Re: [time-nuts] Why are 1PPS signals so skinny?

2012-05-15 Thread Mark J. Blair

On May 14, 2012, at 09:33 , b...@lysator.liu.se wrote:
 More modern 3-5.5V into 50ohm, 20us.
 
 http://contracting.tacom.army.mil/majorsys/jab/DAGR%20Interface%20Specification.pdf


Is a similar standard available for the older PLGR devices?

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Re: [time-nuts] New unit of time measurement

2012-01-15 Thread Mark J. Blair

On Jan 14, 2012, at 23:12 , Poul-Henning Kamp wrote:
 You are not the first researcher of this interesting phenomena:
 
 http://www.washingtonpost.com/opinions/cellphone-ban-would-be-a-distraction/2011/12/16/gIQAdv2GyO_story.html


Article states: Upon arriving at a red light, drivers apply the brakes, pick 
up their mobile devices, and begin reading and sending e-mails. The signal to 
resume driving comes not from the green light but from some motorist in the 
back tapping politely on the horn.


This is why I begin honking immediately after stopping. It removes the latency, 
which can otherwise be annoying at a light with a short green cycle. :-)



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Re: [time-nuts] Thunderbolt Supply

2011-02-12 Thread Mark J. Blair

On Feb 10, 2011, at 3:16 PM, Larry McDavid wrote:
 I'm seeking a recommendation for a power supply for this Thunderbolt receiver.

I use an HP 6236B that I bought inexpensively on eBay, after reading about 
others having good results with that combination. I had to repair it (it had 
one or two bad caps), but it was still inexpensive after the cost of the 
components. The TBolt draws more than the supply's rated current on the +12V 
output during cold start, but neither the TBolt nor the power supply seem to 
mind, and the operating current settles down into the supply's normal operating 
range after a few minutes of warm-up.

I have the TBolt bolted right on top of the supply (over the coolest corner). 
This is far from ideal, but the supply's ventilation holes are conveniently 
spaced to line up with the T-Bolt's mounting holes. I'll improve my setup 
eventually, when I feel a surge of time-nuttiness coming on. :) Even in its 
current configuration, it far exceeds my needs for a frequency reference.

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Re: [time-nuts] Thunderbolt Supply

2011-02-12 Thread Mark J. Blair

On Feb 12, 2011, at 11:03 PM, Kevin Rosenberg wrote:
 Exceeding your needs? Doesn't seen like that surge of time-nuttiness has hit 
 yet ;)


Don't worry, I'm just pacing myself. :)

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Re: [time-nuts] worth salvaging ?

2011-01-29 Thread Mark J. Blair

On Jan 29, 2011, at 6:43 AM, paul swed wrote:
 It seems to interpret the almanacs wrong because amazingly enough its
 actually does know the correct GPS week which was a shock to me. Unless
 thats a simple calculation from the date I might guess.

It's the other way around: The GPS week is directly decoded from the GPS 
signal. If I'm not mistaken, the GPS week roll-over causes a problem of being 
able to correctly calculate the calendar date from the GPS week. I could be 
mistaken, but I think that a receiver that doesn't handle the rollover properly 
but is otherwise in good shape should be able to track satellites and provide a 
correct position, but the calendar/clock time calculation would be wrong.

In a receiver that doesn't have a recent almanac, and particularly in an older 
receiver that takes a very simple approach to downloading ephemeris and almanac 
information, initial acquisition could take a long time. It'll need to do a 
slow full-sky search for its first satellite, and older receivers couldn't do 
that nearly as quickly as newer ones can. Once it gets that first bird, it may 
sit there downloading ephemeris and almanac data for at least 12.5 minutes 
before it does anything else. With an old receiver from that era, give it at 
least a half hour of good open-sky conditions before you begin to suspect that 
it's dead.


Back to the original topic now: That OCXO may seem mundane by time-nutty 
standards, but I'd certainly consider it to be worth salvaging. It could have 
all sorts of applications for radio stuff, portable test equipment, and even 
time-nutty stuff in an application that wants to be smaller and more portable 
than a Rb standard or full GPSDO.

I also agree that there's likely to be a lot more salvageable stuff on those 
boards. I see lots of socketed parts. UV-erasable EPROMs are worth saving. Are 
those Altera parts reprogrammable? If so, then they're worth keeping. Keep any 
microcontrollers or CPUs that are reprogrammable, or rely on external program 
memory, or can still be used in spite of fixed internal programming (e.g., an 
old mask-programmed 8051 can be used as an 8031 by strapping a pin to tell it 
to ignore its mask ROM and use external program memory).

I'd say that any units which track satellites at all after a half hour should 
be considered for repair, and the rest of the units are goldmines of parts.



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Re: [time-nuts] worth salvaging ?

2011-01-29 Thread Mark J. Blair

On Jan 29, 2011, at 4:03 PM, David Martindale wrote:
 It all depends on the receiver firmware. [...]
 In a little while, Garmin released a small utility that you
 ran on a PC connected to the GPS via its serial port, and it reset
 something that allowed the GPS to do a successful cold start.  I
 remember an rumour that it simply reset the saved date and time far
 enough away that the receiver dumped all its old almanac entries,
 forcing it to do a cold start that worked.


Ah, yes. If the receiver is too stubborn to give up and do a very cold start, 
then it may single-mindedly continue searching exactly where the satellites 
aren't!


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Re: [time-nuts] Frequency based on mobile services

2011-01-25 Thread Mark J. Blair

On Jan 25, 2011, at 7:25 AM, Raj wrote:
A thought occurred to me that there should be a way to lock our 
 OCXO/TCXOs to cell phone services signals that that is present almost 
 everywhere. I am not conversant with cellular technology so I am curious!
 
Any ideas and/or thoughts?

There's a software tool called Kalibrate for use with the GNU Radio software 
and USRP radio hardware, which uses GSM base station signals as a standard to 
measure the frequency offset of the USRP's oscillator. It's not really a 
time-nutty application, but it serves as an example of using cellular base 
stations as a frequency reference.

  http://thre.at/kalibrate/
 

GNU Radio is a free open-source development environment for implementing 
software-defined radios. The USRP is one of the more popular RF hardware 
options for use with GNU Radio.

  http://gnuradio.org/redmine/wiki/gnuradio

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Re: [time-nuts] GPS Antenna -Receiver Mutual Interference...

2011-01-03 Thread Mark J. Blair

On Dec 30, 2010, at 6:53 PM, Burt I. Weiner wrote:
 Has anyone run into a situation where two GPS Navigation type 
 Antenna/Receivers interfere with each other?

It's possible that LO leakage from one is jamming the other. When doing mobile 
GPS receiver testing at work with a single antenna feeding multiple receivers 
through a splitter, we sometimes had to insert attenuators in each receiver's 
antenna feed to keep them from jamming each other.

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Re: [time-nuts] GPS Antenna -Receiver Mutual Interference...

2011-01-03 Thread Mark J. Blair

On Jan 3, 2011, at 1:00 PM, Burt I. Weiner wrote:
 I'm not sure of the nature of the two receivers, but using conventional 
 receiver design thinking, the only thing that comes to mind that might be 
 radiating would be the oscillators or possibly the I.F. section taling to 
 each other.

My company's earlier GPS receivers used a frequency plan with the IF at around 
2 MHz, so the LO was well within the passband of the SAW filter and common 
patch antennas (both typically have passbands around 5 MHz wide, IIRC). Thus, 
we had quite a bit of LO leakage then. While our own receivers generally didn't 
mind sharing an antenna through a simple splitter, we tended to have trouble 
when doing this with a mixture of our own receivers and some of our 
competitors' receivers. Some combinations apparently resulted in LO leakage 
from our receivers causing problems for our competitors' receivers. While 
there's something to be said for jamming one's competitors, this prevented us 
from gathering the comparative data that we needed. :)  We fixed this with the 
simple expedient of putting an attenuator on each splitter output to reduce 
cross-coupling.

I haven't been directly involved in receiver testing for a while, but I think 
that we now use a higher IF, and thus I'd expect that we get a lot less LO 
energy leaking out through the front end.

In any given setup involving multiple GPS receivers sharing an antenna and/or 
located close to each other, you may or may not have problems. It'll depend on 
the particular combination of receivers, the LO frequencies, how much LO leaks 
out of each one, whether that LO leakage lands in a bad spot for any of the 
other receivers, how much isolation is between the receivers, etc.


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Re: [time-nuts] beats was Re: If there a FAQ

2010-11-30 Thread Mark J. Blair

On Nov 30, 2010, at 8:42 AM, William H. Fite wrote:
 I expect you can do the same thing with an electric fan.

Or by chewing something crunchy (like ice) while watching a raster-scanned 
(CRT) television.




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Re: [time-nuts] A real-world precision timing need....

2010-10-31 Thread Mark J. Blair

On Oct 31, 2010, at 8:06 AM, Bob Camp wrote:
 Adequate protection starts at about 1 of steel plate if it's angled to the 
 incoming projectiles.  

Using hardened armor plate (as used for steel gong targets) can get that down 
under a half inch, resulting in a lot less mass to drag downrange and back. It 
won't hurt to locate the sensor behind a berm, either. The sky screen and/or 
its supports will still get shot eventually, but that will be a lot cheaper to 
replace than the sensor.



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Re: [time-nuts] A real-world precision timing need....

2010-10-31 Thread Mark J. Blair

On Oct 31, 2010, at 7:21 PM, Bob Camp wrote:
 The gotcha is that the gong can move / twist when hit.  The plate buried in 
 front of the electronics has to just sit there and take it. More energy 
 transfer to the anchored plate. 
 
 I'm sure there are alloys that will get you under 1, the issue will be 
 making sure you have the right one...

Ah, good point. Also, it won't matter if the steel stops the bullet from 
penetrating if the shock turns the enclosed electronics and optics into powder.

As an aside, when I bought my high power rifle rated steel gong target (which, 
sadly, I haven't taken for a test drive yet), I looked at pre-shot samples from 
about four different vendors who had displays at the gun show, and there was a 
noticeable difference in the steels that they used. The vendor I chose had 
little more than faint dimples surrounded by lead spatters where .308 rounds 
allegedly hit their target, while other vendors had substantial craters.

Back to the topic at hand: If muzzle velocity and time of flight alone would 
provide enough data (*), then one possibility would be a downrange target with 
an attached transducer (piezo?) to register the bullet impact, with a wire pair 
going back to the shooting bench. In this case, the downrange sensor would be 
cheap to replace when it eventually fails, and all of the expensive/delicate 
stuff would be back at the shooting bench.

(*) I haven't studied ballistic equations carefully enough yet to know whether 
this would provide enough information to estimate fun details like ballistic 
coefficient.



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Re: [time-nuts] Determining Time-Nut infection severity.

2010-10-24 Thread Mark J. Blair

On Oct 24, 2010, at 1:44 PM, Richard H McCorkle wrote:
 The disease will continue to progress until
 ultimately all of the patients personal time and money are
 exhausted or they die.



One can only hope that the local coroner is also a Time-Nut, so that time of 
death can be determined with suitable accuracy and precision. Does anybody know 
how many bits of precision are used on tombstones these days?


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Re: [time-nuts] Determining Time-Nut infection severity.

2010-10-24 Thread Mark J. Blair

On Oct 24, 2010, at 1:58 PM, Poul-Henning Kamp wrote:

 In message 53601812-fc62-4098-9266-55edf50af...@nf6x.net, Mark J. Blair 
 wri
 tes:
 
 Does anybody know how many bits of precision are used
 on tombstones these days?
 
 Most tombstones are engraved with CNC machines and while I have yet
 to see a company advertise it as a competitive parameter, your vital
 lack of stats will be engraved with better than 1/50mm precision.


Oh, I was mostly concerned with the bits of precision used for the birth and 
death timestamps.



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Re: [time-nuts] Determining Time-Nut infection severity.

2010-10-24 Thread Mark J. Blair

On Oct 24, 2010, at 2:03 PM, Magnus Danielson wrote:
 The real mourning of the deceased from fellow time-nuts comes when they 
 realize just how much of precious gear has been lost forever.

Of course, we would like to know precisely when the precious gear was lost.


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Re: [time-nuts] Determining Time-Nut infection severity.

2010-10-24 Thread Mark J. Blair

On Oct 24, 2010, at 3:36 PM, mike cook wrote:
 A nut in the final stages of the disorder  would  request to be buried with 
 their clocks . The lab would be sealed for eternity.

In that case, I'd better rush out and patent tombstones with integrated GPS 
antennas for entombed GPSDOs. I'll make millions on the licensing fees, thus 
funding the H-maser that I'll be buried with.

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Re: [time-nuts] I have a new toy

2010-10-24 Thread Mark J. Blair

That sounds (and looks) thoroughly delightful! With a proper external 
reference, you'll be able to synthesize another reference at *precisely* the 
wrong frequency. :)

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Re: [time-nuts] GPS backup for the stationary time and frequencyuser

2010-10-09 Thread Mark J. Blair

On Oct 9, 2010, at 12:47 PM, jimlux wrote:
 Simple GPS jammers are pretty easy, since consumer GPS is very vulnerable to 
 repeater jammers.  Hmm I wonder if that would adversely affect a GPSDO?  
 Probably not, since the repeated signal is just as stable as the original one.

I would think that with a little bit more effort, one could make a fairly 
simple repeater jammer that broadcasts a substantially less stable signal. With 
a suitable slack buffer between the receiver and transmitter, the 
retransmission delay doesn't need to be constant or even predictable, thus 
messing with apparent time and frequency. With still more effort, one could 
detect individual satellite signals and retransmit them separately with 
different and varying delays, thus messing with the apparent position 
relationships of the birds at any point in time.



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Re: [time-nuts] GPS backup for the stationary time and frequencyuser

2010-10-08 Thread Mark J. Blair

On Oct 8, 2010, at 10:27 AM, J. Forster wrote:
 GPS needs several birds to lock up,

To get a position fix, this is true; 3 birds minimum for a 2D fix, 4 birds 
minimum for a 3D fix.


 and if you look at a single bird, Dopplar will make the signal useless as
 a frequency reference.

Only if you don't already know your position. Once your position has been 
determined accurately and you have the current ephemeris data for the bird 
you're listening to, you can factor out the predictable doppler and use a 
single bird for timing and frequency.



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Re: [time-nuts] GPS backup for the stationary time and frequencyuser

2010-10-08 Thread Mark J. Blair

On Oct 8, 2010, at 10:44 AM, J. Forster wrote:
 KISS. This seems like a lot of work for not particularily good results.
 Among other things, you have no closure so no measure of how good your
 measuremwent is.

Single-satellite timing mode is already commonly implemented in timing 
receivers; there's no work to be done other than turning it on. Closure is only 
lacking if all of the USAF ground stations are taken out such that the 
ephemeris and health information can no longer be updated on any intact birds; 
otherwise you know where every existing bird is at any instant in time, and 
each bird indicates whether it should be trusted.

Bottom line: If there's still one intact bird and one intact ground station to 
control it, you can get accurate time and frequency whenever it's visible 
(assuming no local jamming/spoofing) if you've already surveyed your position, 
using off-the-shelf hardware like a TBolt.

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Re: [time-nuts] 60 KHz Receiver

2010-10-05 Thread Mark J. Blair

On Oct 5, 2010, at 1:15 PM, shali...@gmail.com wrote:
 That is basically the sauce behind GPS. What is the power of the transmitters 
 on the satellites? It can't be much, and the signal on the ground is quite a 
 bit below the noise floor before correlation.

If I recall correctly, the transmit power is around 15W. A received signal of 
-130dbm is considered strong, and tracking (but not acquisition or data 
decoding) can still be done at signals approaching -160dbm.


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Re: [time-nuts] antennas

2010-09-27 Thread Mark J. Blair

What is the purpose of the temperature sensor chip on the PCB, anyway? Isn't 
the temperature inside the OCXO much more important?

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Re: [time-nuts] [qs1r] Looking for good, cheap, external reference

2010-09-22 Thread Mark J. Blair

On Sep 22, 2010, at 5:57 PM, Bob Camp wrote:
 The temp sensor is the one that moves in real small steps. The bad one moves 
 in (1/2 degree???) big steps. 
 
 All of that (and much more) is visible if you bring up Lady Heather and see 
 what's going on.


My TBolt has the 3.0 firmware and the silver Trimble-marked OCXO. As I recall, 
Lady Heather plots the temperature with the scale set as small as 5 
millidegrees C per division when the temperature isn't moving around too much. 
Does that mean that I got lucky and got one with the good temperature sensor, 
new firmware and good OCXO?

BTW, I fixed the crashing issue I had previously mentioned. It turned out that 
my HP 6236B supply from eBay had a bad filter cap in the 5V supply, causing it 
to have poor load regulation and a lot of ripple, and in turn causing the 
TBolt's power supervisor to randomly trip. Now that I've replaced the cap I 
managed to complete a 48-hour survey, which I wasn't able to do before. Hooray!


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Re: [time-nuts] [qs1r] Looking for good, cheap, external reference

2010-09-22 Thread Mark J. Blair

On Sep 22, 2010, at 7:50 PM, Ed Palmer wrote:
   Does the temperature move around a little or is it a flat, straight
   line?  If it never moves, it's probably the bad one.  As Bob mentions
   below, the temperature only changes in large steps with the bad
   sensor.  The good one has steps in the millidegree range.  I got my
   chips from the auction place.  Make sure that they are C or D revision,
   the E revision is the bad one.  Check the list archive for lots of info
   on this topic.

It does move around, so I think I have the good one. I should be powering it 
off soon to do some more work on the power supply, so I can open it back up to 
check the temperature sensor revision.



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Re: [time-nuts] Thunderbolt initial check out?

2010-09-19 Thread Mark J. Blair

On Sep 19, 2010, at 4:38 PM, Bob Camp wrote:
 Lady Heather is a good program to dig into a TBolt with. It's free...

It also plots oscillator and PPS error (the oscillator error plot may be off by 
default). If the error plots look good and both signals can be seen at the BNC 
outputs with an oscilloscope (and everything else reads green, of course), 
then I'd say that your Tbolt is likely to be in good shape.



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Re: [time-nuts] Timing Distribution in Mountainous Terrain

2010-09-10 Thread Mark J. Blair
I presume that there's a good reason for the selection of antenna sites which 
don't have LOS to each other. However, would it be possible to select 
additional sites at which to install repeaters to allow timing calibrations to 
be made between pairs of primary receiving sites? These repeaters could also 
provide backup communications so that a primary receiving site isn't 
necessarily taken out of action if its communication channel (wireline?) gets 
cut by a wandering backhoe. Each repeater site would be selected to have LOS to 
two or more primary receiving sites, or when that's not possible, to one 
primary receiving site and another repeater that can see a different site.

While multiplying the number of sites wouldn't be cheap (even considering that 
the repeater sites may host much less expensive equipment than the primary 
receiving sites, and may be able to operate without wireline communications or 
power lines to the sites), it might be cheaper than installing hydrogen masers 
and radio telescopes, designing custom aircraft and flying them overhead every 
20 minutes, etc.


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Re: [time-nuts] Timing Distribution in Mountainous Terrain

2010-09-10 Thread Mark J. Blair

On Sep 10, 2010, at 10:47 AM, Pete Rawson wrote:
 Can you use tethered balloons at each site to obtain adequate S/N
 in their position to permit time calculations to 30ns uncertainty?


Tether a single balloon to three sites to reduce the balloon's displacement due 
to wind, and then measure its position relative to the three sites by laser or 
radar ranging! :-D




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Re: [time-nuts] Timing Distribution in Mountainous Terrain

2010-09-09 Thread Mark J. Blair


On Sep 9, 2010, at 10:42, Ralph Smith ra...@ralphsmith.org wrote:

 Paranoia. People making the requirements are concerned with GPS going away
 due to solar flare or some other reason.

Hmm... So the decision makers think that after a solar flare or some other 
reason (hostile destruction of the birds, perhaps?) takes out the GPS system, 
it'll be back up and running within six days? That sounds optimistic to me. 

It sounds to me more like you would need to function indefinitely without GPS, 
and just use GPS for initial position survey and as a convenient way to 
synchronize to external time reference (with ground-based backup methods in 
place and periodically tested). 
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Re: [time-nuts] Timing Distribution in Mountainous Terrain

2010-09-09 Thread Mark J. Blair

On Sep 9, 2010, at 12:03 PM, Ralph Smith wrote:
 1e-11 only buys you 3000 seconds of drift before blowing the 30 ns budget.
 Without going to cesium we will most likely need some form of mutually
 visible synchronization.

How about a rubidium or cesium standard at each site for holdover, with an 
extra cesium standard that is physically carried from site to site (say, by 
helicopter) during an extended holdover period to distribute a common time 
reference around?

Or, a specially-equipped aircraft which is periodically flown along paths 
visible to multiple antenna sites during an extended holdover in order to 
adjust out drift based on measured round-trip times between the sites and 
aircraft? In effect, flying your own low-altitude satellite over the sites when 
the GPS system is down.

These may be silly ideas, but brainstorming is fun.



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Re: [time-nuts] What position is measured?

2010-09-07 Thread Mark J. Blair

On Sep 7, 2010, at 6:30 AM, jimlux wrote:
 Another analogy is that if you had a machine that recorded all the signals, 
 mounted right at the antenna, and then carried the recording half way around 
 the world, and then ran the recording into a receiver, it would give you the 
 position of the antenna, not the receiver.  The cable is just a time delay.

Does this mean that while the antenna feedline cable length does not influence 
the measured position (at the phase center of the antenna), and it does not 
influence the accuracy of a disciplined frequency reference output, it does 
introduce an error into the absolute time output (i.e., adding a delay to the 
PPS output)?

In other words, do I correctly assume that I may safely ignore the length of my 
TBolt's antenna feedline if I am only interested in its 10 MHz OCXO output, but 
I may want to compensate for it if I ever find a need to use its PPS output as 
an absolute time marker?

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Re: [time-nuts] What position is measured?

2010-09-07 Thread Mark J. Blair

On Sep 7, 2010, at 5:16 PM, jimlux wrote:
 Yes.. except that the cable's physical and electrical length *do* vary with 
 temperature, so if you're looking at the gnat's eyelash sort of thing, you 
 need to take that into account.  Maybe 10 ppm/degree, so a 20 meter run will 
 change a bit less than a millimeter.  That's down in the fractional 
 picoseconds time-wise.
 
 It's an issue if you're doing things like interferometry at higher 
 frequencies..


I see a bright future selling oven-controlled speaker cables to audiophiles... 
;-)


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Re: [time-nuts] Maser info (vacuum levels)

2010-09-02 Thread Mark J. Blair

On Sep 2, 2010, at 10:28 AM, Corby Dawson wrote:
 This EFOS maser typically runs with the two vacuum pressures below 1.5 X
 10-6 Torr. (as measured via the ion pump current)
 
 Maximum should not exceed about 3.6 X 10-6 Torr for either pump.
 
 The internal vacuum will drop to about 1 X10-7 Torr if the Hydrogen to
 the disassociator is turned off.


Back in college, I took a semiconductor device physics course which included a 
lab where we made simple ICs (the most complex devices were SR latches). We had 
a vapor deposition system for plating on gold or aluminum, which pumped the 
chamber down below 10E-12 Torr as I recall, within ten minutes or so after a 
clueless freshman opened the beast up and tossed in a bit of aluminum or gold 
wire and a few chunks of silicon with their grubby hands (ok, we used tweezers, 
but still...). The whole unit was about as big as a refrigerator or two. It 
used a rotary-vane roughing pump and an oil diffusion pump with a liquid 
nitrogen trap. This was about 25 years ago.

Reading here about the troubles of pulling a very good vacuum, I'm now 
wondering what sorts of painful engineering went into making the machine 
turn-key and freshman-proof? It's entirely possible that I've mis-remembered 
the pressure level, but that's the exponent that stuck in my mind for whatever 
reason.

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Re: [time-nuts] WeirdStuff tbolt $75 [eBay Link]

2010-09-02 Thread Mark J. Blair

On Sep 2, 2010, at 10:06 AM, Oz-in-DFW wrote:
 http://cgi.ebay.com/300457580821
 
 And still more than 10 available.


That listing appears to have ended. If I had gotten there in time, I'd have 
been tempted to buy a couple of them. My Thunderbolt is flaky (stops outputting 
serial data or responding to serial commands after a period of minutes to 
hours), so I could have tried out a couple others in hopes of finding a 
reliable one, followed by harvesting OCXOs from the ones that didn't make the 
cut.




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Re: [time-nuts] Maser info (vacuum levels)

2010-09-02 Thread Mark J. Blair

On Sep 2, 2010, at 12:00 PM, Scott Newell wrote:
 I think I took that same class (sub-basement of Steele, right?) just a few 
 years after you.

That would be the one! See, I knew that most anybody who attended that 
particular institution would recognize my description of that piece of 
equipment. I took the classes in '86-'87. I would have been class of '90 if I 
hadn't flunked three quarters of math and two quarters of physics... but the 
lure of the device physics lab was enough incentive for me to bludgeon my brain 
into passing that pair of device physics courses. I also thoroughly kicked butt 
in the freshman-level digital electronics courses, which oddly enough were 
easily as advanced as the junior-level digital electronics courses that I 
eventually took at UC Irvine. A big portion of my career naturally has involved 
digital ASIC design, since that and software development appear to be the 
things that I can idiot-savant my way through while only understanding enough 
math to be able to count to 1! :-)

What house were you in? I was in the red one, with a guest membership in the 
black one due to my disrespect of security devices and interest in telephone 
switching networks. Have you ever followed the yellow brick road to cold under 
Arms?


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Re: [time-nuts] Have Quick Tools

2010-08-23 Thread Mark J. Blair

On Aug 23, 2010, at 7:52 AM, Brooke Clarke wrote:
 Has anyone made a PIC based Have Quick device to either compare two have 
 quick outputs, generate a HQ data stream or read a HQ stream?

I've been interested in playing with the HQ outputs of my HQ-compatible GPS 
receivers for a long time. It's on my list of things to do before the heat 
death of the universe, but there are a lot of projects ahead of that one.

Not that it matters since there are so many projects ahead of it, but if I was 
going to do this today I'd probably use a TI MSP430 family processor, since 
those are what I'm presently set up to develop for. Hmm, maybe one could set up 
one of those Chronos wristwatch development kits to automatically set the watch 
time from a HQ source over its wireless link? You know what they say: Measure 
it with a micrometer, mark it with a chalkline, and cut it with a chainsaw! :-D


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Re: [time-nuts] Have Quick Tools

2010-08-23 Thread Mark J. Blair

On Aug 23, 2010, at 11:29 AM, Pieter ten Pierick wrote:
 I would just use an axe for that, much less precise };-P
 And of course for the measuring I would use a laser interferometer based
 system, with nm precision!


I suggest replacing the chalkline with one of those inverted spray cans for 
painting markings on the ground, then. Because the chalkline string would block 
the laser beam.




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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-21 Thread Mark J. Blair

On Aug 20, 2010, at 11:17 AM, Rick Karlquist wrote:
 The AMC-123 can also be homebrewed by reading the
 patent, which is listed on the data sheet.

I found it here:

http://www.freepatentsonline.com/3624536.pdf

Having read the patent, I find I'm still weak enough in the area of discrete 
amplifier design that I'd have low confidence of creating an amplifier with the 
required phase noise, gain, isolation and compression specifications. Assuming 
the simple amplifier in Figure 1, I think I'm make or break the design (more 
likely the latter) by selecting a suitable in-production replacement for the 
2N5109, figuring out the required turns ratio of autotransformer L1, biasing 
the transistor amplifier correctly, etc.

I'd have no problem building it; if I identified off-the-shelf magnetics then I 
could even build a whole bunch of them, as I design PCBs for a living (mostly 
GPS stuff; I can lay out the microwave stuff as long as a smart RF guy comes up 
with the necessary LNA circuit topology), and I even have a bit of experience 
designing mechanical stuff (i.e., in case it wanted to be in a nice machined 
aluminum shield/heat-sink box, though my CNC mill is presently in pieces so I'd 
need to farm out mechanical fabrication). I'm just weak in the analog/RF design 
area so far.

Since the Q: Which amplifier? A: AMC-123! thing appears to be a FAQ, and that 
patent may be old enough to have expired, I wonder if the world wants a nice 
plug-and-play TIME-NUTS-123 amplifier based on the Norton patent, designed with 
currently-available off-the-shelf components (aside from the custom PCB and 
possibly enclosure), which could be made in smallish batches, characterized by 
somebody with the right equipment, and sold at a reasonable price to help folks 
cobble together their home-brewed phase noise measurement and frequency 
reference distribution systems.

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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-21 Thread Mark J. Blair

On Aug 20, 2010, at 3:41 PM, Rick Karlquist wrote:
 It might still be available through Tyco/MAcom.  They have continued to
 make selected Anzac components.  There was also an AM-123, which
 was a TO-something can version.

My first quick scan didn't turn up any offered for sale, though I did dig up 
the datasheet:

http://pdf1.alldatasheet.com/datasheet-pdf/view/184840/MACOM/AM-123/+074853VKvwOxcER.tvC+/datasheet.pdf


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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-21 Thread Mark J. Blair

On Aug 20, 2010, at 5:11 PM, John Miles wrote:
 Also, it looks like you (Mark) are only about an hour from Cerritos, where
 the MUD ( http://www.microwaveupdate.org ) conference will be held at the
 end of October.  This could be one option for you.  As part of the $35
 registration cost, you get access to a test lab set up to help attendees
 measure noise figure, PN, etc. on any homebrew or commercial gear they wish
 to bring.

Interesting. I still think I'd like to be able to measure low phase noise 
signal sources at home if practical. In particular, I've been toying with the 
idea of starting my own little company on the side, making and selling 
ham-radio-related/test-equipment-related stuff that seems to be missing from 
the market, as a (probably small but hopefully positive) secondary source of 
income and an excuse to design, build, accumulate (and deduct!) fun electronic 
equipment. My desire to learn to characterize phase noise stems from the idea 
that some of my products would be things whose phase noise should be specified, 
and it wouldn't be right for me to leech off other people's test equipment and 
effort if I plan to make a buck at it. Thus, I feel the need to learn how to do 
it myself, and then use that ability to add some value to the world in some 
manner.



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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-21 Thread Mark J. Blair

On Aug 21, 2010, at 12:04 PM, Bob Camp wrote:
 There are a number of articles on the web detailing the art of getting one of 
 these to work. Since it's broad band feedback you need to be a little careful 
 with the layout and the transformer.

Thanks, I'll continue digging.



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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-21 Thread Mark J. Blair

On Aug 21, 2010, at 12:10 PM, Adrian wrote:
 It's still being made by Tyco / MaCOM:
 http://www.macomtech.com/datasheets/AM-123_AMC-123.pdf

Thanks! According to Avnet (the only one of their US distributors where I found 
a price posted online), the price is around $600 each at quantity 5 for the SMA 
connector version.

!!

I think I'll continue investigating a homebrew implementation for now!



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Re: [time-nuts] Antenna problems

2010-08-21 Thread Mark J. Blair

On Aug 21, 2010, at 7:15 PM, Peter Krengel wrote:
 Warren found out that the signals  TB gets out of my small ceramic typ 
 antenna are too weak. They are too noisy.
 
 So I had a look for a good antenna and found some commercial typs called
 choke-ring antenna. As they are really expensive is there any DIY solution
 avaliable? 

I think that the TBolt wants a fair amount of gain up at the antenna, based on 
the signal levels it reported from the roof antenna feed at work (we're in the 
GPS industry) compared to what I normally see from our normal GPS receivers. 
Mine is installed at home with a Lucent/Alcatel +26dB antenna which I believe 
was primarily intended for use at cellular base stations, and my TBolt sees 
nice, strong signals from it with about 9m of feedline. These antennas are all 
over eBay, both used and unused, and with or without the pole mount. The TBolt 
will power them with its +5V bias. An eBay search for lucent gps antenna 
should turn up a few antennas and several mounts at the moment.

There are probably many other antennas that will work fine. I'd suggest looking 
around for active GPS antennas meant for outdoor fixed installations (they'll 
generally have a somewhat pointy radome to keep snow, birds, etc. from 
accumulating on them), powered by +5VDC, and with at least 20dB of gain. Used 
ones can be cheap.


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Re: [time-nuts] (no subject)

2010-08-20 Thread Mark J. Blair

On Aug 20, 2010, at 5:07 AM, Bob Camp wrote:
 The TBolt OCXO does have good noise characteristics. Unfortunately you have 
 to pull it out of the unit to figure that out.

Is its phase noise substantially worse when it's in the unit? I.e., is the rest 
of the TBolt adding a lot of phase noise to its output via its power and/or 
tuning voltages?

I'm powering my TBolt with an HP 6236B bench supply rather than the cheap 
open-frame switcher that came with it. Based on what I read, powering the TBolt 
with a switcher adds a lot of noise/spurs to the OCXO spectrum. My unit has the 
Trimble-marked OCXO, which I gather is supposed to be a lot better than the 
Piezo-marked one. My TBolt is presently just screwed onto the top cover of the 
6236B, which is probably far from optimal. I have the whole setup installed in 
a closet, so at least it doesn't get nailed with a blast of cold air every time 
the air conditioner turns on.



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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-20 Thread Mark J. Blair

On Aug 20, 2010, at 4:56 AM, Grant Hodgson wrote:
 You've come to the right place - well, that is if you want to devote a 
 significant amount of your life in the pursuit of ever-more accurate time and 
 frequency measurements

:)

 If you've only got one source then you need to use the frequency 
 discriminator method (aka delay line method) of phase noise measurement.  
 Basically you take the output of the source, split it in two, delay one of 
 the signals, re-combine the two and then measure the resultant signal on a 
 base-band spectrum analyser.
[...]
 The limitation of the frequency discriminator method is that the noise floor 
 of the measurement system is often worse than the DUT, especially if your DUT 
 is very good, and it's even worse if you're trying to measure close-in noise. 
  The Sherer article gives a good graph illustrating this. If you're trying to 
 measure the phase noise of the oscillator inside a Tbolt then I don't think 
 that a frequency discriminator will be sensitive enough, although I might be 
 wrong.


I got the impression that for good OCXOs like the HP 10811 or (supposedly) 
the OCXO in my TBolt, the delay line method wouldn't provide enough sensitivity 
for measuring close-in phase noise.

 Despite what you said, you might want to consider buying an HP 10811 
 oscillator or similar which you could use in a phase detector measurement 
 system which is likely to give superior results.

I might need 2 or 3 of them so I can weed out the under-performers! :) I had 
originally considered getting one of the surplus HP/Agilent GPSDOs with HP 
10811 OCXOs, but I settled on the TBolt since it appeared to be almost as good 
(in terms of phase noise), a bit cheaper, and a bit easier to power than one of 
the HPs that need 48VDC. Well, I bought another power supply for the TBolt, 
anyway, but at least it would be easier to build a power supply that operates 
from +12VDC, a voltage that's always available in a ham shack.






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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-20 Thread Mark J. Blair

On Aug 20, 2010, at 7:40 AM, Adrian wrote:
 - you may build your own HP 3048A alike system, but be prepared to invest 
 serious money and time, and much more time than you thought in the 
 beginning... (if that is what you're after, you'll have the most fun you can).

I did a quick survey of surplus phase noise measurement system prices on eBay, 
and was shocked by how cheap they apparently aren't. I'll set up some searches 
to warn me when any of the instruments you mentioned appear, since it may be a 
while before the right one shows up at the right price.

 - Compare 3 similar DUT's  with a HP 3048A and calculate the individual PN 
 using the three cornerd hat method.


That sounds like a method I'll want to learn about, since I'll necessarily be 
building up my testbench with surplus equipment of unknown condition, and the 
things I'd want to characterize initially would likely be the best oscillators 
I can get my hands on (except for the ones that no longer perform to spec, 
which I'd want to weed out). Once I have the bugs worked out of my test system, 
I could then use it to characterize other oscillators (probably far inferior to 
the Trimble/HP OCXOs) in practical applications.

 Btw. do not assume that the phase noise of a disciplined VCXO is the same as 
 the VCXO alone.
 Also keep the power supply contribution into account that can be surprisingly 
 high.

In the case of my TBolt OCXO, I'll be interested in characterizing it while 
it's in the TBolt, with its regular power supply, and under discipline, since 
that's the way I'd be using it as a frequency reference on my bench.

 And, the PN of most frequency standards is significantly lower than what you 
 can measure with any spectrum analyzer with PN measurement software (except 
 for the RS FSUP of course).

Yup, the phase noise plots I've seen of the HP and TBolt OCXOs show close-in 
phase noise very far beyond the dynamic range of any spectrum analyzers I'm 
familiar with. I wandered through the labs at work in hope of finding something 
I could use to look at the phase noise of my new toys (I'm in the GPS industry, 
and have access to some nice spectrum and network analyzers), but it looks like 
I'm on my own.


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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-20 Thread Mark J. Blair

On Aug 20, 2010, at 8:30 AM, Bob Camp wrote:
 You can make a pretty good front end (mixer / amp / lock) for under $100. 
 That will let you measure phase noise with an audio spectrum analyzer.

I am intrigued by your ideas, and I would like to subscribe to your newsletter. 
Oh, wait, I've already subscribed to your newsletter. :-)



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Re: [time-nuts] Frequency counters

2010-08-20 Thread Mark J. Blair

On Aug 20, 2010, at 10:35 AM, Stephen Farthing wrote:
 I want to find a frequency counter that will read to 1 hz precision up to a
 minimum of 30 Mhz that I can clock using the output from my Efratom 101 Rb
 frequency standard. I am quite happy to make one if there is a suitable
 design out there. Any suggestions?


I'm also beginning to look for a counter with very similar requirements. 
Studying eBay the other day, I came to the conclusion that an HP 5384A would be 
a good option, combining small size (compared to older rackmount counters), 
adequate resolution, an external reference input, and availability at fairly 
low prices. I decided that I probably don't need to hold out for one with the 
TCXO or OCXO options, since I'd generally only use it on my bench with my 
TBolt's OCXO as a reference, and it simply switches between its built-in 
reference and the external one rather than phase-locking its own reference (so 
I wouldn't be using its internal reference, and thus its performance wouldn't 
matter).


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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-20 Thread Mark J. Blair

On Aug 20, 2010, at 11:17 AM, Rick Karlquist wrote:
 On the 10811 production line, they would use Anzac AMC-123 amplifiers
 to drive a +17 dBm mixer, and then amplify the IF output with a low noise
 current amplifier like the Linear LT1028.  You can easily homebrew
 this setup.  You will need to have a DC coupled connection to the IF
 output to make a narrow PLL that drives the EFC of one of the oscillators.
 You can use a PC based audio spectrum analyzer program to look at the
 phase noise output.  You can break the PLL to get a beat note to calibrate
 the system.  The AMC-123 can also be homebrewed by reading the
 patent, which is listed on the data sheet.  No need at all to get
 a 3048, etc.

Interesting. I'm also the proud new owner of an Ettus Research USRP with a nice 
selection of RF front end boards, so maybe I could press that into service for 
spectrum analysis as long as I'm looking at things that will fall within its 
dynamic range and noise floor. I have a lot of learning to do... ;)

-- 
Mark J. Blair, NF6X n...@nf6x.net
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.





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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-20 Thread Mark J. Blair

On Aug 20, 2010, at 11:17 AM, Rick Karlquist wrote:
 On the 10811 production line, they would use Anzac AMC-123 amplifiers

How does this amplifier look for this application?

http://minicircuits.com/pdfs/ZFL-500LN.pdf

If I understand the specifications properly, the noise figure is better and it 
has higher reverse isolation and higher gain, but a lower output intercept 
point.



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Mark J. Blair, NF6X n...@nf6x.net
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.





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Re: [time-nuts] Phase noise measurement (was - no subject)

2010-08-20 Thread Mark J. Blair

On Aug 20, 2010, at 2:19 PM, Rick Karlquist wrote:
 It is good that you asked this FAQ.  Basically, what is magic
 about the AMC-123 is that it has certifiably low phase noise,
 guaranteed by design and characterization, although not specified
 by Anzac. [...] Having a low noise figure is necessary
 but not sufficient to have good phase noise.

Ah, I see. Is the AMC-123 or an equivalent still in production, or was 
homebrewing brought up as an option because it's not?


-- 
Mark J. Blair, NF6X n...@nf6x.net
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GnuPG public key available from my web page.





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Re: [time-nuts] (no subject)

2010-08-19 Thread Mark J. Blair

On Aug 19, 2010, at 4:54 PM, Bob Camp wrote:
 Yup, the original question was why a TBolt?

I just joined time-nuts today, so please forgive me if I'm beating a dead 
horse. For me, the answer to why a TBolt was it automatically calibrates 
itself against somebody else's well-maintained cesium beam oscillator that I 
didn't have to pay for, along with (presumably) low phase-noise OCXO output, 
which interests me for radio-related applications. I might have chosen a 
different kind of reference for a different application.

I haven't fabricated a good excuse to want my own rubidium standard yet, but 
I'll keep working on that. :)

-- 
Mark J. Blair, NF6X n...@nf6x.net
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.





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Re: [time-nuts] (no subject)

2010-08-19 Thread Mark J. Blair

On Aug 19, 2010, at 6:42 PM, Didier Juges wrote:
 Well, you need another reference that does not use the same principles to 
 check your first reference against.
 
 That one worked for me.

Ooooh, good one!


 Now I am working on the next one, because a man with two clocks...

...needs a third one to cancel out systematic errors?

Or how about Chicks dig guys with stable frequency and time references.

:-)


-- 
Mark J. Blair, NF6X n...@nf6x.net
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.





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Re: [time-nuts] (no subject)

2010-08-19 Thread Mark J. Blair

On Aug 19, 2010, at 7:13 PM, Bob Camp wrote:
 Hopefully they will keep GPS running long enough for me to find something to 
 compare it to.

My new GPSDO leaves me with the question of how do I measure the phase noise 
of what is by far the best oscillator I own... without buying a better one to 
compare it to. That question is what brought me to time-nuts. I'm starting to 
read some papers on oscillator characterization that are collected together in 
a technical note from NIST that a co-worker pointed me towards, but some of 
them are giving me a math-induced headache. :)


-- 
Mark J. Blair, NF6X n...@nf6x.net
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.





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