
spec.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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Re: [time-nuts] How do US TV stations disseminate time to DTV converter boxes?

[David I. Emery]

On Thu, Oct 01, 2009 at 08:11:42PM -0600, Greg Burnett wrote:
> 
> How do US TV stations disseminate time to DTV converter boxes? ...And is 
> this time derived from GPS data, or???

There is a time of date message stream (TDT) defined for MPEG
transport streams and that and a slightly different version of in the
ATSC variant of MPEG used by US TV stations transmitting digital signals
(now essentially all of them except LPTVs).

Where the data in this comes from depends on the station. Mostly
it originates either in a transport stream multiplexer that feeds the
ATSC modulator or in a separate system that generates PSIP and other
information (a PC perhaps or a dedicated box)... 

Both the mux and the PSIP generator likely have the usual
battery backed up clock calendar chip as their default source of time of
day but can be configured to lock this to other time sources within the
station.

Depending on how careful the station is about setting this up it
can of course get unlocked and drift or even set to the wrong time zone
offset or daylight savings versus standard time.

Stations may have their entire plant time and frequency locked
to a GPSDO or Rb or Cesium, but there is no FCC requirement for anything
remotely close to that level of accuracy so many don't.   And stations
may lock time codes and timing of  genlock black burst references to GPS
or may not... and may lock the mux time of day to those or not... 

I think the likely explanation of the recent time problem with
converter boxes in the midwest is some common piece of software and/or
hardware used by a number of stations that has a plain old bug with its
timekeeping... 

It is true that one network (Fox) supplies more of the over the
air ATSC transport stream than the others (the rest simply send MPEG2
video and audio signals which are decompressed by the satellite IRD and
then re-compressed for the local air by local station equipment - Fox
supplies more or less the exact compressed audio and video the station
is required to transmit on its main channel and controls the device that
makes alterations to this (like inserting a local station logo) from its
master control center.   It is remotely possible that this means that
some of the time of day info for Fox stations originates with the
network or the network controlled splicer device and the network screwed
up and caused a whole region of Fox stations to transmit the wrong time
of day.

Older analog NTSC stuff had an optional vertical blanking
interval messaging system that was used by PBS stations to transmit time
of day and program guide information and many VCRs and DVRs  and some
TVs can look for and find this signal in the vertical blanking interval
of a PBS signal and use it to set time of day.   PBS stations have a box
that generates this data stream and insert it... and depending on
funding and how careful they are it may or may not be locked carefully
to an accurate time source.

I am not sure if it is currently done, but it is possible to
configure MPEG encoders and mux gear to pass these vertical blanking
interval lines in a digital signal including HD versions and some PBS
stations (or even most all) may carry a digitized version of the same
old VBI time data, as they definitely do carry closed caption data in the
VBI for older TVs...



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."


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