Re: [time-nuts] finding time astronomically , Part 2

[Jim Lux]

On 1/23/12 3:27 PM, Brooke Clarke wrote:

Hi Jim:

I spent quite some time on looking at ways to optically tell the time, see:
http://www.prc68.com/I/StellarTime.shtml




Oddly, I was *just* looking at that page...I mean, I closed the browser 
and opened mail and saw your email.



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Re: [time-nuts] finding time astronomically.

[Jim Lux]

On 1/23/12 6:07 PM, J. Forster wrote:

I think you'd want a slit, not a pin hole.  The pin hole would be
better but it would only work one day a year.


Actually two days per year, unless it was adjusted for the summer or
winter solstice, then it'd be one.



Accompanied by robed assistants chanting ethereal rhymes, we align the 
pin hole at the solstice.  In such a way we will achieve the very 
11-ness of timing. We must, of course, enclose it to make sure that it's 
not crushed by dancing dwarves.


(couldn't resist)

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Re: [time-nuts] Determination of the placement of the first pps

[Jim Lux]

On 1/23/12 5:50 PM, J. L. Trantham wrote:

Is this, in any way, related to the fact the Earth has a Moon?

Ideally, the Earth rotates around the Sun and the Moon rotates around the
Earth.  However, is it better described as the 'center of mass' of the
Earth/Moon


barycenter is the term

 rotates around the Sun?  Not to mention all those other

confounding variables such as other planets and moons?


Well, yes.. there are fairly sophisticated numerical integration 
programs that figure all this stuff out, if you're interested.






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Re: [time-nuts] establishing your position w/o gps

[Jim Lux]

On 1/24/12 9:48 AM, Chris Albertson wrote:

If you want to try your hand at position determination in the pre
radio nav days you can buy a "studen sextent"  It's a low cost plastic
instrument sells for about $60.
That's the Davis Mark 3 (which is basically a copy of a lifeboat 
sextant).  $50 from starpath.com (which also has the more expensive mark 
15, and others)


Or get a copy of "Emergency Navigation" by David Burch, and you can make 
your own instruments from materials close at hand.


All the sight reduction tables and such are available online for free 
now. (although a paper copy is nice, and fairly cheap, being a 
government publication. )


 Better ones start at $200 with $500

to $800 for a good one.   But it required much pratice and training to
outgrow the plastic instrument.I took the class.


It's not that hard to learn yourself, once you get the right conceptual 
model.  The trick is knowing how to use the sight reduction tables.  (I 
figure that if your GPS has died, so has your calculator, so you'd 
better be able to do it with pencil and paper).


I haven't gone to the extreme of calculating the trig functions by hand 
(wasn't that what Napier's wife did.. calculate log tables by hand 
during long sea voyages)


I think you could probably do some interesting 
compass/straightedge/protractor kinds of geometric constructions to do 
sight reduction as well.


Doing a fix on land, in one place, is pretty easy.  (Much easier than 
standing on the deck of a boat that is moving).  The only trick is 
having an "artificial horizon" that doesn't move.. A pan of liquid works 
nicely (molasses, thick motor oil, or corn syrup are your friends. 
Water is bad.. ripples in the least wind)


Star sights are a bit trickier, just because the stars are dimmer and 
harder to find. And seeing the horizon at night is also tough.


 I think most

anyone who wants to sail on the ocean had better take the class just
in case their GPS fails.   I know some one who had both his primary
and backup GPSes fail and he was still a week from Hawaii.   They had
to revert to the old techniques from the 1700's


And hey, you can learn while you're on the way, like Jack London did, on 
his way to Hawaii.  Read "the cruise of the snark" (Project Gutenberg)




Much of pre-GPS position determination is not about finding your
latitude and longitude.  That is a modern notion.What they did and
what sailors still do is find a "line of position".






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Re: [time-nuts] establishing your position w/o gps

[Jim Lux]

On 1/24/12 9:46 AM, Attila Kinali wrote:

On Tue, 24 Jan 2012 11:05:58 -0600
"Lee Mushel"  wrote:


If you're looking for a really interesting topic to read about, the
development of an accurate ship-board clock is really fascinating!   And it
wasn't done overnight!


If you have a few references on books to read, you shouldn't keep them
for yourself ;-)


Dava Sobel's book is good.

The Great Arc by John Keay also has useful information on this kind of 
thing.


the Institute of Navigation (ION) has an $50 CDROM of almost 300 
celestial navigation papers (http://www.ion.org/shopping/begin.cfm  look 
down at the bottom) Lots about timekeeping, etc. in there.


(got that one loaded on the iPad for long plane trips)

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Re: [time-nuts] establishing your position w/o gps

[Jim Lux]

On 1/24/12 10:26 AM, Chris Albertson wrote:

have you ever tried to measure an angular distance using a hand held
instrument while standing on the deck of a moving boat in the open
ocean?  try it and you will see why they wanted a clock. You
really can't measure an arc minute reliably we should expect about 15
arc minute accuracy if you are standing on a moving ship.  A few very
skilled people could do better.

The moon moves what? about 10 degrees per day so in practical terms
you can get time to about 30 minutes.   But other sources of error
would add to that.   But still knowing even the hour is very good
that puts you in the correct time zone



you can do much better than that by looking for occultations (and they 
work with the new moon as well).  If you know what day it is, you know 
about where the moon is, and you can look up in a table which stars get 
occulted when.  Then you just watch through binoculars.


I'd say you can get within ten seconds without much trouble, assuming 
you can find the star.






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Re: [time-nuts] establishing your position w/o gps

[Jim Lux]

On 1/24/12 3:19 PM, J. Forster wrote:

Is the USNO almana/ephemeris still published in hard copy every year? That
had moon timing, etc.



You can download pieces from the Astronomical Applications website at USNO.

Or you can buy a copy of the Nautical Almanac for about $20 from a 
variety of sources.  You could also download the pdf (but printing it 
would cost you more than the $20)..


Amazon has it, for instance.

http://www.usno.navy.mil/USNO/astronomical-applications/publications/naut-almanac

will find it, but the GPO version is more expensive than the commercial 
versions..



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[time-nuts] telling time without a clock

[Jim Lux]

OK.. without getting into celestial navigation, the whole thing of 
telling time with the moon is intriguing.  And with some forethought and 
data available today, we could fairly easily do what folks back in the 
18th century could not.


Let's say you run a suitable celestial model and identify all the 
reasonably bright and identifiable star that the moon occults in a given 
day.  The moon moves about 1/2-1 degree per hour against the star field, 
so the question is, could you find, say, a star every couple hours.


Then, assuming you know *about* what time it is, say, 930PM, you can go 
to your table, see that the Moon occults zeta obscuris at 2143.  You sit 
there with your binoculars and watch the moon, and when zeta obscuris 
disappears, you know it's 2143.  Done.


You could even do it automatically with a not very accurate "goto" 
telescope and a camera (you just have to be able to point to the correct 
limb of the moon and look for the star).


This kind of search would be incredibly tedious if you didn't have 
automation to help, but today, with reasonably accurate star catalogs 
AND reasonably accurate numerical ephemerides, it should be possible to 
make a "time almanac" with a page for each day, etc.



(obviously, this only works about half the day, when the moon is up)

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Re: [time-nuts] telling time without a clock

[Jim Lux]

On 1/25/12 8:38 PM, Jim Lux wrote:

OK.. without getting into celestial navigation, the whole thing of
telling time with the moon is intriguing. And with some forethought and
data available today, we could fairly easily do what folks back in the
18th century could not.

Let's say you run a suitable celestial model and identify all the
reasonably bright and identifiable star that the moon occults in a given
day. The moon moves about 1/2-1 degree per hour against the star field,
so the question is, could you find, say, a star every couple hours.

Then, assuming you know *about* what time it is, say, 930PM, you can go
to your table, see that the Moon occults zeta obscuris at 2143. You sit
there with your binoculars and watch the moon, and when zeta obscuris
disappears, you know it's 2143. Done.

You could even do it automatically with a not very accurate "goto"
telescope and a camera (you just have to be able to point to the correct
limb of the moon and look for the star).

This kind of search would be incredibly tedious if you didn't have
automation to help, but today, with reasonably accurate star catalogs
AND reasonably accurate numerical ephemerides, it should be possible to
make a "time almanac" with a page for each day, etc.


(obviously, this only works about half the day, when the moon is up)



And, you should be able to make it work on any planet, as long as it has 
moons (and you have the ephemeris known well enough.. not guaranteed by 
any means)


Further, it occurs to me that if you know exactly what time it is AND 
you know the elevation of the moon and the star it's occulting, you know 
your lat and lon.  I think..


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Re: [time-nuts] telling time without a clock

[Jim Lux]

On 1/26/12 10:14 AM, Chris Albertson wrote:

On Wed, Jan 25, 2012 at 8:38 PM, Jim Lux  wrote:

OK.. without getting into celestial navigation, the whole thing of telling
time with the moon is intriguing.  And with some forethought and data
available today, we could fairly easily do what folks back in the 18th
century could not.

Let's say you run a suitable celestial model and identify all the reasonably
bright and identifiable star that the moon occults in a given day.  The moon
moves about 1/2-1 degree per hour against the star field, so the question
is, could you find, say, a star every couple hours.


If you have a telescope and you can measure where it is pointing
relative to the local meridian, then you don't need the moon.  You can
use a fine wre in the optical path an watch for when a star crosses
the wire.  The advantage of this is the telescope does not need a
tracking motorized mount.  It can be fixed to a concrete pier.Even
a modest scope in the city can see hundreds of stars per hour.



I was thinking of something that works anywhere in the world (pretty 
much) with things that you can hold in your hand (the table and your low 
power scope/binoculars).


In theory, if you knew approximate time (say to a minute or so), then 
you wouldn't even need to find the star.. Look for the moon, the star 
will be right next to the limb, and wait til occultation occurs.






Using the Moon is only useful if you can't measure where the scope is
pointed.  The Moon provides a good, well known reference.


And easy to find in the field.


 So for a

portable setup it could work best but there is a built-in problem with
the Moon, you may not have good data on the shape of the limb.
Mountain ranges and valleys between peaks are different depending on
your location on Earth.  If you move even a mile your star might hit a
different place.In fact people have used Lunar occulations to map
the height of lunar mountains.Another effect is diffraction.  The
stars don't just "wink out" because they do have a finite diameter
People have actually used the moon to measure the diameter of stars by
accuratly measuring the defraction effects.   But the project had
problem because of large boulders and mountains on the moon made it
hard to know the orientation of the "knife edge" and worse, this would
chane if you move just a few feet, some different boulder might be
there.


This is a very good point.. what sort of effect are we talking about. 
The moon subtends roughly 1/2 degree, 30 min of arc.  What fraction of 
the lunar diameter are these mountains?  Say, 10km high out of 3400 km 
diameter, so one part in 340, or roughly 1/10th minute of arc


1 degree = 4 minutes of time, so 1 minute of arc is 4 seconds of time.

Those hills and rocks are on the order of the 1 second time measurement 
uncertainty.





Another idea that maybe is even better is to use radio observations
with two antenna that have a very long east/west baseline.   You watch
the difference in phase to a distant radio source.   As the phase
different passes zero you know it just went overhead and then the time
would have to equal the R.A. of the radio source.   Problem is the
physical length of the cables you'd need to lay out and the lack of
really bright radio sources.   In theory one could get arbitrary time
accuracy this way.A few radio source are "easy" to detect with
affordable surplus/ebay equipment.



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Re: [time-nuts] GPS tick all over the place. Suspect aurora effects

[Jim Lux]

On 1/26/12 2:08 PM, paul swed wrote:

We are talking parts in the -9th but I am using a hp3801 and the general
software that lets you see the 1 sec variation.
I had never seen this behavior before and thought the oscillator must be in
trouble. Measured it against a local RB and it was stable.
Then it hit me, could this actually be the effects of the aurora?
I am thinking it just might be.
Regards
Paul
_


google for "Space Weather Effects on GPS"

there's a presentaton by Thomas Bogdan at the Space Weather Prediction 
Center that gives you some numbers to work with.


10s of meters effects aren't unusual.

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Re: [time-nuts] telling time without a clock

[Jim Lux]

On 1/26/12 2:55 PM, Jim Palfreyman wrote:

As a reasonably experienced occultation observer (and the very reason I got
into being a time-nut - so I could time these observations), the main
problem is that the number of binocular-observable occultations is actually
quite rare. When the star appears or disappears behind the bright limb it
is actually hard to see - even if the star is very bright. When the moon is
nearly full, even disappearances behind the dark limb are hard.


Yes, that's what I observed when I was trying it a while ago..



So ideally you want bright star disappearences on a dark limb with a moon
before first quarter. (Last quarter as well - but then it's a reappearance
and you don't quite know where to look).


that would sort of limit you to 1 week out of 4. But better than 
nothing, for a technique that requires no outside assistance.




This limits the number of bright stars quite drastically. And then you have
clouds...



Yeah, that is something I don't have a feel for.. How many stars are 
candidates? I assume you could get a moon RA/declination list, and then 
run that against the star list.


 This is one of those things that  I was hoping there's probably 
someone who has a program that can do the search trivially.


I have a moon ephemeris, but I haven't found a convenient star catalog 
(something in ASCII that has ID, RA, Dec, Mag would be nice)




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Re: [time-nuts] telling time without a clock

[Jim Lux]

On 1/26/12 4:35 PM, Jim Lux wrote:


Yeah, that is something I don't have a feel for.. How many stars are
candidates? I assume you could get a moon RA/declination list, and then
run that against the star list.

This is one of those things that I was hoping there's probably someone
who has a program that can do the search trivially.

I have a moon ephemeris, but I haven't found a convenient star catalog
(something in ASCII that has ID, RA, Dec, Mag would be nice)



OK.. I found something.. A list of the 301 brightest stars (down to 
about 3.55 mag)..
Bummer.. only about 5 or 6 of them are anywhere near where the moon goes 
in 2012.  (as in within a few degrees in declination)


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Re: [time-nuts] Prologix GPIB-ETH - Linux examples ?

[Jim Lux]

On 1/31/12 12:34 PM, cfo wrote:

On Mon, 30 Jan 2012 19:23:10 +, cfo wrote:


I just got my Prologix GPIB-ETH

I am 90% Linux Ubuntu based , and would like to get 99% based. So i am
looking for some C code examples, implementing the linux networking
part.



Thanx for all the suggestions , i'll have a look at porting winsock apps
to sockets.

But i really like PHK's pylt , and will prob. give a prologic-eth driver
a try.
I have never tried python , but i hope i can ask for help "on the net".

After all i do have PHK's USB py driver as a nice skeleton.

CFO



Python is easy, once you get past the "indenting for block structure" 
thing..


It's a great way to do scripting.

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Re: [time-nuts] GPS SDR

[Jim Lux]

On 2/1/12 9:27 AM, Chris Albertson wrote:

On Wed, Feb 1, 2012 at 8:19 AM, Attila Kinali  wrote:

On Wed, 01 Feb 2012 09:07:23 -0500
John Ackermann N8UR  wrote:


There've been numerous threads on the Gnuradio mailing list about code
to receive GPS using the Ettus Research USRP hardware.  I don't know
whether anyone has actually made it work, but it appears that it's been
the subject of quite a few academic projects.


That is the problem with an academic projects typically something like
this would be part of a Master's theses or a senior project.  and then
the student graduates and was no more interrest in supporting it.

I thought it might be interresting but then found out you need to buy
$2,000+ worth of hardware for even start experimenting.Open Source
SDR needs to run on a common affordable platform or it will never gain
the critical mass of users that it take to make the project live
longer then a few months.

I think the way to go is to find a commercial GPS chip that has a low
level interface and then build the uP controller using a common
development system.   Both the chip and the uP board need to be,
common, well documented and cheap.   Then with this you build an open
source thunderbolt type device. An SDR that samples the microwave
RF is going to be un-affordable, even mixing and down converting
microwaves is not so simple as doing the same on HF ham bands.  But
there might be low level GPS chip available for cheap.



Actually, most of the JPL GPS receivers do direct sampling from RF with 
a single bit converter. You need about 100dB of gain from the antenna, 
with some filtering (to get L1 by itself), and then you run it into a 
limiter, and just sample the output at around 40 MHz, run it into an 
FPGA, and do your stuff.


No superhet, no mixers, no nothing.  It's only 1.5 GHz.. these days, 
that's not particularly exotic.


http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41781/1/11-0046.pdf 
gives some hints on the hardware side.









From my experience the only way projects like this get started is one

guy works until he has a demo of a proof of concept and can say "Hey
look this sort of works and can do simple things" and then others join


Yep

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Re: [time-nuts] GPS SDR

[Jim Lux]

On 2/1/12 10:12 AM, Attila Kinali wrote:

On Wed, 1 Feb 2012 09:27:30 -0800
Chris Albertson  wrote:


I thought it might be interresting but then found out you need to buy
$2,000+ worth of hardware for even start experimenting.Open Source
SDR needs to run on a common affordable platform or it will never gain
the critical mass of users that it take to make the project live
longer then a few months.


That's because the URSP is a general purpose system. It is designed
to do many things. That makes it expensive. And being expensive,
it has a low production volume, which makes it even more expensive.

I think, a specialized GPS SDR can be build for less than 500 USD
in low (a dozen at max) volumes.

I guestimate, that the RF/ADC part would cost somewhere between
100 to 200 USD in parts. The big uncertainty here is the FPGA.
I have no clue how much logic space for a GPS SDR would be needed
at minimum and how much would be desirable. Hence i have no guess
what the FPGA would cost (could be anything from a cheap 20USD
FPGA to a 300 USD one).




how many channels do you want to track at once?
I can tell you that you can track at least 12 channels simultaneously 
with single bit ADC sampling at around 40 MHz in a pair of  Virtex II 
3000 parts. You might be able to do better (I don't know how full the 
two FPGAs are).  (that's the published spec for the radio we're flying 
on the SCAN Testbed on ISS)  It's actually a L1,L2,L5 receiver, but, of 
course, the tracking loop is the same for all frequencies, whether you 
track 12 S/Vs in L1 or 4 in all three channels.. it's all the same.


You'll have to do the nav solution in some sort of other processor.. 
that's just running the tracking loops and generating raw observables.


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Re: [time-nuts] GPS SDR

[Jim Lux]

On 2/1/12 12:22 PM, Attila Kinali wrote:

On Wed, 1 Feb 2012 11:49:51 -0800
Peter Monta  wrote:


One possible inexpensive design:

- RF input passively split three ways, with LC filters for the three
channels:  L5/E5, L2, and L1/E1/Glonass
- For each channel, a downconverter (Maxim MAX2121) feeding a ~65 Ms/s
ADC (e.g. MAX19505)
- A low-cost FPGA (e.g. Spartan-6) that quantizes the channels to 2
bits, does AGC, assembles Ethernet packets
- Ethernet PHY, power (PoE?), etc.



You don't need the ADC: you just need a limiter/comparator. But you do 
need a bunch of RF gain.  I think you can get suitable ceramic filters 
off the shelf for the GPS frequencies that are inexpensive.


You don't need insane sampling rates. Think in terms of subharmonic 
sampling.





Heh..That's pretty much the design i thought of, though using a higher
sampling frequency (100 to 200Msps) which would allow to coherently
decode the E5a and E5b signals together. There is an ADC from National
that can do 200Msps for 20 bucks, with FPGA friendly parallel output
(ADC08200).


Is there a publically-available antenna design that's easy to
fabricate, has a stable phase center, covers 1100--1600 MHz, and has a
good pattern over this band with low cross-polarization?  Even a large
choke-ring design would be okay if it's fully specified.


I think there are some crossed dipole designs around.  What about quad 
helix?



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Re: [time-nuts] GPS receiver vs local oscillator

[Jim Lux]

On 2/2/12 1:49 AM, Hal Murray wrote:


If I want to decode a GPS signal, do I have to know (or figure out) the
frequency of the local oscillator?  Or does it drop out of the calculations,
somehow?




Yes, it comes out in the calculations.

That's why you need 4 satellites.  You solve for x,y,z and local clock 
offset. (and, in reality you also have to solve for xdot,ydot,zdot, and 
fdot)


If you have a stationary receiver, or a known position, then you have an 
additional constraint or two you can fold into the solution, so you 
don't need as many observables.


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Re: [time-nuts] GPS SDR

[Jim Lux]

On 2/2/12 1:28 AM, Attila Kinali wrote:

On Wed, 01 Feb 2012 21:53:16 -0800
Jim Lux  wrote:


You don't need the ADC: you just need a limiter/comparator.


Yes, but this degrades sensitivity quite a lot.


You don't need insane sampling rates. Think in terms of subharmonic
sampling.


This requires that you have an ADC that has the anlog bandwidth of
the signal. And ADCs with a analog BW in the GHz range are damn expensive
and hard to get.

Also a problem is to get the sampling frequency right if you want to
sample more than one band. Downmixing solves both of these problems
at the cost of higher complexity and a bit more noise.


Yes, if you need lots o'bits, but a single bit sampler with wide 
bandwidth is easy (which is why they do it).  It's basically a D-latch 
at the end of the amplifier/limiter chain.


There is a sampling rate around 38-39 MHz that works out nicely for all 
three bands (actually, any rate in that range probably works..I haven't 
looked).. It helps that the 3 GPS frequencies are related to a common 
base.  A few minutes work with an Excel spreadsheet trying frequencies 
will probably find something that works: You want the carrier to alias 
to about a quarter of the sample rate (so the entire signal is in the 
sample bandwidth without aliasing), but not exactly in the center 
(because having some known frequency offset means your Doppler tracking 
doesn't have to go through zero)


40MHz gives you a sample bandwidth of 20 MHz, so you could probably 
sample slower, but I think having more samples/chip makes the tracking 
easier (if nothing else, oversampling is like having more bits in your ADC)





Is there a publically-available antenna design that's easy to
fabricate, has a stable phase center, covers 1100--1600 MHz, and has a
good pattern over this band with low cross-polarization?  Even a large
choke-ring design would be okay if it's fully specified.


I think there are some crossed dipole designs around.  What about quad
helix?


Crossed dipole are narrow band and not easy to build as dual band designs
at least at those frequencies. Quad helix needs quite a precision to get
the right frequency and dual band designs (stacked helixes) get even more
difficult.


I suspect that you're right.. the actual antenna may be simple, the 
design is hard.  The antennas we use for multiband look like a crossed 
dipole on the surface of a hemisphere, but the actual elements are a 
very odd shape: generally a wide strip, but there are some lumps and 
bumps in the outline.


I'm going to guess that they were designed with some FEM code, and then 
iterated by hand.  If you knew the shapes, it would be pretty easy to 
build, though: copper foil tape on an appropriate substrate.  As you 
note, precision is important.


I'd go hunting through patents assigned to Dorne & Margolin. (part of 
EDO, these days, I think).  Or even maybe looking at their datasheets.


There's also what they call the "helibowl" antenna which is some form of 
helix in a bowl shaped reflector/ground plane. googling that might turn 
up something.




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Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)

[Jim Lux]

On 2/2/12 12:05 PM, Daniel Schultz wrote:

I found this homebrew GPS receiver project recently:

http://www.holmea.demon.co.uk/GPS/Main.htm

No custom specialized chips that are unavailable in small quantities, or which
will go obsolete in a few months. I think the best solution for the open
source GPS community is to design open source receivers with commodity parts
that won't be discontinued in the near future, or for which another commodity
part can be substituted if need be. Maybe somebody can extend this design with
a 2-bit ADC on the end (not me, too many projects here already...)

Dan Schultz N8FGV



I still think that finding appropriate off the shelf parts to make a 
subharmonic sampler would be a better strategy..


It's all about whether you want IF filters and a mixer+LO or RF filters. 
 I think the amps are the same either way.



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Re: [time-nuts] GPS SDR

[Jim Lux]

On 2/2/12 9:39 AM, Attila Kinali wrote:

On Thu, 02 Feb 2012 07:49:53 -0800
Jim Lux  wrote:

[

There is a sampling rate around 38-39 MHz that works out nicely for all
three bands (actually, any rate in that range probably works..I haven't
looked).. It helps that the 3 GPS frequencies are related to a common
base.


Only if you sample them seperately. Which requires seperate, sharp
filters for all of them. Also something that isn't that easy to do.


The filters don't have to be all that sharp.  What you typically do is a 
chain of amp/filter/amp/filter/amp/filter, etc, for about 6 stages.


I'll ask around about the filters, but I suspect they're a pretty 
standard ceramic thing (it's a bit high frequency to be a SAW), and 
since GPS frequencies are "standard" it's likely to be a "catalog part".




Also do not forget that Galileo E1 signals have about a 20MHz Bandwidth.
The combined E5 frequencies have about 50MHz. I think i've read somewhere
that you can get away with 8MHz for the E1 signal. Don't know how
the E5 behaves if you limit its bandwith.


yes, that might be tricky



[Antennas]

That's why i said that probably a patch antenna build out of PCBs
is the best solution. You can get the copper sheet at 0.1mm precision
which would define frequency and polarity properties quite well.
The only thing that would have to be done by hand would be the distance
from the ground plate. I guestimate that this value is not as critical
and that 0.5mm variation should be ok.


I've seen dual band patches that were pretty simple. One was air 
dielectric, so the interplate spacing was set mostly by the spacers.






I'd go hunting through patents assigned to Dorne&  Margolin. (part of
EDO, these days, I think).  Or even maybe looking at their datasheets.

There's also what they call the "helibowl" antenna which is some form of
helix in a bowl shaped reflector/ground plane. googling that might turn
up something.



From my understanding of antenna theory (which is very little),

these are mostly variations on the directivity characteristic
(ie to get a more favorable distribution), but do not change
much the frequency characteristics. Ie if you don't have the
frequency characteristics right with a straight design, there
wont be much chance to get them right with a "shaped" design.



True in some designs.. however, in general "fat" elements have wider 
bandwidth.  Adding oddball protrusions and notches can flatten out a 
response quite nicely.


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Re: [time-nuts] Why a 10MHz sinewave output?

[Jim Lux]

On 2/6/12 6:14 AM, paul swed wrote:

Indeed the long cable runs are tough. Though today we have differential
cable drivers that do quite well to the Ghz range. But certainly back in
the dark ages the sine wave was a very reasonable way to go.
Regards
Paul

we may have GHz bandwidth drivers, but that doesn't solve the issue of 
frequency dependent propagation through a cable.  At lowish frequencies 
(<100 MHz) I'd suspect that the difference is more one of amplitude than 
phase, but still, it's something that has to be dealt with.


One could just have a narrow band filter at the receiving end to pick up 
only the fundamental, but then, why not just send only the fundamental.


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Re: [time-nuts] Why a 10MHz sinewave output?

[Jim Lux]

On 2/6/12 6:47 AM, paul swed wrote:

Well right you are thats why todays chips have equalizers and such.
But then its all getting crazy complicated even though its in a itty bitty
chip.
My distribution is made of high quality television analog amps and I have
in general made amplifiers and such with parts I can still easily pickup
and solder to.
But still I always do wonder about tinkering with a square wave dist
system. Though I doubt I will ever actually do anything.
KISS is the general principal.
Regards
Paul.




"adaptive equalizer" and "precision frequency/time distribution" are 
going to be very uneasy bedfellows..


Of course, if you're just looking for distribution of house black burst 
or analog video, that's probably ok.  You're looking for good waveform 
fidelity, rather than precise knowledge of time delays.


In most of the precision measurement systems I fool with we look for 
parts in 1E10 or better.  Say, 1 degree of phase at 32 GHz.. if you're 
multiplying up from a 10 MHz reference for that, the x3200 
multiplication means you need to be pretty savvy about how your 
references are distributed (and, as well, how a phase change in the 
harmonic content might screw up the zero crossings)


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Re: [time-nuts] Why a 10MHz sinewave output?

[Jim Lux]

On 2/6/12 7:41 AM, paul swed wrote:

Jim
I want to be careful this is not my thread.
the question came up.
Why sine wave.
Though I do appreciate your comments.
Regards



I think it boils down to "it's easier to get high precision when you 
only have one frequency to worry about"




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Re: [time-nuts] Why a 10MHz sinewave output

[Jim Lux]

On 2/7/12 1:30 PM, Attila Kinali wrote:

On Tue, 07 Feb 2012 16:15:44 -0500
Mike Naruta AA8K  wrote:


On 02/07/2012 03:59 PM, Attila Kinali wrote:

while TV and radio uses 75R. (there was once a reason
for this, but i don't know it).


A 4:1 balun takes old 300 ohm twinlead to 75 ohms.


Thanks! This explains half it :-)
Do you know why a 4:1 balun was used?


A dipole has a feed point impedance of about 65-75 ohms.  A folded 
dipole has an impedance of 4 times that, so 300 ohm twinlead was a nice 
match.


75ohms is, in general, the lowest loss impedance for a given dielectric 
(based on the ratio of inner and outer diameters and skin depth, etc.)


  30 some odd ohms is the highest power handling impedance (lowest peak 
E-field)




And do you know why other RF stuff and lab equipment is 50R?


Compromise of one sort or another.

http://www.microwaves101.com has a nice discussion of this..


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Re: [time-nuts] Using digital broadcast TV for timing?

[Jim Lux]

On 2/7/12 6:01 PM, Chris Albertson wrote:

GPS requires a good view of the sky,  Hard to do in say the 7th floor
of a 40 story building if you have no windows.   I'm wondering about
using the new digital TV signals for timing.

I'm pretty sure there is time code in the signal and I'm pretty sure
the bits are clocked at a very accurate rate.   Also TV receivers are
very easy to find and put "hooks" into.  I'd bet the broadcast TV
signal could be almost as good as GPS.


Actually, no... because it's so easy to do frame buffering/time base 
correcting to fix anything.


Back in the bad old days of analog everything, you needed really good 
sync and timing to make things like switchers and faders work. A time 
base corrector was wretchedly expensive, so you'd go to a lot of work 
distributing black burst around and syncing your tape machines, etc.





The plan is to try and phase lock a local oscillator and use a very
long time constant on the loop filter.   I bet the TV transmitters are
locked to GPS and over a long enough time are as good as GPS.  Also in
many cities there are many TV transmitters, should be able to take
advantage of that.

  Before I try some experiments anyone want to tell me why I'm wrong?



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Re: [time-nuts] PTS synthesizers

[Jim Lux]

On 2/8/12 3:23 PM, EB4APL wrote:

I want to take advantage of the topic just to ask if anybody has any
manual or schematics of the PTS 040. I realize that the PTS 160 is close
enough, taking in account the different frequency range, and they use
almost the same modules but it would be nice to have the right manual.

What is about the remote interface? Please, share the info.



Way back in the 80s, I used a PTS and the remote interface, so I'm going 
off memory. As I recall, it's basically a BCD parallel thing with a 
strobe. The general architecture of their synthesizers is a series of 
decade modules, so the parallel interface just extends that to as many 
digits as you have modules.


Settling time to the new frequency is pretty fast (<1 microsecond, I 
think) but not necessarily phase continuous, and, there can be glitches 
during the transition (i.e. if one module switches faster than the 
others).  no fancy-shmancy DDSes back in those days.


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Re: [time-nuts] Why a 10MHz sinewave output?

[Jim Lux]

On 2/8/12 4:51 PM, Magnus Danielson wrote:

On 02/08/2012 03:25 PM, Craig S McCartney wrote:

We already have one of those that everybody can use. It's called the
earth.


Yes, but you don't have it hanging in a neat position in your office,
living room or lab, now do you? Besides, if you are a time-nut your rock
will be more time-accurate than the real thing. :)

I haven't special ordered a backup earth for my lab, or at least I won't
admit to it, as you all know that I have at least three operational and
a few stand-bys to put into operation in case I need to service one of
them.



And now you know why we keep sending those spacecraft with high 
performance radios to Mars.  Because, you know, with all those 
earthquakes and tsunamis, the Earth rotation keeps changing. And that 
enormously massive moon also interacts with the rotation too, not to 
mention our thick atmosphere.


Mars, tiny moons, almost no atmosphere, no oceans, seismically quiet...

I'll pitch it as a new slogan: "Mars clocks, when Earth rotation just 
isn't stable enough."


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Re: [time-nuts] PTS synthesizers

[Jim Lux]

On 2/8/12 4:47 PM, EB4APL wrote:

Jim,

I already have the info on the remote interface, taken from the PTS 160
doc and other sources, I was asking if he was talking about some
specific gadget.

I also was using at those years some remotely controlled PTS's , did you
know the JPL MK IV receiver exciter? I think it was also a 040 but I'm
not sure, because these changed the phase smoothly but I think that
there is an option with a DDS to allow such thing.
Unfortunatelly those exciters are now dismantled and I think the doc was
dumped, anyway I'll have to make a phone call.




Could be.  We have tons and tons of 3325Bs and 3325As floating around, 
though. I haven't seen any PTS recently, however, a quick check of the 
asset database shows a fair number of them "owned" by Rabi Wang and 
William Diener. The latter has most of them.. Models PTS040SANIX-7, 
PTS250 and X10SAN10 for the most part.
Both of those guys are in the Frequency and Timing Advanced Instrument 
Development Group.




A couple years ago, we cleaned out some storage closets FULL of those 
gold plated brick shaped modules that made up the Mark III (at least 
that's what I was told).


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[time-nuts] science projects

[Jim Lux]

 While delayed, I would think that the signal freqs would still need to 
be maintained...  hmmm, maybe not...   interesting science project... 
anyone?  anyone?  ;-)


Jerry




I'm waiting to see a good time-nuts project at the science fair. (at any 
level up to ISEF)


There's a lot of good ones out there (perhaps not on the scale of tvb's 
experimental demonstration of gravitational effects on atomic clocks) 
that would lend themselves to execution by everyone from 6th to 12th 
grade.  Clearly, since people do spend their entire professional life 
doing this and write dissertations on it, it can be up to ISEF or 
Siemens Talent Search standards.


Maybe we could come up with a suggested list and start shopping it around.

Jim

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Re: [time-nuts] science projects

[Jim Lux]

On 2/8/12 6:03 PM, Chris Albertson wrote:

The number one TN science fair project would have to be measuring the
speed of light using some simple, inexpensive method such as
reflecting sunlight from rotating mirrors


Actually, that's probably not a good project: it's been done, in almost 
exactly that way.
The key to a winning project is doing something that nobody's done 
before.  It doesn't mean it has to be Nobel unique, but just different.


For instance, if you came up with an unusual way to measure speed of 
light (other than all the classic spinning mirror, toothed wheel, 
interferometer schemes)


Or, if you were to measure the Allen Deviation of a bunch of pendulums 
of different types. This would be a good junior division (grade 6,7,8: 
age 11-13) project because it would allow you to do some statistics 
(very unusual in junior division, beyond the usual misapplication of 
Excel Data Analysis tools), and if you could come up with some theory 
about why the ADEV would vary with material or length (e.g. smaller 
effect of air drag or something), you could test it.


In senior division, to be a top project, it would have to be something 
like we discuss on this list.  tvb's Cs clock verification of Einstein 
might work, but you'd have to be pretty good at showing why it's not 
just a rehash of someone else's traveling clock demo.  Something with 
coupled oscillator behavior in an interesting context would be 
interesting. (measuring the small coupling between mechanical 
oscillators on a concrete floor as a function of distance or orientation)


Building your own atomic standard from scratch would be impressive, but 
would be unlikely to be a top winner at state or ISEF level (they tend 
not to reward "design and build" engineering projects, even in the 
engineering categories, unless you've got some novel design feature 
you're trying.)


Characterizing some sort of oscillators could be a winner, especially if 
it's a kind of oscillator with usefulness that hasn't been well 
characterized before.





On Wed, Feb 8, 2012 at 5:44 PM, Jim Lux  wrote:

  While delayed, I would think that the signal freqs would still need to be
maintained...  hmmm, maybe not...   interesting science project... anyone?
  anyone?  ;-)

Jerry




I'm waiting to see a good time-nuts project at the science fair. (at any
level up to ISEF)



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Re: [time-nuts] science projects

[Jim Lux]

s not too hard to get hooked up with 
someone with good lab facilities, but the field is moving so fast that 
you run the risk of doing what labs pay a technician $15/hr to do.  The 
student gets so caught up in the miracle of doing PCR and sequencing and 
stuff that they don't wind up doing any real science.






This year, I'm working on making a monolithic CMOS THz imaging array with
built-in signal processing integrated circuit.  (Just in case you're
wondering, my I'm employeed at the TxACE center at UTD as a intern).  My
job is to basically design on the transistor level and integrate the signal
processing circuit into the CMOS THz imaging array.  At the end, I plan to
use this project and compete in STS, Siemens, and ISEF.  Unlike my last
year's project, monolithic THz imaging arrays with on-chip signal
processing is something relatively new.


I assume you've seen the new IEEE transactions on THz stuff edited by 
Peter Siegel?  If you haven't, you can be sure some of the judges have. 
(although I won't be judging your project if I recognize it)  Be careful 
about the "it has to be all your project to win" thing.




Why is a teenager (me) doing on this list?  Because I have a passion for
electronics, especially analog and RF ever since when I was very young.  I
love what I'm doing and I dont plan on stopping.

Ok I'll stop rambling now...sorry for the long email guys...

Ray Xu
KF5LJO

On Wed, Feb 8, 2012 at 8:03 PM, Chris Albertson
wrote:


The number one TN science fair project would have to be measuring the
speed of light using some simple, inexpensive method such as
reflecting sunlight from rotating mirrors

On Wed, Feb 8, 2012 at 5:44 PM, Jim Lux  wrote:

  While delayed, I would think that the signal freqs would still need to

be

maintained...  hmmm, maybe not...   interesting science project...

anyone?

  anyone?  ;-)

Jerry




I'm waiting to see a good time-nuts project at the science fair. (at any
level up to ISEF)

There's a lot of good ones out there (perhaps not on the scale of tvb's
experimental demonstration of gravitational effects on atomic clocks)

that

would lend themselves to execution by everyone from 6th to 12th grade.
  Clearly, since people do spend their entire professional life doing this
and write dissertations on it, it can be up to ISEF or Siemens Talent

Search

standards.

Maybe we could come up with a suggested list and start shopping it

around.


Jim

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--

Chris Albertson
Redondo Beach, California

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[time-nuts] earth as a clock

[Jim Lux]

On 2/8/12 8:11 PM, Ed Palmer wrote:
> I thought the same thing but I think Mark was referring to the end date
> of the Mayan calender. Now those guys were Time-Nuts!!
>
But oddly, as Feynman pointed out, they only used Venus, and not Mars 
(or Jupiter, although the synodic period is pretty long for Jupiter)..


Mars is pretty prominent in the morning sky these days, as it always is 
when a spacecraft is about a third of the way there, which is why I was 
reminded of it.


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Re: [time-nuts] Low-Cost Rubidium Performance

[Jim Lux]

On 2/9/12 4:51 AM, WarrenS wrote:

Indeed,
ADEV is for random freq variation not easily measured by other means.
Temperature fluctuations do not cause random freq changes and the
temperature's effect should be removed if one wants accurate long term
ADEV numbers.
Even daily diurnal cycles due to temperature can have major negative
effect on ADEV numbers as low as 2000 to 3000 seconds,
and if there is an Heater or AC cycling, then any ADEV numbers about a
few hundred seconds can be due to TempCoeff, which should not be
measured with ADEV or included in ADEV plots.
This is much the same as a single outlier data point that can screw up
the whole ADEV plot and make it pretty much meaningless and unrepeatable.
Ditto for linear ageing, Should be remove first if one wants true ADEV
plots.




Interesting point you make here.  The rising ADEV at 100-1000 second-ish 
tau in a system that should be better is a classic sign (at least around 
here) that temperature effects are showing up.


However, how could one remove that effect from the raw data?  And isn't 
the measurement of the "system", which includes the environmental effects.


I suppose you could run your widget in a temperature controlled chamber, 
get those numbers.  Then run it in a less controlled benchtop 
environment, and get those numbers, and claim that the difference is 
environmental.


But at some point, what you're interested is the performance of the 
system in the environment in which it will be used.  If you need good 
ADEV performance at the 1000 second tau, then you need an oven, a vacuum 
bottle, or a better design that's less environment sensitive.


 (difference between TRL6 and lower, for those into such things)

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Re: [time-nuts] Low-Cost Rubidium Performance

[Jim Lux]

On 2/9/12 8:42 AM, Magnus Danielson wrote:

On 02/09/2012 04:10 PM, Jim Lux wrote:




Interesting point you make here. The rising ADEV at 100-1000 second-ish
tau in a system that should be better is a classic sign (at least around
here) that temperature effects are showing up.


I regularly see the building AC at 900-1000 s for instance.


However, how could one remove that effect from the raw data? And isn't
the measurement of the "system", which includes the environmental
effects.


ADEV and friends is there to handle random sources, where as this is a
systematic source.


But I would contend that unless you can externally measure that 
disturbance and remove it, it's a fundamental part of the frequency 
variation.  Since you don't have control over it, or necessarily have 
accurate information about it, it's not something that could be 
"calibrated out".


Say, for instance, I had an oscillator that was mounted in such a way 
that it rotated slowly once every hour. There would be a periodic 
variation in frequency, which could be accurately modeled and removed, 
so that wouldn't necessarily count in ADEV.


But temperature is random (although band limited), and so, for 
measurements over the 1000 second time scale, it's impossible to tell if 
the change was due to temperature or due to the underlying oscillator.







I suppose you could run your widget in a temperature controlled chamber,
get those numbers. Then run it in a less controlled benchtop
environment, and get those numbers, and claim that the difference is
environmental.

But at some point, what you're interested is the performance of the
system in the environment in which it will be used. If you need good
ADEV performance at the 1000 second tau, then you need an oven, a vacuum
bottle, or a better design that's less environment sensitive.


You could also build active systematic effect predictors to lower this
systematic effect.


Yes.  That's basically no different than controlling the environment. 
If the transfer function of environment to output is well known, and you 
know the environment, you could legitimately "remove" it from the 
measured output.





By doing proper logging of key environmental effects, build a model for
how the dominant variations will systematically affect the signal and
then remove that from the measurements you get a better random jitter
measurement.


Ah, but there's the rub.  Can you actually do that with acceptable 
performance?


I know that you can measure the temperature of a crystal and fairly 
accurately calibrate out the frequency change due to temperature (to the 
point where frequency can be used to measure temperature).  So now, your 
ADEV on the "calibrated" output would depend on the temperature 
measurement accuracy.  Essentially what you have done is reduced the 
tempco of the system.




Frequency drift of an oscillator is one such systematic effect. If it
where linear, processing it with ADEV would cause a sqrt(2) scale error.
Also, it would not give you a good prediction since usually you follow a
A*ln(B*t+1) curve which isn't matching the requirement, so you will only
get first degree compensation of that with HDEV style measures.


Yes, and I think that for variations that are easily and *accurately* 
modeled this is appropriate, however, your next sentence says it all.


Temperature variations is tricky to say the least.

When you have random and systematic effects, separate them and estimate
them separately and then build a combined prediction from these models.

Random jitter and deterministic jitter are two such aspects. Same
applies at longer taus as well.


Cheers,
Magnus

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Re: [time-nuts] science projects

[Jim Lux]

On 2/9/12 8:23 AM, Chris Albertson wrote:

I think it's odd that all these "science" projects are NOT doing any
science.   They sound like engineering to me.

So you build a neat mouse trap?  That is not science unless you have a
theory about mouse behavior and your trap is intended to test the
theory.Around here we do have these projects but we call them
"engineering" and they are judged by engineers.



It's the "international science and engineering fair", so both kinds 
show up.


The line between applied science and engineering is pretty fuzzy.

Is a verification of theoretical coupling between pendulums a science 
question or engineering question?  What about developing a better model 
to remove tidal effects on the pendulum? A lot of modern science is 
coming up with ever more precise and descriptive models, particularly if 
the model is not purely phenomenological, but is based on the underlying 
physics.




But even for engineering, there has to be significant "scientific 
method" applied.  Research in the field to understand the state of the 
art.  Formulation of a design/plan, and the expected performance of the 
device (aka "the hypothesis"), quantitative tests, etc.



Distinguish between "craftsmanship" and "engineering".. Even in the 
engineering categories, a mouse trap wouldn't necessarily do very well 
unless it there was something novel about it AND there were decent 
predictions of performance ahead of time that could be tested by the 
thing that gets built.


Lots of "I built a robot" kinds of projects that don't do well, even if 
well constructed.  "I built a robot that climbs trees using a technique 
nobody has ever used before" would do better.  "I built a robot that 
climbs trees using a method that improves on how monkeys climb trees" 
might do even better, depending.



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Re: [time-nuts] science projects

[Jim Lux]

Yes, a fun project, and a fine physics lab exercise.  But not a good 
science fair project because it doesn't meet the "originality" bar.


This is something that I confess I had a hard time figuring out what 
that meant when I was entering science fairs... as it happened, my 
projects *were* original (reviewed in retrospect), but I couldn't figure 
out how you'd evaluate it at the time.


In general, if the general idea for a project came from a published list 
or book, that would be ok. But if the method of attacking the problem 
also came from a book or the web, that wouldn't.


So a good topic to prompt projects would be "Measure the speed of light 
in a novel way".


If you were to do Roemer's technique from the 17th century, but do it in 
a clever way (webcams, telescopes, etc.) I think that would do ok in the 
junior division at least.  (i.e. removing the human measurement element 
is a good experimental refinement on the basic technique).


Or if you were to use some other extra terrestrial event as the 
predictable time hack at a varying distance.


Here's a wild one.. Set up  detectors some distance apart where an 
Iridium Flash will be visible (http://www.heavens-above.com/)  The flash 
comes from the satellite, and the path length to the two detectors will 
be different, so you will see the pulse at a different time.  By knowing 
the distance between the detectors and the angular displacement of the 
image with reference to something, you could figure out the distance to 
the satellite, and therefore, the difference in propagation distance 
between satellite and each sensor.



But these wouldn't hack it in Senior division.


On 2/9/12 7:19 AM, Brooke Clarke wrote:

Hi Jim:

Check out:
http://www.ted.com/talks/lang/eng/clifford_stoll_on_everything.html

Here's part of an email from Clifford:
"Oh, the speed of light?

For detectors, I use two fast-response photodiodes and feed their
outputs into opamps.

The experiment uses one cheap laserpointer (they cost a buck or two on
ebay - I buy 25 at once, and then select the ones with the fastest
switching rate.)

The laser pointer is fed by a signal generator (I use an HP 3312A); the
square wave output connects to the laser pointer with a pair of
clipleads. I start with the laser switching about once a second, to show
the kids that it really is turning on and off. THen I boost the speed to
a few hertz, then tens, and hundreds of hertz. Eventually, I get it
switching on/off at 2 to 5 MHz.

I aim this switched laser beam at a distant mirror (across the room -
maybe 10 or 15 meters away). Coming back along almost the same path,
this long-path beam then hits a lens which focuses the beam onto one
photodiode. The photodiode feeds its pulses into an opamp, and then into
the bottom trace of a dual trace 100MHz oscilloscope.

I then create a short-path beam using a beamsplitter that's right next
to the laserpointer. I use a piece of microscope slide cover-slide for
the beamsplitter. A few inches from the beamsplitter I set the
short-path photodiode, which goes through the 2nd opamp and into the
upper beam of the squigglescope.

There'll be a time delay in the arrival of the long-path beam; I get the
students to measure this time difference. Then we measure the path
lenght difference with a tape measure, do a division, and out pops the
local speed of light.

Lots of gotcha's ... for instance, I make sure that I trigger the
oscilloscope on the output of the function generator. Also, alignment is
very difficult, and requires rock-solid furniture (seldom found in
classrooms).

It's a fun project with high school students, because we spend a long
time afterwards discussing errors and problems in the system ...
typically, we measure things about 20 or 30 percent off. The main source
of error turns out to be mismatched responses in the two photodiode/opamps.



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Re: [time-nuts] science projects

[Jim Lux]

On 2/9/12 4:00 PM, Bill Hawkins wrote:

Fellow time scientists,

Here's my view of the difference between science and engineering:



If marketing studies show a positive return on investment, engineers
are turned loose to solve the problems revealed as the details of
building or manufacturing the new thing are studied.



I'd differ here.  My contention is that (creative) engineers are 
fundamentally lazy.. they want to reduce the effort to accomplish 
something.  Imagine people who have been wading across a river for 
centuries.. an engineer says, "there must be a better way", and invents 
a bridge.


Although that's really invention.
Engineering is also the effective use of knowledge to predict future 
behavior.  A craftsman might use a particular size piece of stone or 
steel because that's tradition, or because they have a "feel" for it. An 
engineer would use it because they can calculate the loads, they know 
the material properties, so they are making the choice based on 
quantitative models and theory.


However, engineers tend to be focused more on the end result or process: 
the how, rather than the why.  They're interested in why, but often 
that's because that lets them do a better how.


Scientists tend to be focused on understanding the why.

But, as mentioned, when you get to applied science.. Is the guy 
measuring fission cross sections in a critical assembly doing basic 
physics to understand chain reactions or is he building a bomb or 
reactor, for which he needs to understand chain reactions?


There's a reputational thing too.. Scientists are, in some ways, 
considered higher class than engineers.  I think this is a holdover from 
18th and 19th class distinction: gentleman scientist vs tradesman 
engineer.  An awful lot of what Lord Rayleigh did was engineering, 
although I'll bet that most biographies describe him as a scientist.


The whole, "if it has practical value, it's trade", thing:  like amateur 
sports being somehow "better" than doing it for money.



There is a notable distinction here at work (NASA/JPL) in scientists vs 
engineers, but it's not so much about background or motivations, but in 
time scale of concern.


Consider a scientist for a space probe to investigate something: Mars. 
They've got these questions about Mars that they've had for years, and 
they've worked for years and years to get a mission funded, to get the 
data they need to answer their question, and they expect to spend the 
rest of their life working on that data.


The engineers designing and building and operating that probe, on the 
other hand, came to the party fairly late.  They were working on some 
other spacecraft perhaps, but now they're designing and building the 
instruments or infrastructure to make the measurement.  They get it 
built, launch it, and then, they're off to make the next space probe or 
instrument.  Not that they aren't interested in what they built, or the 
data it will return, but nobody is willing to pay them to do that. (and, 
in a utilitarian sense, that's not an effective use of their hard won 
and unique skill set).


The other distinction is the amount of personal investment in the whole 
thing.  Typically, the probe is NOT the engineer's life work. If it 
blows up on the launch pad, they'll be disappointed, but life goes on. 
For the scientist, though, this is a catastrophic life disaster.  The 
culmination of their every hope and dream for the past decades has just 
vanished in a ball of fire.


Of course, the distinction is not as hard as all that... plenty of 
engineers work for decades on a particular instrument or spacecraft and 
are pretty invested in it.  However, I still think that the reaction to 
the loss of the spacecraft is different:  the engineer regrets the loss 
of the invested time and knowledge, and perhaps the specialized 
knowledge for which there is no use now which was sort difficult to 
acquire.  But the scientist finds that the burning question which has 
motivated them for years will likely never be answered, or worse, from a 
personal pride standpoint, will be answered by someone else.


(I say all this as a Principal Investigator on a payload that will 
hopefully NOT disappear in a ball of fire in June)


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Re: [time-nuts] science projects

[Jim Lux]

On 2/10/12 1:37 AM, Hal Murray wrote:



It's the "international science and engineering fair", so both kinds  show
up.



The line between applied science and engineering is pretty fuzzy.


There is another category.  I'm not sure what the right term is.  How about
"just having fun"?



Most definitely..




I think it's neat to see an experiment or demo that is well done.  I expect a
kid will have fun and learn a lot setting one up.   With luck, some of both
the fun and learning will rub off on other kids.


yes, and that is something to be encouraged.  However, science fairs ARE 
competitive, so what you want is "original" and "fun".  Entrants who had 
fun working on their project ALWAYS place better than those slogging it 
out because they think it will burnish their college app or because it's 
an assignment.  (My worst performance in 6 years of competition was when 
the other ideas for that year didn't pan out, and I had to put something 
together in a hurry.)


The best entrants are the ones who are curious about everything, found 
something they wanted to investigate, know an amazing amount of obscure 
background information, and went about it in a competent way.


It's the classic "that's funny" or "I wish it would do X" thing.



I use demo to refer to an experiment that doesn't involve taking data.  You
just observe that if I do X, Y happens.  Or if I make X bigger, Y gets bigger.


Or qualitative vs quantitative.

this is a good distinction.  What wins (leaving aside the pedagogical 
value aspect) is quantitative.   "Are redheads taller than blondes?" can 
be done both ways. If the question is reformulated as "Are redheads 
*significantly* taller than blondes? and is my school different from the 
population at large?" you've got the beginnings of a good project.




I'm probably biased.  A friend works at the Exploratorium.  For those of you
who don't know about it, it's the great grandaddy of the hands-on science
museums.  They have hundreds of exhibits.  It's highly recommended if you
ever get to San Francisco.


Frank Oppenheimer had a real vision to get that going.  It's a wonderful 
place.





Paul teaches science to high-school science teachers.  A lot of that involves
showing them low cost experiments/demos.  The teachers are always finding
new/neat ways to do things.



Yes.. and that's ever more important.  My daughter's 8th grade physical 
sciences teacher was far better at imparting the fundamentals of 
chemistry than her 10th grade Chemistry teacher. That's something that 
comes with experience and enthusiasm and confidence, I think.


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Re: [time-nuts] science projects

[Jim Lux]

On 2/10/12 2:05 AM, Chris Dawes wrote:


Thanks Hal,

Will have to visit next time I am in San Fran sounds interesting



Makes a nice, but busy, day to do the Exploratorium and the California 
Academy of Sciences/Steinhart Aquarium.  They're pretty close to each 
other, so it's not like you have to drive across town.



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Re: [time-nuts] Literature on low noise and HF electronics

[Jim Lux]

On 2/11/12 12:43 AM, Attila Kinali wrote:

Moin,

The recent discussions have made it again clear to me, that i lack
a lot of knowledge in electronics. Especially when it comes to
the black arts: analog stuff, HF, getting the most ouf of a transistor,
or doing it really really low noise.

Could someone recomend anything to read that would get me more
insights and knowledge on these topics? May it be books, papers
or search terms for google.


Thanks in advance

Attila Kinali



RF circuit design, by Bowick
http://www.amazon.com/Circuit-Design-Second-Christopher-Bowick/dp/0750685182/ref=pd_sim_b_1

It's kind of a handbook of design with a fair amount of theory.  I don't 
know that it gets into esoterica of ultimate low noise.



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Re: [time-nuts] Literature on low noise and HF electronics

[Jim Lux]

On 2/11/12 8:00 PM, Said Jackson wrote:

The appnotes from LT especially Jim Williams articles. LT used to print these 
in book form.

Check out the V to F designs, and the data acquisition stuff. Very practical 
with real world components and test results. Very high end analog stuff.

Most textbooks are totally useless, the authors trying to hide their lack of 
real world experience with lots of math and theory. Also Bob Pease published 
some books through EDN quite good also.




indeed.. ap notes are your friend, esp on design.

There is so much "art" in low noise design

getting ultimate performance is all about the individual devices, and 
fiddling with it to find what works for it.


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Re: [time-nuts] Picotest U6200A & Timelab

[Jim Lux]

On 2/11/12 7:42 AM, paul swed wrote:

Indeed interesting but the 5370s seem to go for $300-400 and this $1750.
I had been lucky to get my 5370s pre-interest price accelerator so $50-75.
Because who would ever want such a heavy thing?
Much as I love the modern interfaces, size, quite, and low power
consumption. The boat anchors stay. ;-)



But comparing "new with warranty" to "used" isn't necessarily a fair 
comparison.  What you're essentially doing is trading your labor (to 
potentially make repairs) and risk for money, so the trade between the 
two is highly dependent on your risk acceptance posture and your labor 
costs.


It's also important if you need more than a "one-off" system.

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Re: [time-nuts] [FMT-nuts] LightSquared is Toast!!

[Jim Lux]

On 2/15/12 7:16 AM, Peter Vince wrote:

See:<
http://www.nytimes.com/2012/02/15/business/media/fcc-bars-airwave-use-for-broadband-plan.html?_r=1&scp=3&sq=lightsquared&st=cse




Err.. not necessarily.  As one of the commentators in the business press 
said yesterday (paraphrasing).. Harbinger needs to decide whether to 
shut down LightSquared and take their losses now, or arrange their funds 
for the legal battles to come.


When you have billions riding on the bet, a few million in legal fees 
(which is tens of thousands of billable hours: a LOT of work) to go to 
court to get the decision changed isn't always a big problem.


As quoted in the lore of Python.. "I'm not dead yet..."





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Re: [time-nuts] Fwd: FE-5680A Contact FEI

[Jim Lux]

On 2/17/12 5:27 AM, paul swed wrote:

The used market makes no difference to them. No revenue stream.
In fact I would say you are swatting at the behive. It would be wise to
leave them alone since several have reached out and already had a poor
experience.
As someone else pointed out this is what gets manufactures to demand
crushing or drilling holes etc. Further the very hard work being done by
this group to understand these units can be at risk if FEI decides to
really get cranky.
Regards
Paul
WB8TSL




A lot of companies don't provide docs on request because it costs 
significant money to do so, and provides little bottom line return. 
Someone has to dig in the files for the old drawings, which are almost 
certainly marked "proprietary" (on general principle).  Then, they have 
to through some sort of redaction/release process to make sure it's not 
dangerous, illegal, or unwise to release it.


None of which contributes much to their bottom line, and more 
particularly, none of this helps the engineer stuck with it get his or 
her deliverables done on schedule and on budget.


Net result is, unless you have a friend in the company who's willing to 
invest some time for free, it isn't going to happen, if it's not a 
standard policy.



As Paul pointed out, this is probably not perceived as a revenue stream.

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Re: [time-nuts] Fwd: FE-5680A Contact FEI

[Jim Lux]

On 2/17/12 7:02 AM, Bill Riches wrote:

Good points made - no income for the company, However on the other side of
the coin - look at Agilient having available all of the old HP manuals for
download even though there is no income to them.  I wonder if it was a
requirement of them to supply HP manuals when they absorbed HP.

I just purchased a new HP Pavilion laptop and was surprised to see that you
can download a service manual from HP with part numbers and it has
disassembly instructions - don't know of any other mfgs that do that.  Of
course HP computer company does not have any connection with the original HP
- or do they...



I think you will find that there's no particular rhyme or reason to 
documents being available. Contractual obligations are probably way down 
the list of reasons. More, it's just a "company habit" (I won't go so 
far as to say culture).


Aglient has such a huge installed base, and lots and lots of HP gear 
still being used. In their case, it probably saves them money to have it 
online, otherwise they'd have to have a whole department printing off 
copies, shipping them, etc.


Companies that make "components" or "assemblies" (e.g. Wenzel) and who 
do a lot of custom work are less likely.  Wenzel has all their catalog 
units online, but it would be impractical for them to just publish all 
the customs.. they'd have to do the export control review and 
proprietary review, and they're not a very big shop.  If you happened to 
ask when they weren't very busy, they'd probably be more helpful than 
when they've got a big order they're trying to get out.



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[time-nuts] export controls and reverse engineering

[Jim Lux]

"Do you believe there may be a problem for those who are 
reverse-engineering, and posting on the open net, items which may be 
covered under these regulations?


If you do, you may want to consider contacting them off-list and letting 
them know your concern.


Peter

"


Man, export controls are a complex, confusing, and not at all tidy and 
rule-driven so that mere engineers can figure out what is covered and 
what isn't.  It is left up to diplomats and folks at departments of 
Commerce and State (in the US, anyway) to figure out using whatever 
means they have at their disposal.  (When I started getting into the 
whole export control and negotiating licenses thing at work, the first 
thing they told me was that as an engineer, I'd find it horribly 
frustrating, because it doesn't necessarily make sense)



In general, I would think that reverse engineering something bought 
surplus would NOT be subject to export controls.  Obviously, if a 
spacecraft or spare nuclear weapon fell in your backyard and you 
commenced reversing it, that would probably raise some issues.


A lot revolves around whether the thing you are fooling with is 
considered a "defense article" or "munition", for which you need to go 
to the lists.  Spaceflight qualified atomic clocks are definitely on 
that list, but these are not them.  FEI does, however, produce things 
that are export controlled, so they may take the easy way and treat 
everything as controlled unless there's a reason not to: hence the 
boiler plate on invoices from parts distributors when you order BNC 
jacks warning you about export controls.



The US Munitions List (USML) does have a whole section on atomic 
frequency standards, and you want to take a look at the performances 
listed there and see if you're in the ballpark (I suspect not).  They 
would be interested in particularly small, low power, or rugged sources.



Be aware that ITAR is only half of export control.  Department of 
Commerce also has the EAR.  There you want to look at "dual-use" 
technologies.






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Re: [time-nuts] Update on Rb Performance

[Jim Lux]

On 2/19/12 2:47 PM, Tom Van Baak wrote:

There seems to be some confusion about stability and drift; about
ADEV and other tools. The tone of this thread is not heading in a
positive direction.

So instead I will offer to put together a short tutorial or series of
tutorials that focus on factual education and gracious explanation.



Most excellent..
I'm always looking for this kind of thing for new engineers at work..

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Re: [time-nuts] Low-long-term-drift clock for board level integration?

[Jim Lux]

On 2/20/12 8:34 AM, Achim Vollhardt wrote:

Hi Bill,
what about White Rabbit?

http://www.ohwr.org/projects/white-rabbit/wiki/Description

Successor of NTP.. PTP: precision time protocol.

It delivers Gigabit Ethernet and precise (<1nsec) timing over singlemode
fiber. You would have to connect all devices into a fiber network
instead of a copper based network and all switches in between would have
to be WR compatible.. but this could solve your problem.

Javier Serrano (one of the developers) is also on this list.. he might
add/correct me.



I think the OP needs something over a large geographical area, and I 
don't know that PTP/1588 would work through a routed "internet" kind of 
connection.


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Re: [time-nuts] How best to exchange Large files?

[Jim Lux]

On 2/20/12 9:52 AM, WarrenS wrote:


Recording high speed and/or long general purpose raw Osc data, the file can 
become very large.
I'm looking for a simple, fast and easy (and cheap) way to transfer large 
compressed data files of up to say a 100 MB between time-nuts.
I know there are all kinds places one can store large files that others can then have 
access to,  so I do not want to use the "OLD" way of breaking it up into many 
small pieces.
I do not need to do this very often, so I do not want to sign up for any long 
term thing or maintain a Friends or face book type thing,
I'm just looking for an easy, temporary way (say lasting up to a week each) to 
transfer a few big files that are too large to email.
Suggestions anyone?



very big meaning "megabytes".. 10s of MB? GB?

What about something like dropbox?

If the files are big enough, this is, of course, what bit-torrent was 
invented for.


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Re: [time-nuts] Low-long-term-drift clock for board level integration?

[Jim Lux]

On 2/20/12 10:31 AM, Bob Camp wrote:

Hi

Simple answer:

A rack mount cesium standard is as good as you can get. Figure on 15 ns per day of 
drift. That gets you to 15 us in 1000 days. You may or may not get one that drifts 
that little, a lot depends on  little details. For>  3 years, consider an 
ensemble of cesiums. At $50K each cost can go up pretty fast.

There is nothing out there that will do better stand alone for less money. 
Either you get a sky view or you change the budget

Bob





But he *does* have the ability to have an external network connection.. 
So the real question is whether one could come up with a better-than-NTP 
scheme to get the 100 (or 10) microseconds.


I suspect that with sufficiently controlled network paths (which might 
be doable in a widescale deployment) and a tweaking of the NTP stuff, 
you might be able to get it to work.


100 microseconds out of a day is 1E-10, which is actually a fairly 
liberal drift spec for an OCXO or even a TCXO. (which are things like 
ppb/day)


Maybe there's a particular time of day (or day of week) when network 
uncertainties are minimal, or can be bounded.  So what you really need 
is a onboard oscillator that is good at "carry over" between periodic 
calibration checks.



One question about the 100 microsecond spec.. is that a worst case at 
any instant, or is it an average spec over a day (so a consistent 
diurnal variation would cancel out)


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Re: [time-nuts] Low-long-term-drift clock for board levelintegration?

[Jim Lux]

On 2/21/12 10:47 AM, Attila Kinali wrote:

On Tue, 21 Feb 2012 10:05:04 -0800
Chris Albertson  wrote:


Perhaps he has now given up on that approach and has
gone to using relative time and round trip timing which would work
even using a $2   TTL "can oscillator"


If you read carefully what the OP wrote, you'll see that he
wants to measure one way trips.

RTT is easy and well understood. You can use a standard PC and
get to ~100us resolution with no special components. If you take
a NIC with time stamping, you get well below that.

But the problem is, in order to understand how networks behave
exactly and how this behaviour is changing over time, you need
to know the one way delays (mostly due to asymetric routing
which leads to asymetric load etc pp). And to do this, you need
a global time scale for time stamping. There is no way around it.



What if one sends a message one way that triggers say, 10 response 
messages 1 second apart.   Then you get distribution statistics on the 
return path.  You still don't know what the absolute forward or reverse 
path time was, of course.



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Re: [time-nuts] Article in Metro (free London newspaper) about jamming GPS

[Jim Lux]

On 2/22/12 4:38 PM, Dr. David Kirkby wrote:

On the train this morning I picked up a copy of the Metro (there are
usually numerous copies on any train, as its free and does not take long
to read).

There was an article about financial institutions being concerned about
the time of their clocks being purposely altered by GPS manipulation so
someone can gain a trading advantage. I guess if you can make London a
bit slow, then you can determine if stocks have risen/fallen on other
markets and chose to buy or sell based on that fact. I guess you would
need a few seconds if the decisions were made by humans, but perhaps
microseconds would be enough if the decisions were made by computer.

I can't seem to find a copy of the article online.

Funny thing is there was a fictional TV program a week or so ago where
criminals claimed to be delaying supposedly real-time data to gain an
advantage. But in fact they were not in the plot - they just told other
criminals this story.



"The Sting"  Robert Redford and Paul Newman... a fine example of how a 
bit of time alteration/data delay can work.









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Re: [time-nuts] Neutrinos not so fast? (defectove connector)

[Jim Lux]

On 2/22/12 2:26 PM, Poul-Henning Kamp wrote:

In message<9a458dba-3875-43b2-8383-5ca2f86be...@leapsecond.com>, "Tom Van Baak
  (lab)" writes:


Could be on the electrical side of the adapter, not the optical
side. It's not impossible to get 60 ns of phase or trigger error
with RF connectors.


I don't buy that explanation.

It's very hard to get 60 ns *consistent* phase or trigger error,
with any kind of connector, almost no matter how you go about it.



A 10 meter cable with a good reflection/air gap where it should be flush 
butt joint?



20m of extra fiber sounds *much* more plausible.


Oops, I thought it was cable number A321241Z, not cable number A321242Z.



Inventing an excuse about a loose connector to cover up the mistake
sounds even more plausible.

You really don't want to defend your phd dissertation, being known
as the idiot who made a fool of both CERN and SanGrasso in one go.


Lends new meaning to the term "defense", I should think.







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Re: [time-nuts] Neutrinos not so fast? (defectove connector)

[Jim Lux]

On 2/23/12 6:24 AM, Alberto di Bene wrote:

On 2/23/2012 1:04 AM, Poul-Henning Kamp wrote:

I simply don't buy the story that tightening the connector makes
a consistent 60 nanoseconds difference on a signal.

I spoke with a physicist of Cern, friend of the leader of the team that
performed the Opera experiment.
He told me that the badly seated connector caused the amplitude of the
signal to be lower, and for this reason the trigger point, which was
set at a specific level, was reached 60ns later.
73  Alberto  I2PHD




Darn those finite rise times
I've been bitten more than once by this very phenomenon (which I admit 
doesn't say a lot for me.. being bitten once is ok, but since I've had 
multiple bites...)


But this brings up an interesting time-nut problem for the hive mind..

If you had to design some scheme for interconnecting "boxes" and wanted 
to transmit an accurate time sync, what should it look like, so that 
you're insensitive to things like rise time.


(maybe this harkens back to the discussion about 10 MHz, why sine vs 
square wave distribution)


It has to be a single signal (maybe a differential pair), because 
otherwise, don't you have potential for skew between the multiple signals.


Zerocrossing sort of works, if you take only one direction, but does 
asymmetry of the waveform screw you up?  (e.g. what's "zero".. is it 
half way between peak values + and -?)


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Re: [time-nuts] OT - Portable Digital 'scope

[Jim Lux]

On 2/23/12 1:25 PM, Robert LaJeunesse wrote:

FWIW Rigol pushes their 40MHz Analog Devices part to 100 MHz without any problem
(seen in eevblog teardown). Yes it's sort of cheating, but if the part works
fine because all of the suppliers parts now yeild that fast due to an improved
process well, it saves a few dollars / quid / drachma...

And the 40MSPS is over full temp range, likely this is not a problem for the DSO
203 which has NO temp rating.

Yes the "72MHz analog" channel rating makes no sense for something sampling at
72MSPS, Nyquist says you get at most 36 MHz bandwith.


That doesn't mean you couldn't use a sampler running at, say, 50 MSPS to 
look at a 110 MHz signal (something we actually do in a radio).


There are lots of ADCs out there that have RF bandwidths of much more 
than the sample rate, intended for use in direct sampling receivers. 
What performance really depends on is how good the sample/hold or 
track/hold is and what the sample jitter is.  (and of course, whether 
there's a stage in front to keep unexpected signals from aliasing in)


There are several ADCs out there that have GHz bandwidths and max sample 
rates in the 100MSPS range.




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Re: [time-nuts] OT - Portable Digital 'scope

[Jim Lux]

On 2/23/12 2:22 PM, Azelio Boriani wrote:

Actually, undersampling does use the alias effect to bring down the RF
carrier. That is, the direct sampling radio concept cannot avoid the
aliasing: it is exploited to avoid, for example, to sample a 2GHz carrier
modulated with a 20MHz signal with a 4Gsample/second ADC (by the way, does
it exist?). A simple 20Msample/second ADC would be enough.


Well.. a 40 MSPS ADC for a 20 MHz wide signal, but yes.

There *are* multi Gsample/second ADCs out there.  ADC12D1800, 12 bit, 
3.6 GSPS.

ADS5400 12 bit 1GSPS
etc



 Yes, to analyze

an analog signal in real time I doubt you can use this method, if the
signal is periodic maybe... you can advance the sampling trigger a bit,
cycle by cycle, and reconstruct the whole signal after this little amount
has covered a full cycle.

That's the way the "sampling head" used for microwaves works (back in 
the day, when tunnel diodes were a new and exotic thing, for instance). 
Still used to today on scopes where they call it things like "equivalent 
time sampling"...


basically a real fast sample and hold, and a not so fast ADC.


There's also clever schemes with fast S/H and multiple interleaved 
ADCs.. but accounting for the tracking errors between ADCs is always a 
chore.


And, various "sub-band-coding" approaches where you subdivide the 
frequency into sub-bands, digitize them in parallel and do fancy math to 
recombine it into a single stream of samples.  If the channelization and 
ADC clocks are cleverly chosen and derived from the same reference, you 
can do quite well (& compensate for differences among ADCs)



The high performance radar processing world is full of this kind of 
thing (look up STAP: space/time adaptive processing).



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Re: [time-nuts] More Static at LightSquared

[Jim Lux]

On 2/28/12 3:40 PM, Chuck Forsberg WA7KGX N2469R wrote:

Does this mean your GPS is safe? Who knows.

http://dailycaller.com/2012/02/28/lightsquared-ceo-resigns-amid-revelations-of-companys-proximity-to-obama-white-house/




well, L2 did just announce they're laying off half their staff (of some 
300+ people). And they missed a big payment to Intelsat last week.  I 
think it's more that the CEO is getting while the getting is good, 
rather than any political machinations.


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Re: [time-nuts] AD9850 boards

[Jim Lux]

On 2/29/12 4:20 PM, Bob Camp wrote:

Hi

They look like part of an eval kit.  The docs on the kit might be out there.

Bob




Like this
http://www.analog.com/en/content/CU_AD9850_evaluation_tools/fca.html

The part has been around a while
"* AD9850 Evaluation Board Software for Windows 3.1
  (zip, 143,708 bytes)

"

*

* AD9850 and AD9851 Evaluation Software Source Code
  (zip, 208,643 bytes)

However I don't see the eval board listed...  The AD9850 is about $15 each

Could be that they dumped all the eval boards...that's probably getting 
to be a 15-20 year old part. (although I think we actually used them on 
some spacecraft radar as a chirp generator.. the partnumber is 
familiar.. maybe SRTM?)





On Feb 29, 2012, at 5:47 PM, Dan Rae  wrote:


On 2/29/2012 1:42 PM, Don Latham wrote:

Dunno if you have seen this on ebay:
260967834514
It's an AD9850 with a 125 MHz crystal mounted up on a .1 spacing board


There are several vendors selling similar things.  I bought a couple and have 
just pulled the 9850 off one for another project of mine.  Build quality is a 
bit odd, and documentation is extremely variable to be polite.

And the 9850 was good :^)

Dan

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Re: [time-nuts] Questions about Austron 5000 Loran C receiver

[Jim Lux]

On 3/3/12 4:13 PM, Azelio Boriani wrote:

Geez, I have read and I don't think it is possible to replicate the CALOC
PDP-8/E software nor it is useful to use the Austron 5000 Loran receiver,
my understanding is that it was used to control and steer the system. It
seems they were in use until the year 2000! Maybe that using MATLAB it is
possible to exploit the Austron 5000 functionality nowadays, provided that,
someway, the 12bit samples from the Austron are transferred to the PC.
Anyway to start with, at least the receiver connectors pinout is
mandatory...



There are PDP8 emulators out there.  Not to mention actual 
microcontrollers that implement the PDP8 instruction set (aside from the 
no-doubt out of production Intersil part).


And a fair number of FPGA implementations in your choice of language.

While it might not be as scenic as that nice plastic see through housing 
with all those discrete DTL circuit cards in the original straight 8.  I 
used a 8/i way back in the early 70s and I was bummed that it was just a 
single box in the rack.


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Re: [time-nuts] Loran in the US

[Jim Lux]

On 3/5/12 2:31 AM, Charles P. Steinmetz wrote:

Poul-Henning wrote:


That would make roll-out a matter not for governments, but for
airports, harbours and other interested parties, like for instance
DME.


Would this mean depending on private parties for precision timing and
positioning [using that particular system, of course]? If so, I'm not
sure that is such a good idea. Some endeavors do not lend themselves
readily to distributed responsibility



But this kind of thing already exists in some ways.  Consider that you 
hire a private party (a licensed surveyor) to establish property 
boundaries and such.  Yes, the surveyor has a legal obligation to report 
their findings to the government (to the county recorder), but I've 
noticed that this isn't always the case.


And until GPS came around, the government was happy to establish a place 
where you could go and compare your clock to an official clock, they 
didn't feel obligated to dstribute time and frequency at high accuracy. 
(Where WWV isn't "high accuracy")


There's also ARINC, which is a private consortium owned mostly by air 
line companies (I think) to provide communications and nav services to 
airliners.


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Re: [time-nuts] Loran in the US

[Jim Lux]

On 3/5/12 3:45 AM, Poul-Henning Kamp wrote:

In message<20120305113804.48fc411b...@karen.lavabit.com>, "Charles P. Steinmet
z" writes:


Technical merit aside, I doubt there is any chance of getting
regulatory approval for such a system, at least in the US, for
practical and political reasons.


Indeed, it's absolutely out of the question, as you well know all
our problems these days are there isn't enough God in the constitution
or something.

Thats why some people in the military is looking into a modern
more lightweight version of "Tactical Loran" for use when GPS is jammed.



What about the Locata folks?  That's a tactical GPS replacement of 
sorts.. precision position and time over a small area (or indoors).


BTW, I think the idea of using PN coded LF or VLF signals is a good one. 
These days, doing the correlation and such is fairly easy.


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Re: [time-nuts] Loran in the US

[Jim Lux]

On 3/5/12 6:19 AM, Charles P. Steinmetz wrote:

Poul-Henning wrote:


Thats why some people in the military is looking into a modern
more lightweight version of "Tactical Loran" for use when GPS is jammed.


That is a much easier thing -- our military/intelligence complex
(however oxymoronic that notion is) tries very hard to keep its
engagements well away from US soil, so (i) no regulatory approval is
required



As someone who deals with non-FCC regulatory approval on a fairly 
frequent basis, I can tell you it's not quite that simple.  If you're 
the US government, you're regulated by NTIA, which works much like FCC 
for licensing.  You have to tell where and when and what sort of 
emissions, where and when and what sort of receivers, get permission, etc.


And if you're planning on operating outside the US, that gets 
coordinated via some ITU process.


This is a HUGE problem for the plethora of colleges, businesses, and 
government labs and research institutions jumping on the nanosat and 
cubesat bandwagon. Their operations don't really fit within the "amateur 
radio" bucket, where licensing is fairly easy.




 and (ii) the geographic area of the operating theater is

usually far smaller than the size of the US. So, we may very well see
the development of mobile beacons for military deployment in hostile
areas, but I very much doubt that we will ever see another terrestrial
beacon system in the US.



Perhaps not a unified one, but I can see a variety of proprietary or 
private locating networks being set up.  Surveyors already have high 
accuracy reference networks.  Some are state run, but others are run by 
consortiums or private parties.  20 years ago, you used to be able to 
subscribe to a private service that would give you differential 
corrections for GPS via a FM broadcast subcarrier or pager.



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Re: [time-nuts] Loran in the US

[Jim Lux]

On 3/5/12 9:26 AM, Chris Albertson wrote:

The best and by far lowest cost solution is to pay TV stations and
maybe AM broadcast stations to add a timing pulse a few times per
second.


I suppose you could do this by the FM subcarrier broadcast approach, 
too.. just like they used to distribute stock quotes, sports scores, and 
GPS differential corrections.


Or, you could use pager transmissions.





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Re: [time-nuts] FCC Chair Talks Spectrum, Gets GPS Letter

[Jim Lux]

On 3/7/12 10:22 AM, saidj...@aol.com wrote:

Sorry for my language, I was quite upset when I read his letter.

If it really was trivial and very low cost to upgrade GPS receivers, then
he should not worry too much about loosing much revenue. This sounds more
like  he made major investments in either Lightsquared itself, or into
designing and  qualifying compatible receivers, and hoping for a major payday 
which
is not  coming.

There should be other solutions for LS such as allocating to a  different sp
ectrum etc to not lose "a $14 billon investment".


I don't think $14B has actually been spent (as in actually paid to a 
manufacturer of parts and/or workers).. sure there's lots of paper 
investments back and forth, but not much cash has changed hands.


We were talking about this at lunch today.. SKyTerra cost something like 
1/2B.  They launched a next gen sat recently (maybe 1B).. I find it hard 
to believe they've spent close to 1B on their test ground stations and 
though they clearly have armies of lawyers and accountants, 1B buys a 
lot of legal fees.


They may well have made commitments and orders for multiple B of future 
purchases, and there will be termination liability if they cancel 
orders, etc.  But again, it's not like they have 1B in their vaunted 
dual mode handset chips sitting in inventory at Qualcomm..





Also his claims that GPS receivers will soon be obsolete anyway's are
clearly not true of course.

This reminds me about the futile episode of Edison electrocuting  Elephants
to prove his DC power grid to be superior to AC...


Those states that use electrocution *do* use AC in the electric chair, 
though... Granted we don't refer to "westinghousing" the offender as 
Edison advocated, though.








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[time-nuts] pointers to information on ways to collect data, 5335, etc.

[Jim Lux]

I've got a student intern (Undergrad Senior) who's doing a project for 
me where he's trying to synchronize (and syntonize) two 1 pps ticks, 
generated from different oscillators using some modules in an FPGA.
One oscillator is a run of the mill 66 MHz clock oscillator the other is 
a 49.x MHz TCXO. (and, of course, because he's working in a breadboard, 
I can swap in a signal generator for either.. I've got a stack of 3325Bs 
and 8663s, etc.)


The objective is to get two signals that are 1 pps  (or 10 pps) ticks 
(each derived from a different oscillator) that align


I'm looking for info to point him to on evaluating the performance of 
his implementation.


I've got a HP 5335 (which works quite nicely with a Prologix and John 
Miles's tools... thanks John!).  I've got oscilloscopes.  I've got 
access to more exotic stuff if need be (although, since my intern budget 
is skinny, stuff I happen to have in the lab, like my uncalibrated 5335, 
is better)


I also have a bunch of Wenzel 10 MHz OCXOs sitting around (although for 
this, why not use one of the instrument's internal oscillator and 
distribute it around)


I do have a hydrogen maser derived reference in the lab, but I'm more 
interested in him measuring the two oscillators against each other. 
(that is, measuring the performance of the TCXO, by itself, isn't 
particularly interesting)



What he needs is some suggestions on things that he can measure that 
would be meaningful figures of merit for the application.


He's not doing a PhD dissertation, though.. And he has to be done before 
the end of the spring semester.  No million second Allan Deviation 
measurements.


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Re: [time-nuts] 5 MHZ PIC PPS Divider?

[Jim Lux]

Quoting John Ackermann N8UR <[EMAIL PROTECTED]>, on Sat 12 Apr 2008  
07:44:06 AM PDT:
>
> * I realize that I'll also be limited by counter resolution.
> 

Unless you use some sort of "time to digital" converter.  There's some  
ASICs out there that do this, and I've seen CPLDs programmed to do it.  
  The new fancy oscilloscopes from,e.g., Tektronix have this so that  
you can measure jitter to finer resolution than the 20Gs/s sample rate.

Seems one could also do a similar Time-to-Digital thing by using the  
old vernier counter scheme.. take your 5MHz and create a slightly  
offset version (4.9,5.1, or 5.01, etc.) by dividing and mixing and  
hook it up to a second counter.

Jim Lux

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Re: [time-nuts] Digital TV signals

[Jim Lux]

Quoting "David I. Emery" <[EMAIL PROTECTED]>, on Tue 15 Apr 2008  
09:18:37 PM PDT:

> On Tue, Apr 15, 2008 at 04:50:29PM -0700, Stanley Reynolds wrote:
>> From: david brown <[EMAIL PROTECTED]>
>> >From a complete amateur, is there any useful timing info to be gained
>> from the newer format of digital tv transmission(Australia) to replace
>> that available from current analogue transmissions.? My recently
>> repaired TV derived frequency standard looks to  be becoming obsolete!
>> David
>
>   > GPS based standard would be the most common now.
>
>   FWIW my understanding is that in the US few local broadcast
> facilities make any very serious attempt to lock their signal timing to
> high accuracy standards or GPSDOs.   Much digital TV broadcast equipment
> is designed so this COULD be done, but there is no current reason to
> spend the money and engineering effort to actually do it -  more likely
> than not signal timing on the output signal is determined by at most a
> medium grade OXCO calibrated every once in while and possibly just a
> TXCO not much better than barely meeting the FCC spec.

If they want to get better coverage, they can transmit from multiple  
sites, all on exactly the same frequency.  The receivers have adaptive  
equalizers (e.g. RAKE)  in them and the multiple identical signals  
just look like multipath, and it coherently combines them.
>
>   So it is not clear that TV signals are good time or frequency
> references any more - though there is little doubt that if there was
> some purpose to doing so both time and frequency could be rather closely
> locked to a GPSDO at the transmitter - it is just with the entire system
> designed to deal with small time, frequency and rate errors at many of
> its interfaces most stations haven't seen fit to implement high accuracy
> frequency or time control on their actual transmitted signal.


It's the multiple transmitters transmitting identical signals  
scenario.. quite unusual in the traditional broadcast environment.


I don't know that anyone is actually doing this, but that's the  
motivation for the synchronization to a gnat's eyelash.  I think there  
are some systems in Europe doing it.

Jim Lux



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Re: [time-nuts] Power monitoring

[Jim Lux]

Quoting Hal Murray <[EMAIL PROTECTED]>, on Thu 17 Apr 2008  
11:10:11 AM PDT:

> My power went out the other day.  That reminded me that I've always been
> slightly curious about that area.
>
> Are there any not-expensive boxes made for this?  Or something that shows up
> on eBay occasionally?

Lots of dataloggers out there in the <$200 range.
Check out things like the HOBO from Onset.

you can also get embedded style computer from someone like Tern or  
Z-world or Vesta that has all the hardware needed, and comes with some  
basic software that you could use.

>
>
> If I was doing it myself, I'd start with a low power (quiet) PC and a UPS.

Battery and single board computer or data logger is much better...  
such an application doesn't need a video monitor, keyboard, etc.


> Then I'd have a platform that could monitor other things too, like
> temperature.
>
>   Step 0 is just to measure when power is/isn't there.
> I assume the UPS has a signal for that.
>
>   Step 1 is to measure the voltage.
> This takes an A/D.  The standard PC audio input might be appropriate.

no DC coupling on the audio card.  Much better to either get something  
with the appropriate A/D OR a "one-wire" style interface.

You could transformer down the 60 Hz, digitize as an audio signal, and  
process it appropriately.

> I'd probably use an AC wall-wart transformer for isolation and a couple of
> resistors to get down to a reasonable voltage.
>
>   Step 2 is to catch dips and spikes.
> That's just software behind the A/D.  (assuming the A/D is fast enough)
>
>
> As long as I'm dreaming...  Suppose I wanted to measure the power my whole
> house is drawing.  What's available along the lines of a current transformer
> on the main lines?  My first thought is that nobody does that (for homes) so
> it's probably horribly expensive.  On the other hand there is a lot of
> interest in energy conservation these days so it might only be somewhat
> expensive.

Lots of these available, in the few hundred dollar range..

http://www.powercostmonitor.com/p3982/power_cost_monitor.php
http://www.theenergydetective.com/index.html

you can also do something like watch the wheel goaround on the meter  
with a photocell
or
put a suitable current transformer ($5 surplus, $50 new) on the mains  
coming in.



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Re: [time-nuts] Frequency reference

[Jim Lux]

Quoting Attila Kinali <[EMAIL PROTECTED]>, on Sun 20 Apr 2008 05:50:21 AM PDT:

> On Thu, 17 Apr 2008 08:47:48 -0700 (GMT-07:00)
> "Richard W. Solomon" <[EMAIL PROTECTED]> wrote:
>
>> You can build a very good GPSDO for about $100 in parts.
>
> Stupid question, but if one builds his on frequency
> reference, how can you be sure it's acurate and precise?


not a stupid question at all..PhD dissertations have been written  
about answering it.

>
> Or to but it in other words: how do you measure self build
> devices?

Build 2 or 3, and compare them against each other. (can't have too  
many frequency and time standards...)


or, take it to somewhere that has a higher quality standard and compare

or, just trust that the performance is inherent in the design, and if  
it works at all, it's good enough. Typically, if you are building a  
copy of a known good design, this is a good start.


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Re: [time-nuts] Frequency reference

[Jim Lux]

Quoting Attila Kinali <[EMAIL PROTECTED]>, on Sun 20 Apr 2008 04:23:38 PM PDT:

> On Sun, 20 Apr 2008 09:25:37 -0700
> Jim Lux <[EMAIL PROTECTED]> wrote:
>

> Well.. then you have to build multiple frequency sources
> that exhibit different physical behaviour, otherwise
> slight changes in the enviroment that degrate your
> precision will go unnoticed (ie, if all sources have
> the same temperature coefficient then temperature
> changes will affect all of them the same way making
> you unable to measure this effect)

A good point..  One might, for instance compare your OXCO source  
against GPS 1pps ticks.


>
>> or, take it to somewhere that has a higher quality standard and compare
>
> Which is quite difficult if you don't have access to a physics
> lab which you can use for a few days to weeks.

Indeed..

>
>> or, just trust that the performance is inherent in the design, and if
>> it works at all, it's good enough. Typically, if you are building a
>> copy of a known good design, this is a good start.
>
> I'm an engineer, i don't trust anything i cannot measure,
> because i know that errors and mistakes are inherent in any design :-)


True enough, but I suspect you are willing to trust a design to some  
point (perhaps not to it's design precision, but some lesser level),  
as long as the design is such that errors in function are knowable(as  
opposed to just larger measurement uncertainty).

And, you probably trust others to make some of the measurements. For  
instance, you probably trust the mfr of your inch/cm scale to some  
precision (i.e. you don't have a primary length standard sitting in  
your garage.. although on this list, one can't be too sure..).

>
>   Attila Kinali
>
> --
> The true CS students do not need to know how to program.
> They learn how to abstract the process of programming to
> the point of making programmers obsolete.
>   -- Jabber in #holo
>



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Re: [time-nuts] Whispering Gallery-Mode....??

[Jim Lux]

At 10:02 AM 4/24/2008, you wrote:
>In message <[EMAIL PROTECTED]>, "David C. 
>Partridge" writes:
> >>From the paper:
> >>From the paper:
> >
> >"... can be understood by comparison with the optical concept of "total
> >internal reflection," or by the acoustic "whispering gallery"phenomenon
> >experienced in large circular halls."
> >
> >The classic whispering gallery is in St. Paul's Cathedral, London.   If you
> >stand near the wall on one side, you can hear someone standing in a similar
> >location on the other side even when they talk very quietly - hence the term
> >whispering gallery.
>
>
>It was my impression that the resonators which operatte in WG mode
>uses the _other_ pecularity about whispering galleries, an effect
>very few people even know about, reasons which will be obvious in
>a moment:
>
>Empty the entire gallery of as much absorbant material as possible,
>including people and their clothes.


Fascinating stuff..


See also a paper by Georg Essl in Acuostics Research Letters Online 
[DOI:10.1121/1.1929347]

"Whispering" waves and Bate's ridges in numerical experiments

He refers to some papers by Rayleigh (hey, how often do you get to 
cite Rayleigh in a paper?)



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Re: [time-nuts] Disciplining Rubidium

[Jim Lux]

At 02:29 PM 4/24/2008, [EMAIL PROTECTED] wrote:
>Hi Tom,
>
>that Superstar receiver only has +/-50ns 1PPS timing accuracy (typical).
>That compares to an M12M claimed accuracy of +/-10ns corrected.
>
>I wonder why the receiver manufacturers don't do the math on the carrier
>phase, and generate very accurate 1PPS signals. Is it because they 
>don't have
>OCXO's? Or do they need the data from USNO to do the math?

Money?  There's not much demand for cheap receivers better than 50ns, 
so a mfr isn't going to spend the time and money to do it.

Other uncertainties (multipath, ionosphere, phase center movement 
with look angle, etc) are of that general magnitude as well, so even 
if your little receiver could put out a 1pps with 1ns accuracy, the 
other parts of the system are worse.

A bit of system engineering would show that there's not much market 
for a $100 receiver that has to be hooked up to a $4000 choke ring 
antenna, for instance.

Certainly, for the hacker market, one might see this (if for no other 
reason than you could build your own antenna, or at least, the chokes)


>
>Is there any public domain software that can take the carrier phase data,
>and give you a solution, at least a position fix with 1cm accuracy etc?


You might start here:
http://gipsy.jpl.nasa.gov/orms/index.html


>
>As far as I know the M12+ was tested at USNO to within 2ns average over 300
>hours, and I have never seen a better timing receiver measurement. But that
>still is 2 Feet accuracy, a far cry from 1cm.
>
>thanks,
>bye,
>Said
>



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Re: [time-nuts] Disciplining Rubidium

[Jim Lux]

At 04:04 PM 4/24/2008, Bruce Griffiths wrote:
>Jim Lux wrote:
> >
> > Other uncertainties (multipath, ionosphere, phase center movement
> > with look angle, etc) are of that general magnitude as well, so even
> > if your little receiver could put out a 1pps with 1ns accuracy, the
> > other parts of the system are worse.
> >
> >
>Jim
>
>Receiving antenna phase centre movement will only be a few cm not meters.
>Also the phase centre position is highly repeatable and once calibrated
>can easily be corrected for.
>Even the phase centre movement of the SV transmitting antenna (typically
>a helical antenna array) can be modelled.
>
>Multipath has a relatively small effect on a carrier phase disciplined
>oscillator.
>
>Correction of the ionosphere propagation delay correction can take
>advantage of the difference between the ionosphere's group and phase
>velocities.
>Only a single frequency receiver is required for this.
>
>However generating an accurately positioned PPS pulse is another matter
>entirely as code phase data is required.
>
>Bruce


I agree with you..

I think my comment was more that the cost of dealing with all those 
other factors (calibrateable or compensateable) is big enough or rare 
enough that there's not much commercial market for a inexpensive 
receiver that has, say, 1ns, accuracy.

Add that to the all around hassle (as you've described) of trying to 
accurately position a pulse to a fraction of a clock coming from an 
ASIC that is clocked at around 10-20 MHz.


Jim 



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Re: [time-nuts] 100 MHz Source

[Jim Lux]

At 09:46 AM 4/29/2008, Richard W. Solomon wrote:
>I need a 100 MHz source to lock up a F/W brick. I have 10 MHz available
>
>from my GPSDO. Anyone know an easy way to get 100 MHz using the 10 MHz
>
>source ? Maybe another PLO ?
>
>If I multiply then I need some pretty decent filtering which might 
>be difficult.


Straight multiplication is probably cleanest.  A x5 followed by a doubler.

Yes, you'll need some filtering, but not too much.
>

Jim Lux



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Re: [time-nuts] sub cables

[Jim Lux]

At 06:05 PM 4/30/2008, Didier Juges wrote:
>Interestingly, my company just received an RFQ for DC/DC converters 
>for trans-oceanic cables. Interesting specification. Among other 
>things, 2,000,000 hours MTBF (the converters are multi-redundant) 
>and, I like that part, 100% altitude tested :-) Something else you 
>might find interesting: all repeaters are daisy chained. The power 
>comes from two current limited 1A 10,000V supplies, a positive one 
>at one end, and a negative one at the other end, so that if the 
>cable is grounded accidentally in the middle (say, by a boat anchor, 
>just a guess...) all the repeaters still get power. One supply can 
>power the entire cable. Two grounds, and you can lay another cable. 
>The power return is through the earth. Don't swim near a head-end 
>cable... The capacitance of the cable is measured in Farads, and it 
>takes several hours to charge the cable at power up. Some time ago, 
>we bid on the head-end power supplies (we did not get that job). It 
>is interesting to observe that high reliability has a different 
>meaning in the under-sea cable business and in the military airborne 
>business. We do the latter. Didier KO4BB


I would think that the undersea cable and the deep space robotic 
exploration business have similar philosophies.  Long life, 
inaccessibility for repair, etc.

Jim Lux



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Re: [time-nuts] Optical time sync

[Jim Lux]

At 11:54 PM 5/1/2008, Hal Murray wrote:

> > I assume that this would have to be locked to the grid frequency
> > somehow  - can't see all that power being rectified then sent out
> > through a  grid-locked inverter.
>
>Why not?
>
>Diesel-electric locomotives do electrical conversions because it's more
>efficient than mechanical gears.
>
>Some high voltage transmission lines are DC.  The conversion sites on each
>end must be interesting.


And makes it much easier to stabilize the power flow between 
regions.  (A 2000 km long transmission line makes for all sorts of 
interesting things with reactive sources at one end and reactive 
loads at the other).

The Pacific DC Intertie terminates at Sylmar (in the San Fernando 
Valley, about 20 miles north of downtown Los Angeles).. +/-500kV at 3000A.

They just recently (last 10 years) changed from mercury pool 
inverters to solid state thyristors.  Both are quite impressive.




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Re: [time-nuts] Measuring 10 MHz accurately.

[Jim Lux]

At 10:20 AM 5/7/2008, Ulrich Bangert wrote:
>Martyn,
>
>2 parts in 10E-12 in a second's gate time would require to measure the
>time interval with an 2 ps resolution. Since the SR620 (at least mine)
>features a 20 ps single shot resolution, i fear your number is more
>likely "20 parts in 10E-12". Or what you are doing is to make >= 10
>measurements / s of phase and computing the arithmetic mean of them.

For example, the implication is that the SR620's timebase is accurate 
to parts in 1E-12 or 1E-13, so that it can count off that 1 second 
with suitable accuracy.



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Re: [time-nuts] "Piezo Little Wonder" OCXO

[Jim Lux]

At 08:33 AM 5/30/2008, you wrote:
>Early GPS receivers used a 10.23 MHz time base.
>Probably related to 2^10-1.


yep.. the chip rate for the C/A code is 1.023 Megachips/second, the P 
code is 10.23 Megachips/second, and the L1 frequency (1575.42) is 
exactly 154 times the 10.23 MHz, the L2 is 120 times.
So you can see that having a 10.23 MHz oscillator is a handy thing in 
a GPS receiver, especially if you can discipline it with the received signal.

These days, one might choose a reference oscillator somewhat higher, 
so that when you do your 1bit A/D of the signal, you get many 
samples/chip, and so that the signal directly aliases to somewhere 
convenient. A lot of receivers use a sampling clock such that you get 
1 bit I and Q samples at a convenient sample rate.  4*10.23 would 
work nicely, eh?  40.92 MHz



>Some GPS manufacturers approached HP about making
>a 10811 on 10.23 MHz.  There is a circuit modification
>for 10.23 MHz and some crystals were made (I
>have some somewhere).  However, I don't believe
>any 10.23 MHz 10811's were sold.  This unit was
>probably intended to meet the need not filled by HP.



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Re: [time-nuts] "Piezo Little Wonder" OCXO

[Jim Lux]

At 10:37 AM 5/30/2008, you wrote:
>I have two PIEZO 10.230 MHz crystal oscillators in the same style package as
>the 10811.  But the oscillator in question is for 10.238 MHz.


interesting.. is the 8kHz a deliberate offset?  Is the manual tuning 
off to one end? Maybe they were using them in a scheme where instead 
of I/Q they did offset IF sampling.




>John  WA4WDL
>
>- Original Message -----
>From: "Jim Lux" <[EMAIL PROTECTED]>
>To: "Discussion of precise time and frequency measurement"
>
>Sent: Friday, May 30, 2008 12:47 PM
>Subject: Re: [time-nuts] "Piezo Little Wonder" OCXO
>
>
> > At 08:33 AM 5/30/2008, you wrote:
> >>Early GPS receivers used a 10.23 MHz time base.
> >>Probably related to 2^10-1.
> >
> >
> > yep.. the chip rate for the C/A code is 1.023 Megachips/second, the P
> > code is 10.23 Megachips/second, and the L1 frequency (1575.42) is
> > exactly 154 times the 10.23 MHz, the L2 is 120 times.
> > So you can see that having a 10.23 MHz oscillator is a handy thing in
> > a GPS receiver, especially if you can discipline it with the received
> > signal.
> >
> > These days, one might choose a reference oscillator somewhat higher,
> > so that when you do your 1bit A/D of the signal, you get many
> > samples/chip, and so that the signal directly aliases to somewhere
> > convenient. A lot of receivers use a sampling clock such that you get
> > 1 bit I and Q samples at a convenient sample rate.  4*10.23 would
> > work nicely, eh?  40.92 MHz
> >
> >
> >
> >>Some GPS manufacturers approached HP about making
> >>a 10811 on 10.23 MHz.  There is a circuit modification
> >>for 10.23 MHz and some crystals were made (I
> >>have some somewhere).  However, I don't believe
> >>any 10.23 MHz 10811's were sold.  This unit was
> >>probably intended to meet the need not filled by HP.
> >
> >
> >
> > ___
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> >
>
>
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Re: [time-nuts] PCB design questions thread II

[Jim Lux]

At 06:05 PM 6/2/2008, you wrote:
>Bob Paddock wrote:
>
> >>> 2. How many layers?   In an ideal world with money no object, if I
> >>> understand the current art correctly, I think I'd probably aim for a five
> >>> layer
> >
> > I assume that is a typo?  You can not have an odd number of layers.
> > In this current 3D reality each layer has two sides.  :-)
>
>
>Sure you can.  I have done 3 layer, 5 layer, and 7 layer boards.
>
>Having done those, I will advise you not to do 3 layer, it warps.  But
>everything else is easily do able.
>
>6 layer can be made by:
>
>2 side | 0 side | 2 side | 0 side | 2 side
>...
>
>The only down side to odd numbers of layers is the supply house
>has to stock 1 sided laminate.

or etch ALL the copper off one side of two sided..

Jim 



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Re: [time-nuts] USB to Serial Connectors for GPS Modules

[Jim Lux]

At 04:10 PM 6/5/2008, Matthew Smith wrote:
>Quoth Ulrich Bangert at 2008-06-05 13:58...
>
> > consider the latency times of ANYTHING on a USB provided virtual serial
> > connection to be in the order of 1 ms. If no serial data is send but
> > only status signals change their state the latency can even be higher.
>
>Thanks (and to the others who responded to this).  Just wanted to know
>where I was.
>
>I will make sure that I've got "real" serial ports with "real" kernel
>drivers for timing applications and use USB only for non time-critical
>stuff, like control messages, etc. (given a module with with 2 serial
>ports and only 1 port available on the house computer, for instance.)
>
>Cheers
>
>M


I wouldn't assume that the latency on a hardware serial port, 
depending on the OS, is any better than 1 ms, either.

Particularly if you are expecting the process to be something like:

value change on serial port line (Carrier Det)
interrupt from hardware
fielded by serial port ISR
blocked process waiting on CD interrupt marked as ready to run

process starts running.

While it might only take microseconds to fire up the ISR, it could be 
milliseconds before your process starts to run (unless you're using 
something at the device driver level?)






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[time-nuts] cesium clocks..

[Jim Lux]

OK.. if one wanted a cesium reference in one's garage (just because  
it's something you should have.. that GPSDO depends on outside  
influences, after all)

what's the typical budget for getting one of these beasts used, and  
where does one find one (Ebay? A time-nuts subscriber in a back alley  
with a password?)

Jim


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Re: [time-nuts] cesium clocks..

[Jim Lux]

Quoting Jim Palfreyman <[EMAIL PROTECTED]>, on Thu 19 Jun 2008  
09:27:12 PM PDT:

> Jim,
>
> If you're searching Ebay, just make sure you don't accidentally buy a
> Nike brand of shoe...
>
> Jim Palfreyman

Well... in fact, that's sort of the question I'm asking. if one does  
search Ebay, what's an effective search term?

Leaving aside the $60 Nike Cesiums...




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[time-nuts] Rb references for audiophiles?

[Jim Lux]

For your amusement...

Sitting in a waiting room yesterday, I read an article in a  
very-high-end audio magazine describing a $15K Rubidium frequency  
standard for providing low jitter clocks to your audio system.  It has  
outputs at 44.1, 48, etc. kHz, as well as a 100kHz, which the person  
writing said might become a new standard (huh?)

Aside from the usual blather about how the improved clock jitter made  
this album or that more open sounding and improved the auditory  
experience, there were the usual gold plated connectors, etc.

Hey... here's a golden opportunity for a time nut.  I suspect they  
generate the various clocks using (gasp) digital dividers and such.   
Now's your chance to design an incredibly complex all analog synthesis  
chain with step recovery diodes, mix and add, etc.   Everyone knows  
that for the finest in audio, an all analog (preferably all Class A)  
design is essential. Make sure that you have at least one vacuum tube  
in the design, preferably two, that can be "hand selected" and mounted  
so there's a little window to see the glow, and have some nice analog  
meters to monitor some useless parameter (suppressor grid voltage or  
something)

I don't know where they get Rubidium, but maybe you could market a  
concept of terroir (as for wine).. why, the Mark 3000 Rubidium  
reference source uses Rb extracted only from the finest hand selected  
ores from Canada, where they have been mined by miners with multiple  
generations of experience, using trucks fueled with, etc...


Or following on the more recent discussions on the list about Cs and  
NH3 references, maybe you can one-up the Rb maker with a Cs.

Or maybe GPS disciplined clock sources (you know... if the 44.1kHz  
sample stream coming off the CD isn't precisely aligned on the second,  
sonic quality is definitely impaired.. the only real question is  
whether you should have a means of adjusting the clock rates to  
accommodate small changes in the earth's rotation or relativistic  
effects.


A whole magazine, 100 pages long, filled with this sort of thing (and  
yes, they had the special speaker cables with the arrows to indicate  
preferred direction of power flow, too)

Jim


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Re: [time-nuts] Rb references for audiophiles?

[Jim Lux]

Quoting [EMAIL PROTECTED], on Fri 04 Jul 2008 08:01:04 AM PDT:

>
> In a message dated 04/07/2008 14:51:19 GMT Daylight Time,
> [EMAIL PROTECTED] writes:
>
> Sitting  in a waiting room yesterday, I read an article in a
> very-high-end  audio magazine describing a $15K Rubidium frequency
> standard for  providing low jitter clocks to your audio system.  It has
> outputs at 44.1, 48, etc. kHz, as well as a 100kHz, which the person
> writing said might become a new standard  (huh?)
>
>
>
> 
> Any chance you can remember the name and/or issue number of the  magazine?

I think it was "absolute audio"...

I think it's this unit they were reviewing
ESOTERIC - G-0Rb MASTER CLOCK GENERATOR (RUBIDIUM)

which oddly, is actually made by a division of Teac
http://www.teac.com/esoteric/
http://www.teac.com/esoteric/Master-Clock_Up-Converter.html

There's also this:
http://forum.cakewalk.com/tm.asp?m=1304280



Oh.. maybe it it was in "The Absolute Sound" Mar 2008


Anyway, the data sheet does mention
... both have an input port cabale of receiving a 10 MHz reference  
signal from an external component.  This port can be connected with  
devices such as an ultra-precise cesium atomic oscillator as a "system  
upgrade" for special applications.

(and, yes, the are proprietary gold plated BNC ports)


As for my previous speculation about GPS disciplined sources... why  
yes, they are also made... excellent...  I guess those guys at  
Teac/Esoteric haven't got on that bandwagon yet.


Fascinating, too, that they don't actually have any real data on the  
jitter performance of their box on the spec sheet.. even though that's  
what they're selling.. they just quote the absolute frequency accuracy.

That's enough for now... I have to get my special green marker to  
treat the edges of all my CDs to reduce extra internal reflections,  
and then I have to patch the air bladders on the vibration isolating  
optical table I have the CD player set up on (granted my first CD  
player could really have used this...)






>
> No, I don't want to buy or build one, but I'd love to read a copy of  that
> article:-)
>
> regards
>
> Nigel
> GM8PZR
>
>
>
>
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Re: [time-nuts] Rb references for audiophiles?

[Jim Lux]

Quoting Mark Sims <[EMAIL PROTECTED]>, on Fri 04 Jul 2008 04:02:49 PM PDT:

>
> Bahhh,  a TRUE audiophile has three H-masers.  You just can't trust   
> your favorite recording of Thick as a Brick to a single reference   
> clock.  You need a realtime thee-cornered hat voter/selector to   
> chose the best one.  But masers do meet the number one audiophile   
> requirement of a having a glowing vacuum tubey thingy.



Voter?  But that's digital.  You mean a totally analog combiner that  
optimizes the overall variance.  See, there IS a use for that old  
analog computer plugboard you scavenged in 1970.  (Of course, you WILL  
be using Philbrick OpAmps with the vacuum tubes like the ones Bob  
Pease is always talking about)

Jim

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Re: [time-nuts] Rb references for audiophiles?

[Jim Lux]

Quoting Greg Burnett <[EMAIL PROTECTED]>, on Fri 04 Jul 2008 11:54:35 AM PDT:

> ---Jim wrote:
> ...they had the special speaker cables with the arrows to indicate
> preferred direction of power flow, too)
> ---clip---
>
> Jim, "directional" audio interconnect cables typically have two conductors
> for the signal path, plus a shield. The shield is connected at only the
> "destination" end of the cable. This is similar to some low-level
> instrumentation connections (where the signal flows through two inner
> conductors, and we don't want the shield contributing to circulating AC
> ground currents).

That one I'm familiar with.. (SpaceWire cables, for instance, have 4  
shielded twisted pairs, 2 in each direction, with the shields grounded  
at the sending end for each pair of pairs)...


These were just plain old two (gold/palladium plated) pins for each  
"cable" (granted, the cable is some complex braided combination of  
silver ribbons, which is a fairly exotic form of Litz wire, I  
assume... but no shield)




>
> The situation for "directional" speaker cables is a bit stranger, but,
> again, typically involves a shield connected at only one end of the cable.
>
> --Greg
>
>
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Re: [time-nuts] Rb references for audiophiles?

[Jim Lux]

Quoting Bruce Griffiths <[EMAIL PROTECTED]>, on Fri 04 Jul  
2008 05:47:53 PM PDT:

> Jim Lux wrote:
>>
>> That one I'm familiar with.. (SpaceWire cables, for instance, have 4
>> shielded twisted pairs, 2 in each direction, with the shields grounded
>> at the sending end for each pair of pairs)...
>>
>>
>> These were just plain old two (gold/palladium plated) pins for each
>> "cable" (granted, the cable is some complex braided combination of
>> silver ribbons, which is a fairly exotic form of Litz wire, I
>> assume... but no shield)
>>
>>
>>
> Unless each individual strand is insulated from all the others (as it is
> in true Litzendraht) braiding the wire is ineffective in reducing skin
> effect.
>
> Bruce

It was unclear from the literature I saw, but I have to assume that  
they know this (Litz wire and all it's properties have been  
"fashionable" in one sense or another for the audiophile biz for  
decades... I had friends who made their own).  On the other hand...


I did run across an interesting product for high end audio (not  
recently)... air core tape wound inductors (i.e. a pancake shaped coil  
with the winding of thin tape, instead of wire) in both silver and  
copper.  Very interesting stuff.   A friend was looking at using them  
for magnets for a rail gun type system (since they have have a hole in  
the middle for mounting)...

Jim


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Re: [time-nuts] Frequency divider design critique request

[Jim Lux]

At 10:41 AM 7/11/2008, David C. Partridge wrote:
>M
>All,
>
>CPLD - wassat?  OK, OK I have some idea, but that's about all I know.
>Anyway these are probably BGA stuff which I couldn't hope to hand solder
>anyway - it's enough of a stretch for me to think of hand soldering this SMT
>board.

CPLD -> small programmable logic device (think like a PAL, but 
bigger).. not BGAs, typically.  Anywhere from a dozen to a couple 
hundred gate equivalents.  Some are really, really fast (e.g. 1 ns 
prop delays, etc.)





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Re: [time-nuts] Thunderbolt - temperature

[Jim Lux]

At 03:37 PM 7/11/2008, Didier Juges wrote:

>On the other hand, I think it would be very well advised to place the unit
>in a quiet area with minimal temperature changes, like you would do to keep
>a good bottle of wine.

I knew that putting my Z8301 in the wine locker in the garage was a 
good idea. It was the coax gods who caused that to be the only place 
that I could put it which the cable from the antenna would reach, but 
clearly, they were thinking ahead.

Jim






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Re: [time-nuts] precise external reference time for a PC

[Jim Lux]

Quoting Marc Balmer <[EMAIL PROTECTED]>, on Sat 12 Jul 2008 04:55:08 AM PDT:

> Hi all,
>
> for an upcoming experiment I am looking for precise external
> time reference, preferrably an atomic clock that I can hook
> up to a computer running a Unix variant.
>
> I should be able to read out the time with a low latency, e.g.
> over PCI or PCI-e bus.
>
> The time reference will serve me as a, well reference, to
> calibrate a series of various radio clocks.
>
> I am looking for used equipment, it should fit in a hobbyists
> budget,  sth. in the 1000-5000$ range would be nice, but it
> should be as precise as possible.
>
> If you have ideas or pointers for me, that would be very
> welcome.


there are a variety of cards made that can generate/receive timecode  
or sync pulses that plug into a PC.  True-Time (now Symmetricom) used  
to make an IRIG timecode card for ISA bus, for instance.  I imagine  
these are in the $1000 range.

For instance the National Instruments PCI-6601 counter timer card is  
about $350

Then, drive that with Rb standard from Stanford Research (I seem to  
recall seeing ads on the back of Electronic Design or some such for  
$1795)...

That's all brand new.  One can do much better if one hunts down  
surplus or used.

Jim



>
> Thanks,
> Marc Balmer, HB9SSB
>
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Re: [time-nuts] Double ovened 10811-60158 on ebay

[Jim Lux]

Quoting Mark Sims <[EMAIL PROTECTED]>, on Sat 12 Jul 2008 09:12:34 AM PDT:

>
> Remember that heat flow is proportional to the FOURTH power of the   
> temperature difference.

Heat transferred by *radiation* goes as the 4th power.  Heat  
transfered by conduction goes linearly.  Unless you're in a vacuum,  
conduction might dominate.



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Re: [time-nuts] thermal transfer - even a little further OT

[Jim Lux]

Quoting Mark Amos <[EMAIL PROTECTED]>, on Sat 12 Jul 2008 10:13:36 AM PDT:

> Timenuts,
>
> In introductory texts regarding the FFT there is some mention of   
> Fourier's studies having had something to
> do with heat transfer.  Yet most of the FFT work I've been exposed   
> to has to do with decomposing signals
> into component sinusoids, translating between time and frequency domain, etc.
>
> Does anyone have a "layman's" explanation of how this relates to   
> what Fourier was trying to do with heat
> transfer?

M. Fourier was looking at the problem of heat transfer in cannon  
barrels, which, in 2D is a ring (aka a continuous periodic function).

http://en.wikipedia.org/wiki/Joseph_Fourier has more info (including  
the interesting thing that I didn't know before, about his discovery  
of the greenhouse effect)

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Re: [time-nuts] PLL Math Question

[Jim Lux]

On 3/12/14 10:06 PM, Chris Albertson wrote:

On Wed, Mar 12, 2014 at 9:13 PM, Daniel Mendes  wrote:

This is a FIR x IIR question...

moving average = FIR filter with all N coeficients equalling 1/N
exponential average = using a simple rule to make an IIR filter


Isn't his "moving average" just a convolution of the data with a box car
function?  That treats the last N samples equally and is likely not
optimal.   I think why he wants is a low pass filter.


A moving average (or rectangular impulse response) *is* a low pass 
filter.  The frequency response is of the general sin(x)/x sort of 
shape, and it has deep nulls, which can be convenient (imagine a moving 
average covering 1/60th of a second, in the US.. it would have strong 
nulls at the line frequency and harmonics)



This method is like

the hockey player who skates to where to puck was about 5 seconds ago.  It
is not the best way to play the game.  He will in fact NEVER get to the
puck if the puck is moving he is domed to chase it forever..   Same here
you will never get there.


That distinction is different than the filter IIR vs FIR thing. Filters 
are causal, and the output always lags the input in time.  if you want 
to predict where you're going to be you need a different kind of model 
or system design.  Something like a predictor corrector, for instance.






But if you have a long time constant on the control loop you have in effect
the kind of "averaging" you want, one that tosses out erratic noisy data.
A PID controller uses only three memory locations and is likely the best
solution.


PID is popular, having been copiously analyzed and used over the past 
century. It's also easy to implement in analog circuitry.


ANd, there's long experience in how to empirically adjust the gain 
knobs, for some kinds of controlled plant.


However, I don't know that the simplicity justifies its use in modern 
digital implementations: very, very few applications are so processor or 
gate limited that they couldn't use something with better performance.


If you are controlling a physical system with dynamics that are well 
suited to a PID (e.g. a motor speed control) then yes, it's the way to 
go.  But if PIDs were so wonderful, then there wouldn't be all sorts of 
"auto-tuning" PIDs out there (which basically complexify things by 
trying to estimate the actual plant model function, and then optimize 
the P,I, and D coefficients).


PID controllers don't do well when there's a priori side knowledge 
available.  For instance, imagine a thermostat kind of application where 
you are controlling the temperature of an object outside in the sun. 
You could try to control the temperature solely by measuring the temp of 
the thing controlled, and comparing it against the setpoint (a classic 
PID sort of single variable loop).  Odds are, however, that if you had 
information about the outside air temperature and solar loading, you 
could hold the temperature a lot more tightly and smoothly, because you 
could use the side information (temp and sun) to anticipate the 
heating/cooling demands.


This is particularly the case where the controlled thing has long time 
lags, but low inertia/mass.




We have to define "best".  I'd define it as "the error integrated over time
is minimum".  I think PiD gets you that and it is also easy to program and
uses very little memory.  Just three values (1) the error, (2) the total of
all errors you've seen (in a perfect world this is zero because the
positive and negative errors cancel) and (3) the rate of change in the
error (is it getting bigger of smaller and how quickly?)  Multiply each of
those numbers by a constant and that is the correction to the output value.
It's maybe 6 or 10 lines of C code.   The "magic" is finding the right
values for the constants.


And that magic is sometimes a lot of work.

And practical PID applications also need things like integrator reset to 
prevent wind-up issues, and clamps, or variable gains.


PID, or PI, is, as you say, easy to code, and often a good first start, 
if you have a system with fast response, and lots of gain to work with. 
 It's like building circuits with an opamp: big gain bandwidth product 
makes it more like an ideal amplifier where the feedback components 
completely determine the circuit behavior. Put in hysteresis, or a time 
delay, and things start to not look so wonderful.





This is worth reading
PIDforDummies.html 



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Re: [time-nuts] Power Supply for AD9852 / AD9854

[Jim Lux]

On 3/16/14 8:13 AM, d0ct0r wrote:


Thanks ! Looks like I am on the right track.
I've attached couple of documents which could be useful. I'am going to
use two separated voltage regulators for VCC/AVDD and DVDD. And use 10
Ohm / 100Mhz  ferrite board and few capacitors to "separate" VCC and AVDD.




those parts dissipate a fair amount of heat, and they're not very big.
If you turn on everything in the 9854 AND run it at 300 MHz clock, it 
draws about 1.2 Amps (@ 3.3V) which is about 4 Watts.. that's a lot of 
power to get out of the part and keep Tj reasonable. Board layout to get 
the heat out is very important.  If they get too hot, they start to act 
flaky.  You get extra spurs and more importantly, they don't respond to 
the programming properly (e.g. you send the serial stream to program 
frequency X, and instead it programs some different frequency).



"The heat sink of the AD9854ASVZ 80-lead TQFP package must
be soldered to the PCB. "

"Adequate dissipation of heat from the AD9854 relies on all
power and ground pins of the device being soldered directly to
a copper plane on a PCB. In addition, the thermally enhanced
package of the AD9854ASVZ has an exposed paddle on the
bottom of the package that must be soldered to a large copper
plane, which, for convenience, can be the ground plane."


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Re: [time-nuts] Power Supply for AD9852 / AD9854

[Jim Lux]

On 3/16/14 9:34 AM, d0ct0r wrote:



I would assume that using two voltage regulators will spread the load.
For the AD9851 I'am planning to put external radiator glued on top of it.



It's not the power dissipation of the regulators that's the concern, 
it's the dissipation of the 9854.  A heatsink on top doesn't do much for 
it, since the thermal path is out through the bottom and/or the leads. 
Of course, if your regulators are sharing the thermal path, then 
dissipation in the regulators becomes a concern too.


Read the data sheet and the ap note for details.

The eval board works OK most of the time. I've encountered flaky 
behavior but that could have been from other causes.


The 9854 is the part that was used in the Flex-Radio SDR1000, but most 
of the options were powered off, so the dissipation was in the <1 watt 
range. That particular board would overheat in an enclosure if you 
didn't have a fan blowing on it.

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Re: [time-nuts] NIST time services

[Jim Lux]

On 3/18/14 10:18 PM, Tom Van Baak wrote:

If you can design a system that can handle 6.5 billion requests per day, this 
opportunity is for you...


https://www.fbo.gov/spg/DOC/NIST/AcAsD/RFI_InternetTimeServiceComments/listing.html

Solicitation Number: RFI_InternetTimeServiceComments



For those that are unfamiliar with the ways of US Government 
contracting, this is NOT a request for proposals to provide the service. 
It's more of a preliminary step to identify potential bidders, gather 
background information, shake the trees to find out who the potential 
players are, as well as help make a decision on whether it's even a good 
idea.  (e.g. it might feature into a make vs buy report)


We do this at NASA when we want to make sure we haven't missed something 
in the marketplace.  These days, Government folks don't go to as many 
conferences and almost no trade shows.  So you find out what's available 
by exercising google or bing, which is not such a great way to find 
niche products and services.  Someone who's got a great way to do 
reliable, accurate time distribution over the internet might not have a 
big web presence, or might be overshadowed by something similar that has 
been heavily Search Engine Optimized.


This is also a way for people who aren't necessarily interested in 
providing the service to give comments to NIST about potential issues 
that may be of concern.  Those kinds of comments might wind up changing 
the eventual procurement, or might even result in a report that says 
"nope, not worth privatizing this, because of reasons A, B, and C". 
that's the crux of question 7 at the end "What are advantages and 
disadvantages of NIST's potential transition of time services from a 
NIST-only service to private sector operation..."



A lot of the questions at the end of the RFI are things that get 
discussed on time-nuts from time to time.



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[time-nuts] Fwd: Re: NIST time services

[Jim Lux]

 Original Message 
Subject: Re: [time-nuts] NIST time services
Date: Wed, 19 Mar 2014 10:21:17 -0700
From: Jim Lux 
To: time-nuts@febo.com

On 3/19/14 9:50 AM, Chris Albertson wrote:

So they want to in-invent NTP?

I think NTP already services way more than 6.5 billion per day.  The
problem with NTP is while it is nearly optimal and provides the best
time accuracy for a given hardware/network setup it is not technically
"traceable" even if the time really is from NIST indirectly.



They are well aware of NTP.. they serve 6.5 billion a day *from NIST*
and that's what they are looking at potentially outsourcing or changing.

And, of course, there's the "legally traceable" aspect.



I think you could fix this traceability problem with some rules about
how to write the configuration files, no new software.   For example
NTP already handles cryptographic authentication.   Make the use of
this monitory so that then you know you are talking to a NIST
referenced server.


That's very possible, and you could respond to the RFI and tell them so.
Could you set up a legally traceable set of multiple tiers?
What would the mechanics of this be?

That's really what the RFI is all about.. "tell us what you think we
need to know"..

They'll get responses that are overlapping existing knowledge, for sure.

And nobody is going to respond with something that is confidential or
proprietary or telegraphs a future product line, because all the RFI
responses are essentially public info.



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Re: [time-nuts] Aircraft ping timing

[Jim Lux]

On 3/19/14 5:21 PM, Bill Hawkins wrote:

They only got one ping from INMARSAT at 64E above the Indian Ocean.
There was no other ping to triangulate the position.

One ping projects a circle on the Earth. The maximum flying range of the
plane determined the ends of the NE and SE arcs of that circle.

The news only gets stranger as time goes on.



not time based...from what I understand it's based on a received power 
estimate, matched against antenna patterns.


Not particularly accurate.  The power measurement is probably good to 
0.2 dB (at best).  If the transmit antenna's attitude isn't in the 
nominal straight and level (e.g. plane is banking, or parked on ground, 
perhaps with a tarp placed by a overweight gentleman holding a white 
furry cat on his lab?)


I did some back of the envelopes and there's a good many 100s of km 
uncertainty in range.


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