Re: [time-nuts] Need help with Lucent/Symmetricom Z3810AS

[Hal Murray]

hbre...@debitel.net said:
> I bought a Lucent/Symmetricom Z3810AS from the source on eBay and powered it
> up today for the first time. After 11 hours the RFTG-u and REF1 module is
> still showing "STBY" while the RFTG-u and REF0 module is "ON".  Is this ok
> or should the RFTG-u and REF1 module show "ON" also? 

That's the normal pattern.


> I did not try to connect a PC to get any status info because I am no
> computer wizard. In fact I have two left hands regarding computers. 

You really need that connection if you want to understand what is going on.  
Can you get a friend to help?  My setup is currently working without a 
RS422-RS232 converter.  I did have troubles a while ago with a different PC.  
I assume the problem was poor grounding.

The "No GPS" LED on my REF-1 blinks when I disconnect the antenna and goes on 
solid if I move the antenna to a crappy position (or for a while after I 
reconnect the antenna).  The same LED on the REF-0 goes on after a short 
delay - no blinking.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Need help with Lucent/Symmetricom Z3810AS

[Bob Camp]

Hi

For any sort of GPSDO to do well (not just this one) you really want an outdoor 
antenna in a good location. 
In Germany, a good location would be one that has a view of the southern sky 
from due east around
to due west. Ideally you want a view down to within 10 or 20 degrees of the 
horizon. If it’s blocked over
20% of that range, you can live with it. If it’s blocked over 60% of that 
range, you are likely to have trouble. 
Yes, a perfect location would “see” 360 degrees and view down to the horizon in 
all directions. Very few
of us have locations like that (I certainly do not). 

Almost all modern GPSDO's run external antenna. Unfortunately there is less 
standardization than you might 
hope. Each GPSDO has it’s own favorite antenna gain. In the case of the KS's, 
you want an antenna with 20 to
30 db of amplifier gain. You also want one that powers up off of +5V. You can 
find antennas that have 50 db 
amplifiers in them. You can find ones that need +12 to operate. If you have a 
long coax run, you will need more
amplifier gain to make up the coax loss. 

Distribution amplifiers can be built or they can be bought. The 10 MHz out of 
these units is nothing fancy. 
There is no reason to spend a lot of money on distribution. The last box I 
bought to do this was $30 before
shipping. It was designed as a 10 MHz 8 channel (?) distribution amp. It was 
plenty good enough to do 
what you are talking about. The internal circuits were based on logic IC’s. 

Computers are (unfortunately) an evil we must put up with today. I would 
suggest digging in the archives
for all of the details of wiring up a USB to RS-422 converter in order to talk 
to the unit. The connection info and 
the links to the software are all posted back around last Christmas. 



Only one of the two boxes will be in full operation at a time. The idea was 
that the cell station kept one of them 
in backup mode. Normally REF-1 should be “on” and REF-0 should be in standby. 
The interconnection cable 
has been the problem on the only pairs I have had issues with. Pulling it out 
and plugging it back in fixes it 
in some cases. 

Bob


> On Aug 16, 2015, at 7:01 PM, Heinz Breuer  wrote:
> 
> Hello,
> I am new to GPSDO and a new member to this list.
> 
> I bought a Lucent/Symmetricom Z3810AS from the source on eBay and powered it 
> up today for the first time. After 11 hours the RFTG-u and REF1 module is 
> still showing "STBY" while the RFTG-u and REF0 module is "ON". 
> Is this ok or should the RFTG-u and REF1 module show "ON" also?
> 
> I am in Germany and currently use an indoor GPS antenna directly behind a 
> large window facing west. Do I need to put the antenna on the roof or wait 
> even longer?
> 
> I did not try to connect a PC to get any status info because I am no computer 
> wizard. In fact I have two left hands regarding computers.
> 
> I want to use the 10MHz output as a reference for my home lab and feed 
> several frequency counters etc. I probably need to build a distribution 
> amplifier and would appreciate any hints.
> 
> vy 73 Heinz DH2FA, KM5VT
> 
> Von meinem iPhone gesendet
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Re: [time-nuts] Need help with Lucent/Symmetricom Z3810AS

[paul swed]

Heinz
I think you are working.
I have the ref1 and ref 0 crystal unit and when operational thats the way
the LEDs work.
On my unit the system locks in 15-30 minutes from a cold start.

On start up the LEDs should step.
Then the top 2 should turn on. No gps and fault
15 minutes later fault of green on
2-5 minutes later no gps off.
The ref zero aligns to the Ref1. If Ref 0 fails 1 will turn green.
Good luck
Paul
WB8TSL

On Sun, Aug 16, 2015 at 7:01 PM, Heinz Breuer  wrote:

> Hello,
> I am new to GPSDO and a new member to this list.
>
> I bought a Lucent/Symmetricom Z3810AS from the source on eBay and powered
> it up today for the first time. After 11 hours the RFTG-u and REF1 module
> is still showing "STBY" while the RFTG-u and REF0 module is "ON".
> Is this ok or should the RFTG-u and REF1 module show "ON" also?
>
> I am in Germany and currently use an indoor GPS antenna directly behind a
> large window facing west. Do I need to put the antenna on the roof or wait
> even longer?
>
> I did not try to connect a PC to get any status info because I am no
> computer wizard. In fact I have two left hands regarding computers.
>
> I want to use the 10MHz output as a reference for my home lab and feed
> several frequency counters etc. I probably need to build a distribution
> amplifier and would appreciate any hints.
>
> vy 73 Heinz DH2FA, KM5VT
>
> Von meinem iPhone gesendet
> ___
> time-nuts mailing list -- time-nuts@febo.com
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Bob Camp]

Hi

Here’s some of the “that depends” questions:

What is your stability goal? 

You talk about the NIST numbers on GPSDO’s. What level of stability are you 
after?

What is your end application? 

Is this intended as a lab standard, the reference for a radio, something else 
entirely? 

What is the destination? 

Is this heading towards a commercial venture or is it a basement project? 

What is the budget?

Do you have $200K to spend on this? Did the piggybank run dry at $100?

What is the timeline?

Does the project complete at the end of the summer, no matter what? Is it 
something that is worth another year or two of effort?

What is your background? 

Does all of the stuff we’ve been tossing around make perfect sense? (= you do
something like this for a living). Are we talking about a bunch of stuff that 
makes 
very little sense? (= you are just getting started at this sort of thing). 

Each of these twists and turns heads you off into a different set of further 
issues and 
likely some more questions. For a commercial venture, buying custom oscillators 
in 
bulk is a very normal thing to do. For a battery powered balloon carried 
reference, you
do things different than for a rack mount standard. Each of these projects 
people come up
with have its own unique drivers. 

Each of us in our replies, tries to guess what your constraints are or are not. 
In doing 
so we likely substitute our constraints for yours. The further our constraints  
diverge from 
your constraints, the further off base our advice and answers will be.

Bob



> On Aug 16, 2015, at 3:39 PM, Nick Sayer via time-nuts  
> wrote:
> 
> 
>> On Aug 16, 2015, at 12:31 PM, Tom Van Baak  wrote:
>> 
>> Anyway, to answer your question -- to measure its true performance you only 
>> need two things. 1) a phase meter (or time interval counter) that's good to 
>> 1 ns or better, and 2) a local reference standard that's maybe 10x better 
>> than the TCXO and the Adafruit GPS. Usually that means a cesium standard, or 
>> supremely qualified GPSDO, or equivalent.
> 
> I have a frequency counter, but it’s not a phase meter. I have a scope, but I 
> assume that trying to use a ruler with scope traces isn’t the textbook way of 
> doing that. :D
> 
> I have considered in the past buying a used rubidium standard off eBay, but 
> have hesitated because I don’t know how much life there is left in the tube, 
> and I just have to take it on faith that it’s stable and accurate. I have 
> somewhat more faith in the GPS PPS, but clearly that has limits.
> 
>> 
>> A number of us here on the time-nuts list have such equipment at home. And 
>> unlike professional labs, we will do it for free/fun if you loan the GPSDO 
>> for a week.
> 
> I will happily *give* one to someone if they would be willing to help a 
> relative newbie with this stuff.
> 
> Just one though. They’re kind of expensive to build. :D
> 
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Nick Sayer via time-nuts]

> On Aug 16, 2015, at 1:53 PM, Graham / KE9H  wrote:
> 
> Nick:
> 
> From your description, it sounds like you have a frequency locked loop with
> a maximum frequency sensitivity of 1 ppb, as opposed to a phase locked loop.

Yes. I am leveraging the capabilities of the microcontroller as much as I can. 
It has a 16 bit timer that is clocked from the system clock (the 10 MHz 
oscillator). The timer has “input capture” capability - the rising PPS edge 
copies the clock reading into a holding register and triggers an interrupt. The 
only extra hardware required is the 16 bit DAC and its output buffer. That 
circuit is largely copied from a Connor Winfield application note.

Since people have brought it up, I’ve considered how I would do a PLL system. 
I’d probably use something like an ATTiny25 to do a simple 
divide-by-ten-million in software. That, and the PPS signal would go into a 
phase comparator that would (in my mind) have some sort of interface to the 
controller to allow the controller to get a high granularity view of the phase 
angle between the two. It would then apply feedback with the DAC and (as now) 
blink the LOCK LED to indicate quality. The DAC would probably need an upgrade 
as well to have more feedback granularity. All of that adds to the cost (as 
does my low production volume).

> 
> At the end of the 100 second count period, do you start over with a counter
> set to zero, or do you carry forward any error from the previous period?

For the purpose of feedback to the oscillator, only the 100 second error count 
is used. The adjustment granularity is on the order of 370 ppt or so, so I’m 
not sure there much more “there” there.

For the purpose of user feedback (the LOCK LED has four different states 
indicating no lock: >50 ppb, “good”: 50-5 ppb, “better”: 5ppb-1ppb and “best”: 
<1 ppb), there is a rolling window of ten 100 second samples that are 
aggregated for a 1000 second window. So when the “best” blink is happening, it 
means that the error over the past 1000 seconds is < 10 counts.

> 
> --- Graham
> 
> ==
> 
> 
> 
> 
> On Sun, Aug 16, 2015 at 2:31 PM, Tom Van Baak  wrote:
> 
>> Hi Nick,
>> 
>> Nice project. Thanks for sharing.
>> 
>> I was hoping someone would someday use a cheap Sparkfun / Parallax /
>> Adafruit GPS to make a low-cost GPSDO. Mostly what people on this list do
>> is go to the extreme of using serious GPS timing receivers (such as Oncore
>> M12+T, or ublox-5T or 6T or 8T) but those require significant amounts of
>> configuration, tuning, survey, etc. to meet ultimate performance levels.
>> 
>> The good thing about using a cheap hobbyist-grade 3D GPS/1PPS receiver is
>> that they work anywhere, without fiddling or survey, within seconds of
>> power-on. Ok, you lose a few ns of precision compared to serious receivers
>> -- but for a TCXO that doesn't matter.
>> 
>> Anyway, to answer your question -- to measure its true performance you
>> only need two things. 1) a phase meter (or time interval counter) that's
>> good to 1 ns or better, and 2) a local reference standard that's maybe 10x
>> better than the TCXO and the Adafruit GPS. Usually that means a cesium
>> standard, or supremely qualified GPSDO, or equivalent.
>> 
>> A number of us here on the time-nuts list have such equipment at home. And
>> unlike professional labs, we will do it for free/fun if you loan the GPSDO
>> for a week.
>> 
>> If you want to play with raw timing data from an Adafruit GPS board see
>> file gps-mtk3339.txt.gz under http://www.leapsecond.com/pages/gpsdo-sim/
>> and then use TimeLab for phase, frequency, and Allan deviation analysis (
>> http://www.ke5fx.com/timelab/readme.htm).
>> 
>> /tvb
>> 
>> - Original Message -
>> From: "Nick Sayer via time-nuts" 
>> To: 
>> Sent: Sunday, August 16, 2015 11:47 AM
>> Subject: [time-nuts] I've designed a GPSDO, but how "good" is it?
>> 
>> 
>> I’ve designed and make and sell a GPSDO on Tindie (
>> https://hackaday.io/project/6872-gps-disciplined-tcxo). It’s brand new -
>> I’ve sold a handful of them so far. So as to make this post not *entirely*
>> self-serving, what I would like is some further guidance on how I can
>> better characterize its performance.
>> 
>> The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module
>> - a PA6H). The manufacturer claims an accuracy of ±10 ns, but that's
>> accuracy relative to the true start of the GPS second. They don’t make any
>> claim for stability.
>> 
>> The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term
>> (though they don’t say how short that term is) stability of 1 ppb. The
>> absolute accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and
>> the control voltage is steered by GPS feedback.
>> 
>> The feedback loop takes samples over a 100 second period. That gives me an
>> error sample with a granularity of 1 ppb. I keep a rolling sample window of
>> 10 samples to get an error count over 1000 seconds. I've kept track of both
>> of these val

Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Bob Camp]

Hi

The “wear out” on a Rb is not the same as wear out on a 
Cesium standard. In a Cs, you have a finite number if atoms
loaded in at the factory. When those atoms all travel down the 
tube, it’s dead. In an Rb, the atoms don’t go anywhere. There is
no built in “end of life”. They mostly die from MTBF sorts of things 
due to complexity and high temperatures, There are HP Rb’s 
built many decades ago still running on their original cells.

Bob



> On Aug 16, 2015, at 6:10 PM, Attila Kinali  wrote:
> 
> On Sun, 16 Aug 2015 12:39:19 -0700
> Nick Sayer via time-nuts  wrote:
> 
>> I have considered in the past buying a used rubidium standard off eBay,
>> but have hesitated because I don’t know how much life there is left in
>> the tube, and I just have to take it on faith that it’s stable and accurate.
>> I have somewhat more faith in the GPS PPS, but clearly that has limits.
> 
> 
> Don't worry about that.
> The cheap FE-5680 that have been around for a while have a couple of
> years left at least. And even if they go out, you can revive them
> with a hot air gun.
> 
>   Attila Kinali
> 
> -- 
> I must not become metastable. 
> Metastability is the mind-killer.
> Metastability is the little-death that brings total obliteration.
> I will face my metastability. 
> I will permit it to pass over me and through me. 
> And when it has gone past I will turn the inner eye to see its path. 
> Where the metastability has gone there will be nothing. Only I will remain.
> 
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Bob Camp]

Hi

Let’s say you want to measure a GPSDO over it’s entire range. The only 
practical approaches
are comparison based. You either need a fancy cesium standard / hydrogen maser 
or you compare
to another GPSDO. If you are making GPSDO’s having more than one around is a 
practical answer.
To take common mode issues out of the setup, you don’t really want to compare 
two identical GPSDO’s.
They are a lot cheaper than an atomic clock, you buy several.

Next you need something to measure with. Ideally you want a floor around 
1x10^-13 for a 1 second 
single shot measurement. No fair taking a million 1 second measurements at 
1x10^-10 and averaging
to get 1x10^-13. You can buy fine pieces of test gear that will do a single 
shot below 1x10^-13. The 
TimePod is one example. There are many others. I know of no “low cost” off the 
shelf gear that will get you there.

The 1x10^-13 is a bit arbitrary. Since you will likely improve resolution as 
tau increases, you could
simply ignore short tau testing. A 1x10^-9 (1 ns) single shot counter will get 
you to 1x10^-13 at 1,000
seconds. That’s a bit long of a wait. You want > 10 readings and prefer > 100 
for characterizing this kind 
of thing. A minimum run time of a day is pretty slow. It also makes it quite 
hard to figure out what’s going
on with things like filter tuning.

The most practical answer to the measurement question is either a single mixer 
or a dual (or triple or
quad..) down conversion system. You can build one that will get you at least to 
the 1-2x10^-12 at one second 
level without a lot of crazy work. You can get to 10X better than that with a 
bit of care. With a single mixer
you will need an offset reference source for comparison. With a double or 
higher, you can directly compare two
devices on the same frequency.

If this sounds a bit crazy - welcome to the modern world. Hardware development 
takes a back seat to
firmware and testing. True both on cost and time.

So what does the setup look like:

Two or more eBay GPSDO models that have fairly well documented performance.

Likely at least two of one of the models so you can compare against published 
data.

Some pretty good buffering and splitting to pass the signals around.

A couple of older counters and GPIB to talk to them. (LOTS of alternatives here)

An OCXO as the heterodyne “offset” for your mixers.

Distribution, splitting, amplification for the OCXO (takes care of nasty cross 
talk issues)

A mixer for each device you will test plus a limiter / amplifier. (each goes to 
it’s own counter)

Yes, there is some stuff there. It’s not a lot of stuff. Commercial gear will 
be in the > $5K 
(and maybe >> $5K) range. Four 5334’s or 5335’s plus three or four GPSDO’s 
should be under 
$1K if you shop a bit.

==

So how about hiring the job out? Well a run is likely to take a week or two of 
equipment time. 
That’s about 300 hours. The tradeoff cost on the first run is $3 per hour. 
That’s a lot if gear tied 
up for $3 ….Let’s say you find a lab and indeed it’s only $1,000. Back comes 
the report. Here
is what your device looks like over that period.

Trust me on this, the result will not make you happy. The first real test if 
anything like this 
never is great, Next question - what’s wrong? You make some guesses. You change 
some
things. You get it all boxed back up. Back to the out side test. Crunch, out 
goes another $1K.

How many passes to expect? A year or so of testing is not uncommon on this sort 
of thing.
Even if you get one pass of testing free, you will have lots of passes after 
that …

You can’t afford to pay for commercial testing. It’s far more likely to be $30 
a machine hour than $3.If 
you are serious about designing one of these beasts, a lab setup is essential. 

Bob



> On Aug 16, 2015, at 4:00 PM, Charles Steinmetz  wrote:
> 
> Nick wrote:
> 
>> The GPS reference is a 1 pps signal   * * *
>> 
>> The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term 
>> (though they don't say how short that term is) stability of 1 ppb.   * * *
>> 
>> The feedback loop takes samples over a 100 second period. That gives me an 
>> error sample with a granularity of 1 ppb. I keep a rolling sample window of 
>> 10 samples to get an error count over 1000 seconds.
> 
> The limitations are fundamental.  The GPS signal has stability in the e-13 
> range, BUT only when averaged for 10,000 seconds or more (tau greater than or 
> equal to 10,000 seconds).  It is actually quite noisy over short periods -- 
> it can be as bad as e-7 over one second.  So, a GPSDO relies on its local 
> oscillator for stability for periods shorter than 1000 seconds or so.  A good 
> OCXO can provide stability in the e-10 range at tau in the 1 second to 100 
> second range, but even a very good TCXO cannot do that well.
> 
> The point of a GPSDO is to rely on the stability of the local oscillator at 
> short tau, where it is better than the GPS stability, and to cross over to 
> the greater GPS stabilit

Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Nick Sayer via time-nuts]

> On Aug 16, 2015, at 2:27 PM, Attila Kinali  wrote:
> 
> On Sun, 16 Aug 2015 11:47:23 -0700
> Nick Sayer via time-nuts  wrote:
> 
>> I’ve designed and make and sell a GPSDO on Tindie 
>> (https://hackaday.io/ project/6872-gps-disciplined-tcxo). It’s brand new - 
>> I’ve sold a handful of them so far. So as to make this post not *entirely* 
>> self-serving, what I would like is some further guidance on how I can better 
>> characterize its performance.
>> 
>> The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module - 
>> a PA6H). The manufacturer claims an accuracy of ±10 ns, but that's accuracy 
>> relative to the true start of the GPS second. They don’t make any claim for 
>> stability.
> 
> And under the assumption that you have a high gain antenna high up on a roof
> with negligible multipath. As reference, have a look at [1], that's a
> LEA6-T against a Rb vapor cell, with a antenna on the building roof.
> And of course, the LEA6-T in position hold mode.

Not so much. I have one of these: https://www.adafruit.com/products/960, and 
the board comes standard with a U.FL jack that you can use with a pigtail to 
connect whatever you like.

> 
> Said Jackson once reportet that he got a PPS jitter of 1us by placing
> a patch antenna in a window. He got something much lower (sorry, don't
> remember the number) after averaging the position for a week.
> 
> 
> Given that you have only a position gps receiver, and not a timing module.
> Which on top of it is optimized for small size with an integrated antenna,
> i'd say that those 10ns are overly optimistic.
> 
>> The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term 
>> (though they don’t say how short that term is) stability of 1 ppb. The 
>> absolute accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and 
>> the control voltage is steered by GPS feedback.
> 
> Having a look at the datasheet, i'd say that 1e-9 at 1s.
> Which sounds reasonable as a manufacturer spec (i.e. as the maximum
> expected instability at 1s)
> 
> 
>> 
>> The feedback loop takes samples over a 100 second period. That gives me
>> an error sample with a granularity of 1 ppb.
> 
> I guess you are running the timer at 10MHz then?

Yes. When I began, I started with a 20 MHz design, but discovered (thankfully 
before I got too deep) that the ATMel controllers won’t clock that fast at 3.3 
volts.

> 
>> I keep a rolling sample window
>> of 10 samples to get an error count over 1000 seconds. I've kept track of 
>> both of these values for extended periods (days) as well as logging the DAC 
>> value (the number that's proportional to the control voltage). The 1000 
>> second sample window error averages zero, and it almost never exceeds ±7 
>> (every once in a while if I physically move it, it will show a momentary 
>> error glitch, but that shows up in the short term feedback sampling too). 
>> The 100 second samples are almost all 0 or ±1, with an occasional ±2 showing 
>> > up. As I said before, if I bonk the oscillator, it may briefly show a ±6 
>> or 
>> so for one sample.
> 
> This sounds that your somewhere the resolution is too low. 
> From what you have written above, i'd say that the TIC resolution is at
> least borderline, if not too low. For the DAC: You have a 16bit DAC, with
> Vref at 3.3V and a tuning range of >+/-10ppm between 0.3 and 3.0V.. that
> makes a step size of >0.373ppb per LSB. With the manufacturer spec of the
> VCTCXO of <1ppb@1s I would say your DAC resolution is too low as well.
> 
> The +/-6 excursions are most likely from shock to the oscillator.

Yeah, I figured that. I try and avoid doing that as much as possible. :) Since 
the goal is a lab standard, I think it’s ok to assume it’s not going to move.

> See [2] for details on that.
> 
>> 
>> If I pit two of them against each other on a scope and take a time lapse
>> video (http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they
>> stay mostly locked with occasional periods of drift. I sort of assume that
>> that represents periods where the two GPS receivers disagree as they decide
>> differently how to select among the available satellites.
> 
> What is the time period of that video?

1 hour.

> 
> If I counted correctly, you have a maximum offset of 350ns. For GPSDOs
> that are close to each other, that's a quite considerable shift of phase.
> Are you sure your software implements a phase locked loop and not a
> frequency locked loop?

The firmware is at: https://github.com/nsayer/GPS-disciplined-OXCO

I’d be hard pressed to see how it’s anything other than an FLL. There’s no 
phase comparator. I’m counting how many system clock cycles happen between PPS 
rising edges. That’s it.

> Or is your antenna position extremely bad?

It’s hard for me to characterize your expectations, however when I made those 
videos only one of the units had the benefit of the external antenna, as I only 
(at the moment) have one. And even if I had more than one, it doesn’t

Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Attila Kinali]

On Sun, 16 Aug 2015 23:27:43 +0200
Attila Kinali  wrote:

> > I've been saying out loud that the oscillator is ±1 ppb from GPS over the
> > 1000 second window. I know of Allan variance, but I don't have anything else
> > handy I can use for comparison. I also can't really afford to send one off
> > for testing to a proper lab. 
> 
> With not having any other reference, you can use the EFC voltage
> and its relation to frequency as a guestimator for the ADEV. But
> be aware that the EFC is not 100% linear and the instability of your
> voltage reference etc pp affects this value as well. There was some
> discussion about this technique a couple of years ago (IIRC 2008)
> on this mailinglist. But i cannot find at the moment... it had some
> weird name too... Maybe someone with a better long term memory can
> chip in on that.

Found it. It is called "tight pll" or "tpll", you can find a summary here:
http://www.ke5fx.com/tpll.htm

Attila Kinali

-- 
I must not become metastable. 
Metastability is the mind-killer.
Metastability is the little-death that brings total obliteration.
I will face my metastability. 
I will permit it to pass over me and through me. 
And when it has gone past I will turn the inner eye to see its path. 
Where the metastability has gone there will be nothing. Only I will remain.

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[time-nuts] Need help with Lucent/Symmetricom Z3810AS

[Heinz Breuer]

Hello,
I am new to GPSDO and a new member to this list.

I bought a Lucent/Symmetricom Z3810AS from the source on eBay and powered it up 
today for the first time. After 11 hours the RFTG-u and REF1 module is still 
showing "STBY" while the RFTG-u and REF0 module is "ON". 
Is this ok or should the RFTG-u and REF1 module show "ON" also?

I am in Germany and currently use an indoor GPS antenna directly behind a large 
window facing west. Do I need to put the antenna on the roof or wait even 
longer?

I did not try to connect a PC to get any status info because I am no computer 
wizard. In fact I have two left hands regarding computers.

I want to use the 10MHz output as a reference for my home lab and feed several 
frequency counters etc. I probably need to build a distribution amplifier and 
would appreciate any hints.

vy 73 Heinz DH2FA, KM5VT

Von meinem iPhone gesendet
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Re: [time-nuts] Trimble GPS board

[M. George]

Sorry, one more eBay link using this Trimble unit:

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/18173438?hash=item2a52ccb37e
​Is that the bg7tbl version?  Not sure what the serial connection gives you
unless it's al'a BG7TBL?

mg​



On Sun, Aug 16, 2015 at 3:36 PM, M. George 
wrote:

> Hi, I poked around and found the EEVblog thread below... BG7TBL is using
> this board in one of his GPSDO units he sells on eBay.
>
> Look through the whole thread, you will see pictures of the GPSDO that is
> using this board / OCXO:
>
> http://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/
>
> And yet another eBay seller that is offering this board, I have seen this
> quite a bit in the past, but at $99 I didn't get excited:
>
>
> http://www.ebay.com/itm/like/301124758583?item=301124758583&vectorid=229466&rmvSB=true
>
> And another $119 complete with the patch coax to SMA connectors and it
> shows the 6v power connection input:
>
>
> http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/18173438?hash=item2a52ccb37e
> mg NG7M
>
> On Sun, Aug 16, 2015 at 1:25 PM, Bob Camp  wrote:
>
>> Hi
>>
>> I think you will find that on the part you are looking at:
>>
>> TPN = Trimble Part Number
>> 57964-15 = Trimble’s part number on the module
>> SEC CODE = probably more relevant to the module that the OCXO info
>>
>> Date Code (on OCXO) 0826 = it was made sometime around the middle of 2008
>>
>> One would *guess* that it is a more modern version of the TBolt.
>>
>> Bob
>>
>>
>> > On Aug 16, 2015, at 10:52 AM, Bob Benward  wrote:
>> >
>> > Hi all,
>> >
>> > Does anyone have any information or experience with this small Trimble
>> > GPSDO?  There doesn't seem to be any associated model number other than
>> the
>> > model of the OCXO (63090).  I am looking for software, command codes, or
>> > hookup schematics, can anyone help?
>> >
>> >
>> >
>> > http://www.ebay.com/itm/141734507722?_trksid=p2057872.m2749.l2649
>> > <
>> http://www.ebay.com/itm/141734507722?_trksid=p2057872.m2749.l2649&ssPageNam
>> > e=STRK%3AMEBIDX%3AIT> &ssPageName=STRK%3AMEBIDX%3AIT
>> >
>> >
>> >
>> > Thanks,
>> >
>> > Bob
>> >
>> > ___
>> > time-nuts mailing list -- time-nuts@febo.com
>> > To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> > and follow the instructions there.
>>
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
>
>
> --
> M. George
>



-- 
M. George
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[time-nuts] Heol N024 GPS for TS-2100 Failure

[Gerhard Wittreich]

After 2-3 months of stable operation I noticed today that the "Tracking"
and "Locked" lights on my upgraded (w/ Heol Design N024 GPS board) TS-2100
were not lit.  I tried to access the GPS board but got a "GPS Engine Busy"
and "*** err *** handshake timeout" error.  Everything else appears to be
functioning.  Basic troubleshooting (ie. restart and reseating the board)
have not resolved the issue.  It looks like a GPS board failure.  I've
contact Heol Design this evening and am waiting for a reply.

I assume no one else has seen this problem.  I look forward to how they
respond.

--Gerhard R Wittreich, P.E.
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Re: [time-nuts] Trimble GPS board

[M. George]

Hi, I poked around and found the EEVblog thread below... BG7TBL is using
this board in one of his GPSDO units he sells on eBay.

Look through the whole thread, you will see pictures of the GPSDO that is
using this board / OCXO:

http://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/

And yet another eBay seller that is offering this board, I have seen this
quite a bit in the past, but at $99 I didn't get excited:

http://www.ebay.com/itm/like/301124758583?item=301124758583&vectorid=229466&rmvSB=true

And another $119 complete with the patch coax to SMA connectors and it
shows the 6v power connection input:

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/18173438?hash=item2a52ccb37e
mg NG7M

On Sun, Aug 16, 2015 at 1:25 PM, Bob Camp  wrote:

> Hi
>
> I think you will find that on the part you are looking at:
>
> TPN = Trimble Part Number
> 57964-15 = Trimble’s part number on the module
> SEC CODE = probably more relevant to the module that the OCXO info
>
> Date Code (on OCXO) 0826 = it was made sometime around the middle of 2008
>
> One would *guess* that it is a more modern version of the TBolt.
>
> Bob
>
>
> > On Aug 16, 2015, at 10:52 AM, Bob Benward  wrote:
> >
> > Hi all,
> >
> > Does anyone have any information or experience with this small Trimble
> > GPSDO?  There doesn't seem to be any associated model number other than
> the
> > model of the OCXO (63090).  I am looking for software, command codes, or
> > hookup schematics, can anyone help?
> >
> >
> >
> > http://www.ebay.com/itm/141734507722?_trksid=p2057872.m2749.l2649
> > <
> http://www.ebay.com/itm/141734507722?_trksid=p2057872.m2749.l2649&ssPageNam
> > e=STRK%3AMEBIDX%3AIT> &ssPageName=STRK%3AMEBIDX%3AIT
> >
> >
> >
> > Thanks,
> >
> > Bob
> >
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 
M. George
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Charles Steinmetz]

Nick wrote:


The GPS reference is a 1 pps signal   * * *

The oscillator itself (Connor Winfield DOT050V 10 MHz) has a 
short-term (though they don't say how short that term is) stability 
of 1 ppb.   * * *


The feedback loop takes samples over a 100 second period. That gives 
me an error sample with a granularity of 1 ppb. I keep a rolling 
sample window of 10 samples to get an error count over 1000 seconds.


The limitations are fundamental.  The GPS signal has stability in the 
e-13 range, BUT only when averaged for 10,000 seconds or more (tau 
greater than or equal to 10,000 seconds).  It is actually quite noisy 
over short periods -- it can be as bad as e-7 over one second.  So, a 
GPSDO relies on its local oscillator for stability for periods 
shorter than 1000 seconds or so.  A good OCXO can provide stability 
in the e-10 range at tau in the 1 second to 100 second range, but 
even a very good TCXO cannot do that well.


The point of a GPSDO is to rely on the stability of the local 
oscillator at short tau, where it is better than the GPS stability, 
and to cross over to the greater GPS stability at longer tau by 
disciplining the LO to GPS.  You have chosen a local oscillator with 
not very good stability at short tau, so your stability at short tau 
will not be very good (compared to well-designed GPSDOs using OCXOs) 
-- likely 3 to 4 orders of magnitude worse.  Additionally, your 
disciplining algorithm does not sound as if it gets the most out of 
the parts you are using.


In order to measure the stability of your GPSDO, you will need a time 
interval counter (preferably), or a frequency counter, with a 
resolution at least 1nS, preferably 20pS or so.  You can use another 
one of your GPSDOs as a "reference" and attribute half the rms error 
to each one -- but preferably you would use a reference at least 10x 
better than the DUT at all tau of interest.  You will collect data 
for long enough to get stability numbers for the longest tau you care 
about (at least 30 minutes), then use a program like TimeLab to 
calculate the stability from the raw data.


Sorry to say, you can do much better buying one of the Lucent or 
Trimble boxes for $150 on ebay.


Best regards,

Charles



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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Attila Kinali]

On Sun, 16 Aug 2015 11:47:23 -0700
Nick Sayer via time-nuts  wrote:

> I’ve designed and make and sell a GPSDO on Tindie 
> (https://hackaday.io/ project/6872-gps-disciplined-tcxo). It’s brand new - 
> I’ve sold a handful of them so far. So as to make this post not *entirely* 
> self-serving, what I would like is some further guidance on how I can better 
> characterize its performance.
> 
> The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module - 
> a PA6H). The manufacturer claims an accuracy of ±10 ns, but that's accuracy 
> relative to the true start of the GPS second. They don’t make any claim for 
> stability.

And under the assumption that you have a high gain antenna high up on a roof
with negligible multipath. As reference, have a look at [1], that's a
LEA6-T against a Rb vapor cell, with a antenna on the building roof.
And of course, the LEA6-T in position hold mode.

Said Jackson once reportet that he got a PPS jitter of 1us by placing
a patch antenna in a window. He got something much lower (sorry, don't
remember the number) after averaging the position for a week.


Given that you have only a position gps receiver, and not a timing module.
Which on top of it is optimized for small size with an integrated antenna,
i'd say that those 10ns are overly optimistic.

> The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term 
> (though they don’t say how short that term is) stability of 1 ppb. The 
> absolute accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and 
> the control voltage is steered by GPS feedback.

Having a look at the datasheet, i'd say that 1e-9 at 1s.
Which sounds reasonable as a manufacturer spec (i.e. as the maximum
expected instability at 1s)


> 
> The feedback loop takes samples over a 100 second period. That gives me
> an error sample with a granularity of 1 ppb.

I guess you are running the timer at 10MHz then?

>  I keep a rolling sample window
> of 10 samples to get an error count over 1000 seconds. I've kept track of 
> both of these values for extended periods (days) as well as logging the DAC 
> value (the number that's proportional to the control voltage). The 1000 
> second sample window error averages zero, and it almost never exceeds ±7 
> (every once in a while if I physically move it, it will show a momentary 
> error glitch, but that shows up in the short term feedback sampling too). 
> The 100 second samples are almost all 0 or ±1, with an occasional ±2 showing 
> > up. As I said before, if I bonk the oscillator, it may briefly show a ±6 or 
> so for one sample.

This sounds that your somewhere the resolution is too low. 
>From what you have written above, i'd say that the TIC resolution is at
least borderline, if not too low. For the DAC: You have a 16bit DAC, with
Vref at 3.3V and a tuning range of >+/-10ppm between 0.3 and 3.0V.. that
makes a step size of >0.373ppb per LSB. With the manufacturer spec of the
VCTCXO of <1ppb@1s I would say your DAC resolution is too low as well.

The +/-6 excursions are most likely from shock to the oscillator.
See [2] for details on that.

> 
> If I pit two of them against each other on a scope and take a time lapse
> video (http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they
> stay mostly locked with occasional periods of drift. I sort of assume that
> that represents periods where the two GPS receivers disagree as they decide
> differently how to select among the available satellites.

What is the time period of that video?

If I counted correctly, you have a maximum offset of 350ns. For GPSDOs
that are close to each other, that's a quite considerable shift of phase.
Are you sure your software implements a phase locked loop and not a
frequency locked loop? Or is your antenna position extremely bad?

> I've been saying out loud that the oscillator is ±1 ppb from GPS over the
> 1000 second window. I know of Allan variance, but I don't have anything else
> handy I can use for comparison. I also can't really afford to send one off
> for testing to a proper lab. 

With not having any other reference, you can use the EFC voltage
and its relation to frequency as a guestimator for the ADEV. But
be aware that the EFC is not 100% linear and the instability of your
voltage reference etc pp affects this value as well. There was some
discussion about this technique a couple of years ago (IIRC 2008)
on this mailinglist. But i cannot find at the moment... it had some
weird name too... Maybe someone with a better long term memory can
chip in on that.

> In looking at 
> http://tf.nist.gov/general/pdf/2297.pdf, it suggests that my results are 
> relatively poor compared to what a GPSDO can achieve (more like 10^-12 
> rather than 10^-9), but I assume that they’re able to use a higher frequency 
> GPS reference than just 1 PPS (and they’re a lot pricier).

Uhmm.. these GPSDOs are in an other league than yours.

You have a position GPS receiver with an antenna, not only in a poor
po

Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Jim Harman]

On Sun, Aug 16, 2015 at 3:31 PM, Tom Van Baak  wrote:

> I was hoping someone would someday use a cheap Sparkfun / Parallax /
> Adafruit GPS to make a low-cost GPSDO.


I have made such a device using the Adafruit module and an Arduino
processor. The design is based on the one posted here by Lars Walenius last
year. My design constraints were basically:
-- no surface mount components that I have to solder myself
-- no custom PC boards
-- no built-in display, runs stand-alone or with a PC as a monitor

My oscillator is a 10 MHz C-Mac STP-2322 from the auction site.

Like Nick, I do not have an independent reference to compare it to, but it
is set up with a laptop as a monitor so I can plot the TIC output in real
time.

I have attached a screenshot that shows the TIC variation over 24
hours.This is with a filter time constant of 2048 seconds. The black line
at the center is the raw TIC value, sampled every 86 seconds, and the red
line is a smoothed version of that. The vertical scale is approx. 100 ns
per division (range is 300-700). As you can see, TIC variation is typically
about +/- 40 ns. The longer term variations are very repeatable from day to
day, probably due to the periodicity of the GPS constellation.

I am using Adafruit's external antenna located in my attic with 10m of
extra cable. As often observed here, the variation is much worse if I have
a poor antenna location. It would probably be better if my antenna was up
high and outdoors.

The blue line at the bottom is the value being sent to the DAC and the
green line at the top is the ambient temperature


--Jim Harman
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Attila Kinali]

On Sun, 16 Aug 2015 12:39:19 -0700
Nick Sayer via time-nuts  wrote:

> I have considered in the past buying a used rubidium standard off eBay,
> but have hesitated because I don’t know how much life there is left in
> the tube, and I just have to take it on faith that it’s stable and accurate.
> I have somewhat more faith in the GPS PPS, but clearly that has limits.


Don't worry about that.
The cheap FE-5680 that have been around for a while have a couple of
years left at least. And even if they go out, you can revive them
with a hot air gun.

Attila Kinali

-- 
I must not become metastable. 
Metastability is the mind-killer.
Metastability is the little-death that brings total obliteration.
I will face my metastability. 
I will permit it to pass over me and through me. 
And when it has gone past I will turn the inner eye to see its path. 
Where the metastability has gone there will be nothing. Only I will remain.

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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Magnus Danielson]

Hi,

I warmly recommend people to play around with Tom's GPSDO-SIM tool. It's 
a quick way to get some important learnings about what knobs do what on 
the response.


Cheers,
Magnus

On 08/16/2015 09:31 PM, Tom Van Baak wrote:

Hi Nick,

Nice project. Thanks for sharing.

I was hoping someone would someday use a cheap Sparkfun / Parallax / Adafruit 
GPS to make a low-cost GPSDO. Mostly what people on this list do is go to the 
extreme of using serious GPS timing receivers (such as Oncore M12+T, or 
ublox-5T or 6T or 8T) but those require significant amounts of configuration, 
tuning, survey, etc. to meet ultimate performance levels.

The good thing about using a cheap hobbyist-grade 3D GPS/1PPS receiver is that 
they work anywhere, without fiddling or survey, within seconds of power-on. Ok, 
you lose a few ns of precision compared to serious receivers -- but for a TCXO 
that doesn't matter.

Anyway, to answer your question -- to measure its true performance you only 
need two things. 1) a phase meter (or time interval counter) that's good to 1 
ns or better, and 2) a local reference standard that's maybe 10x better than 
the TCXO and the Adafruit GPS. Usually that means a cesium standard, or 
supremely qualified GPSDO, or equivalent.

A number of us here on the time-nuts list have such equipment at home. And 
unlike professional labs, we will do it for free/fun if you loan the GPSDO for 
a week.

If you want to play with raw timing data from an Adafruit GPS board see file 
gps-mtk3339.txt.gz under http://www.leapsecond.com/pages/gpsdo-sim/ and then 
use TimeLab for phase, frequency, and Allan deviation analysis 
(http://www.ke5fx.com/timelab/readme.htm).

/tvb

- Original Message -
From: "Nick Sayer via time-nuts" 
To: 
Sent: Sunday, August 16, 2015 11:47 AM
Subject: [time-nuts] I've designed a GPSDO, but how "good" is it?


I’ve designed and make and sell a GPSDO on Tindie 
(https://hackaday.io/project/6872-gps-disciplined-tcxo). It’s brand new - I’ve 
sold a handful of them so far. So as to make this post not *entirely* 
self-serving, what I would like is some further guidance on how I can better 
characterize its performance.

The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module - a 
PA6H). The manufacturer claims an accuracy of ±10 ns, but that's accuracy 
relative to the true start of the GPS second. They don’t make any claim for 
stability.

The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term (though 
they don’t say how short that term is) stability of 1 ppb. The absolute 
accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and the control 
voltage is steered by GPS feedback.

The feedback loop takes samples over a 100 second period. That gives me an 
error sample with a granularity of 1 ppb. I keep a rolling sample window of 10 
samples to get an error count over 1000 seconds. I've kept track of both of 
these values for extended periods (days) as well as logging the DAC value (the 
number that's proportional to the control voltage). The 1000 second sample 
window error averages zero, and it almost never exceeds ±7 (every once in a 
while if I physically move it, it will show a momentary error glitch, but that 
shows up in the short term feedback sampling too). The 100 second samples are 
almost all 0 or ±1, with an occasional ±2 showing up. As I said before, if I 
bonk the oscillator, it may briefly show a ±6 or so for one sample.

If I pit two of them against each other on a scope and take a time lapse video 
(http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they stay mostly 
locked with occasional periods of drift. I sort of assume that that represents 
periods where the two GPS receivers disagree as they decide differently how to 
select among the available satellites.

I've been saying out loud that the oscillator is ±1 ppb from GPS over the 1000 
second window. I know of Allan variance, but I don't have anything else handy I 
can use for comparison. I also can't really afford to send one off for testing 
to a proper lab. In looking at http://tf.nist.gov/general/pdf/2297.pdf, it 
suggests that my results are relatively poor compared to what a GPSDO can 
achieve (more like 10^-12 rather than 10^-9), but I assume that they’re able to 
use a higher frequency GPS reference than just 1 PPS (and they’re a lot 
pricier).

What else can I do to try and characterize the performance? If mine is 
performing far more poorly than the same price ($175) can buy elsewhere, then 
what am I doing wrong?

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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Tim Shoppa]

Nick, professional GPSDO's achieve precision much less than one 10MHz
count, by doing sub-nanosecond level time interval measurements between GPS
PPS and the OCXO-divided-by-10M-PPS. During initial lock there is some
software smarts to reset the divide-by-10M chain at the right point so the
initial lock is a bit more like a frequency lock rather than a phase lock -
these smarts also kick in if there is a substantial disturbance to phase to
be resolved (that substantial difference probably doesn't require a real
EFC correction but instead is some kind of glitch ridden over by going to
frequency lock.)

Google things like "z3801a tic" (tic = time interval converter) to see past
discussions about the state of the art a few decades ago.

Tim N3QE

On Sun, Aug 16, 2015 at 2:47 PM, Nick Sayer via time-nuts <
time-nuts@febo.com> wrote:

> I’ve designed and make and sell a GPSDO on Tindie (
> https://hackaday.io/project/6872-gps-disciplined-tcxo). It’s brand new -
> I’ve sold a handful of them so far. So as to make this post not *entirely*
> self-serving, what I would like is some further guidance on how I can
> better characterize its performance.
>
> The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module
> - a PA6H). The manufacturer claims an accuracy of ±10 ns, but that's
> accuracy relative to the true start of the GPS second. They don’t make any
> claim for stability.
>
> The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term
> (though they don’t say how short that term is) stability of 1 ppb. The
> absolute accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and
> the control voltage is steered by GPS feedback.
>
> The feedback loop takes samples over a 100 second period. That gives me an
> error sample with a granularity of 1 ppb. I keep a rolling sample window of
> 10 samples to get an error count over 1000 seconds. I've kept track of both
> of these values for extended periods (days) as well as logging the DAC
> value (the number that's proportional to the control voltage). The 1000
> second sample window error averages zero, and it almost never exceeds ±7
> (every once in a while if I physically move it, it will show a momentary
> error glitch, but that shows up in the short term feedback sampling too).
> The 100 second samples are almost all 0 or ±1, with an occasional ±2
> showing up. As I said before, if I bonk the oscillator, it may briefly show
> a ±6 or so for one sample.
>
> If I pit two of them against each other on a scope and take a time lapse
> video (http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they
> stay mostly locked with occasional periods of drift. I sort of assume that
> that represents periods where the two GPS receivers disagree as they decide
> differently how to select among the available satellites.
>
> I've been saying out loud that the oscillator is ±1 ppb from GPS over the
> 1000 second window. I know of Allan variance, but I don't have anything
> else handy I can use for comparison. I also can't really afford to send one
> off for testing to a proper lab. In looking at
> http://tf.nist.gov/general/pdf/2297.pdf, it suggests that my results are
> relatively poor compared to what a GPSDO can achieve (more like 10^-12
> rather than 10^-9), but I assume that they’re able to use a higher
> frequency GPS reference than just 1 PPS (and they’re a lot pricier).
>
> What else can I do to try and characterize the performance? If mine is
> performing far more poorly than the same price ($175) can buy elsewhere,
> then what am I doing wrong?
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Bob Stewart]

Hi Nick,
In fact, if no-one else has volunteered, contact me offline and I'll run a test 
for you on my equipment, which is an HP5370A and a Symmetricom PRS-45A Cesium 
standard.  

bob at evoria dot net
  From: Tom Van Baak 
 To: Discussion of precise time and frequency measurement  
 Sent: Sunday, August 16, 2015 2:31 PM
 Subject: Re: [time-nuts] I've designed a GPSDO, but how "good" is it?
   
Hi Nick,

Nice project. Thanks for sharing.

I was hoping someone would someday use a cheap Sparkfun / Parallax / Adafruit 
GPS to make a low-cost GPSDO. Mostly what people on this list do is go to the 
extreme of using serious GPS timing receivers (such as Oncore M12+T, or 
ublox-5T or 6T or 8T) but those require significant amounts of configuration, 
tuning, survey, etc. to meet ultimate performance levels.

The good thing about using a cheap hobbyist-grade 3D GPS/1PPS receiver is that 
they work anywhere, without fiddling or survey, within seconds of power-on. Ok, 
you lose a few ns of precision compared to serious receivers -- but for a TCXO 
that doesn't matter.

Anyway, to answer your question -- to measure its true performance you only 
need two things. 1) a phase meter (or time interval counter) that's good to 1 
ns or better, and 2) a local reference standard that's maybe 10x better than 
the TCXO and the Adafruit GPS. Usually that means a cesium standard, or 
supremely qualified GPSDO, or equivalent.

A number of us here on the time-nuts list have such equipment at home. And 
unlike professional labs, we will do it for free/fun if you loan the GPSDO for 
a week.

If you want to play with raw timing data from an Adafruit GPS board see file 
gps-mtk3339.txt.gz under http://www.leapsecond.com/pages/gpsdo-sim/ and then 
use TimeLab for phase, frequency, and Allan deviation analysis 
(http://www.ke5fx.com/timelab/readme.htm).

/tvb

- Original Message - 
From: "Nick Sayer via time-nuts" 
To: 
Sent: Sunday, August 16, 2015 11:47 AM
Subject: [time-nuts] I've designed a GPSDO, but how "good" is it?


I’ve designed and make and sell a GPSDO on Tindie 
(https://hackaday.io/project/6872-gps-disciplined-tcxo). It’s brand new - I’ve 
sold a handful of them so far. So as to make this post not *entirely* 
self-serving, what I would like is some further guidance on how I can better 
characterize its performance.

The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module - a 
PA6H). The manufacturer claims an accuracy of ±10 ns, but that's accuracy 
relative to the true start of the GPS second. They don’t make any claim for 
stability.

The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term (though 
they don’t say how short that term is) stability of 1 ppb. The absolute 
accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and the control 
voltage is steered by GPS feedback.

The feedback loop takes samples over a 100 second period. That gives me an 
error sample with a granularity of 1 ppb. I keep a rolling sample window of 10 
samples to get an error count over 1000 seconds. I've kept track of both of 
these values for extended periods (days) as well as logging the DAC value (the 
number that's proportional to the control voltage). The 1000 second sample 
window error averages zero, and it almost never exceeds ±7 (every once in a 
while if I physically move it, it will show a momentary error glitch, but that 
shows up in the short term feedback sampling too). The 100 second samples are 
almost all 0 or ±1, with an occasional ±2 showing up. As I said before, if I 
bonk the oscillator, it may briefly show a ±6 or so for one sample.

If I pit two of them against each other on a scope and take a time lapse video 
(http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they stay mostly 
locked with occasional periods of drift. I sort of assume that that represents 
periods where the two GPS receivers disagree as they decide differently how to 
select among the available satellites.

I've been saying out loud that the oscillator is ±1 ppb from GPS over the 1000 
second window. I know of Allan variance, but I don't have anything else handy I 
can use for comparison. I also can't really afford to send one off for testing 
to a proper lab. In looking at http://tf.nist.gov/general/pdf/2297.pdf, it 
suggests that my results are relatively poor compared to what a GPSDO can 
achieve (more like 10^-12 rather than 10^-9), but I assume that they’re able to 
use a higher frequency GPS reference than just 1 PPS (and they’re a lot 
pricier).

What else can I do to try and characterize the performance? If mine is 
performing far more poorly than the same price ($175) can buy elsewhere, then 
what am I doing wrong?

___
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Graham / KE9H]

Nick:

>From your description, it sounds like you have a frequency locked loop with
a maximum frequency sensitivity of 1 ppb, as opposed to a phase locked loop.

At the end of the 100 second count period, do you start over with a counter
set to zero, or do you carry forward any error from the previous period?

--- Graham

==




On Sun, Aug 16, 2015 at 2:31 PM, Tom Van Baak  wrote:

> Hi Nick,
>
> Nice project. Thanks for sharing.
>
> I was hoping someone would someday use a cheap Sparkfun / Parallax /
> Adafruit GPS to make a low-cost GPSDO. Mostly what people on this list do
> is go to the extreme of using serious GPS timing receivers (such as Oncore
> M12+T, or ublox-5T or 6T or 8T) but those require significant amounts of
> configuration, tuning, survey, etc. to meet ultimate performance levels.
>
> The good thing about using a cheap hobbyist-grade 3D GPS/1PPS receiver is
> that they work anywhere, without fiddling or survey, within seconds of
> power-on. Ok, you lose a few ns of precision compared to serious receivers
> -- but for a TCXO that doesn't matter.
>
> Anyway, to answer your question -- to measure its true performance you
> only need two things. 1) a phase meter (or time interval counter) that's
> good to 1 ns or better, and 2) a local reference standard that's maybe 10x
> better than the TCXO and the Adafruit GPS. Usually that means a cesium
> standard, or supremely qualified GPSDO, or equivalent.
>
> A number of us here on the time-nuts list have such equipment at home. And
> unlike professional labs, we will do it for free/fun if you loan the GPSDO
> for a week.
>
> If you want to play with raw timing data from an Adafruit GPS board see
> file gps-mtk3339.txt.gz under http://www.leapsecond.com/pages/gpsdo-sim/
> and then use TimeLab for phase, frequency, and Allan deviation analysis (
> http://www.ke5fx.com/timelab/readme.htm).
>
> /tvb
>
> - Original Message -
> From: "Nick Sayer via time-nuts" 
> To: 
> Sent: Sunday, August 16, 2015 11:47 AM
> Subject: [time-nuts] I've designed a GPSDO, but how "good" is it?
>
>
> I’ve designed and make and sell a GPSDO on Tindie (
> https://hackaday.io/project/6872-gps-disciplined-tcxo). It’s brand new -
> I’ve sold a handful of them so far. So as to make this post not *entirely*
> self-serving, what I would like is some further guidance on how I can
> better characterize its performance.
>
> The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module
> - a PA6H). The manufacturer claims an accuracy of ±10 ns, but that's
> accuracy relative to the true start of the GPS second. They don’t make any
> claim for stability.
>
> The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term
> (though they don’t say how short that term is) stability of 1 ppb. The
> absolute accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and
> the control voltage is steered by GPS feedback.
>
> The feedback loop takes samples over a 100 second period. That gives me an
> error sample with a granularity of 1 ppb. I keep a rolling sample window of
> 10 samples to get an error count over 1000 seconds. I've kept track of both
> of these values for extended periods (days) as well as logging the DAC
> value (the number that's proportional to the control voltage). The 1000
> second sample window error averages zero, and it almost never exceeds ±7
> (every once in a while if I physically move it, it will show a momentary
> error glitch, but that shows up in the short term feedback sampling too).
> The 100 second samples are almost all 0 or ±1, with an occasional ±2
> showing up. As I said before, if I bonk the oscillator, it may briefly show
> a ±6 or so for one sample.
>
> If I pit two of them against each other on a scope and take a time lapse
> video (http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they
> stay mostly locked with occasional periods of drift. I sort of assume that
> that represents periods where the two GPS receivers disagree as they decide
> differently how to select among the available satellites.
>
> I've been saying out loud that the oscillator is ±1 ppb from GPS over the
> 1000 second window. I know of Allan variance, but I don't have anything
> else handy I can use for comparison. I also can't really afford to send one
> off for testing to a proper lab. In looking at
> http://tf.nist.gov/general/pdf/2297.pdf, it suggests that my results are
> relatively poor compared to what a GPSDO can achieve (more like 10^-12
> rather than 10^-9), but I assume that they’re able to use a higher
> frequency GPS reference than just 1 PPS (and they’re a lot pricier).
>
> What else can I do to try and characterize the performance? If mine is
> performing far more poorly than the same price ($175) can buy elsewhere,
> then what am I doing wrong?
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nu

Re: [time-nuts] Troubleshooting Fluke PM6681

[davidh]

Magnus,

I have a few of these counters and would love to see the details of the 
calibration process you mention.


Cheers.

david

On 17/08/2015 5:16 AM, Magnus Danielson wrote:

Ole,

I checked with a former Pendulum employee, and free off memory, he
recommend trimming up the 100 MHz until Error 2 does not show. Sensing
it directly can be difficult, FET-probe essentially mandatory.
Indirectly a 10 MHz is possible. A problem is that trimming with the
hood off causes a different thermal setup than when the hood is on. If
you dare, make a hole in the hood so that you can trim it with the hood
on, that is what they did.

CMOS backup battery eventually fails, and then you need to replace it
and re-calibrate it. I have the details jotted down, but it seems that
this is not your issue.

Cheers,
Magnus

On 08/16/2015 12:20 PM, Ole Petter Ronningen wrote:

Hello.

I have a Fluke PM6681 that has issues. When I got it, it gave results all
over the place, but after adjusting the 100Mhz multiplier-chain, it seems
to be much better; at least I get std.deviationwell within spec using a
split pulse to input A and B, 100 samples. I'd like to get it
professionally calibrated, but I don't want to send it in with known
issues
- the cost of calibration will not be refunded if the instrument can
not be
calibrated, and I believe it is no longer repairable.

So, the issue is that it fails the ASIC test (test 6), with err 2.The
service-guide lists a number of signals to be checked in test-mode, but I
am not able to see any of them. Since the counter seems to function, I
can
only conclude that the signals are not present due to this error.. (Or
that
I am mistreading the guide and looking in the wrong place, probably at
least as likely..)

Anyway, I cant seem to find a description of this particular error, does
anyone know what it means?

Thanks,
Ole
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Bob Camp]

Hi

Alll of the GPSDO’s that NIST is looking at are 1 PPS based. What’s different 
about them:

1) The OCXO’s (or Rb’s) are stable to 0,001 ppb at 1 second
2) The GPS is designed for timing (and spec’d by an outfit that understands 
timing — see below) (uBlox maybe)
3) The GPS puts out a sawtooth correction and the loop uses it.
4) The GPS PPS and OCXO are compared at the sub nanosecond level to feed the 
loop
5) The loop parameters are optimized such that the GPS does not feed though 
much at < 1,000 seconds
6) The OCXO is stable enough that it can chug along without help from the GPS 
for hundreds of seconds 

That’s the short list, there is probably a much more detailed list, but that 
gets into a lot of “that depends” 
sort of stuff. With $25 eBay “treasures” popping up from time to time the cost 
target is very fluid on these 
things.

One thing to take a look at: NIST has papers on L1 ionosphere correction (= 
lack of). Note from the papers how it must 
impact your module. After you dig a bit into that 10 to 50 ns per day variable, 
take a look again at the 
10 ns manufacturer’s accuracy claim in your module...

Bob

> On Aug 16, 2015, at 2:47 PM, Nick Sayer via time-nuts  
> wrote:
> 
> I’ve designed and make and sell a GPSDO on Tindie 
> (https://hackaday.io/project/6872-gps-disciplined-tcxo). It’s brand new - 
> I’ve sold a handful of them so far. So as to make this post not *entirely* 
> self-serving, what I would like is some further guidance on how I can better 
> characterize its performance.
> 
> The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module - 
> a PA6H). The manufacturer claims an accuracy of ±10 ns, but that's accuracy 
> relative to the true start of the GPS second. They don’t make any claim for 
> stability.
> 
> The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term 
> (though they don’t say how short that term is) stability of 1 ppb. The 
> absolute accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and 
> the control voltage is steered by GPS feedback.
> 
> The feedback loop takes samples over a 100 second period. That gives me an 
> error sample with a granularity of 1 ppb. I keep a rolling sample window of 
> 10 samples to get an error count over 1000 seconds. I've kept track of both 
> of these values for extended periods (days) as well as logging the DAC value 
> (the number that's proportional to the control voltage). The 1000 second 
> sample window error averages zero, and it almost never exceeds ±7 (every once 
> in a while if I physically move it, it will show a momentary error glitch, 
> but that shows up in the short term feedback sampling too). The 100 second 
> samples are almost all 0 or ±1, with an occasional ±2 showing up. As I said 
> before, if I bonk the oscillator, it may briefly show a ±6 or so for one 
> sample.
> 
> If I pit two of them against each other on a scope and take a time lapse 
> video (http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they 
> stay mostly locked with occasional periods of drift. I sort of assume that 
> that represents periods where the two GPS receivers disagree as they decide 
> differently how to select among the available satellites.
> 
> I've been saying out loud that the oscillator is ±1 ppb from GPS over the 
> 1000 second window. I know of Allan variance, but I don't have anything else 
> handy I can use for comparison. I also can't really afford to send one off 
> for testing to a proper lab. In looking at 
> http://tf.nist.gov/general/pdf/2297.pdf, it suggests that my results are 
> relatively poor compared to what a GPSDO can achieve (more like 10^-12 rather 
> than 10^-9), but I assume that they’re able to use a higher frequency GPS 
> reference than just 1 PPS (and they’re a lot pricier).
> 
> What else can I do to try and characterize the performance? If mine is 
> performing far more poorly than the same price ($175) can buy elsewhere, then 
> what am I doing wrong?
> 
> ___
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> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] Troubleshooting Fluke PM6681

[Tom Knox]

I am not sure if this could be related but I have worked on several of these 
and found the power supply caps can often be a problem and cause the instrument 
to display a wide range of issues related to the excess PS noise. This problem 
is more common with the 6681R which runs a bit hotter.
Cheers;
Thomas Knox



> Date: Sun, 16 Aug 2015 21:16:22 +0200
> From: mag...@rubidium.dyndns.org
> To: time-nuts@febo.com
> CC: mag...@rubidium.se
> Subject: Re: [time-nuts] Troubleshooting Fluke PM6681
> 
> Ole,
> 
> I checked with a former Pendulum employee, and free off memory, he 
> recommend trimming up the 100 MHz until Error 2 does not show. Sensing 
> it directly can be difficult, FET-probe essentially mandatory. 
> Indirectly a 10 MHz is possible. A problem is that trimming with the 
> hood off causes a different thermal setup than when the hood is on. If 
> you dare, make a hole in the hood so that you can trim it with the hood 
> on, that is what they did.
> 
> CMOS backup battery eventually fails, and then you need to replace it 
> and re-calibrate it. I have the details jotted down, but it seems that 
> this is not your issue.
> 
> Cheers,
> Magnus
> 
> On 08/16/2015 12:20 PM, Ole Petter Ronningen wrote:
> > Hello.
> >
> > I have a Fluke PM6681 that has issues. When I got it, it gave results all
> > over the place, but after adjusting the 100Mhz multiplier-chain, it seems
> > to be much better; at least I get std.deviationwell within spec using a
> > split pulse to input A and B, 100 samples. I'd like to get it
> > professionally calibrated, but I don't want to send it in with known issues
> > - the cost of calibration will not be refunded if the instrument can not be
> > calibrated, and I believe it is no longer repairable.
> >
> > So, the issue is that it fails the ASIC test (test 6), with err 2.The
> > service-guide lists a number of signals to be checked in test-mode, but I
> > am not able to see any of them. Since the counter seems to function, I can
> > only conclude that the signals are not present due to this error.. (Or that
> > I am mistreading the guide and looking in the wrong place, probably at
> > least as likely..)
> >
> > Anyway, I cant seem to find a description of this particular error, does
> > anyone know what it means?
> >
> > Thanks,
> > Ole
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to 
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Nick Sayer via time-nuts]

> On Aug 16, 2015, at 12:31 PM, Tom Van Baak  wrote:
> 
> Anyway, to answer your question -- to measure its true performance you only 
> need two things. 1) a phase meter (or time interval counter) that's good to 1 
> ns or better, and 2) a local reference standard that's maybe 10x better than 
> the TCXO and the Adafruit GPS. Usually that means a cesium standard, or 
> supremely qualified GPSDO, or equivalent.

I have a frequency counter, but it’s not a phase meter. I have a scope, but I 
assume that trying to use a ruler with scope traces isn’t the textbook way of 
doing that. :D

I have considered in the past buying a used rubidium standard off eBay, but 
have hesitated because I don’t know how much life there is left in the tube, 
and I just have to take it on faith that it’s stable and accurate. I have 
somewhat more faith in the GPS PPS, but clearly that has limits.

> 
> A number of us here on the time-nuts list have such equipment at home. And 
> unlike professional labs, we will do it for free/fun if you loan the GPSDO 
> for a week.

I will happily *give* one to someone if they would be willing to help a 
relative newbie with this stuff.

Just one though. They’re kind of expensive to build. :D

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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Magnus Danielson]

Nick,

To get you started, I would use a free-running Rubidium and a 
time-interval counter. The rubidium will be having the wrong frequency, 
but that should cancel out in the Allan deviation processing. The drift 
of the rubidium clock will form a limit, but you can overcome that by 
using either Hadamard deviation or do drift-removal. Collect your data 
with TimeLab and you have a good starting-point. The time interval 
counter should at least have 1 ns single-shot resolution, the more the 
merrier. Try grab a SR620 or HP5370 or something.


The setup I propose is not optimum, but should give you some interesting 
result and hopefully in the right direction.


If you can, recording the GPSDOs state such as time-error, EFC and other 
key parameters in parallel can be very helpful in analysis, so make sure 
it pops that out so you can have a time-stamped file with it.


The rubidum trace will be the external "judge" of what movements it 
really did except for long-term where the rubidiums systematics starts 
to cave in.


There comes that point when a GPSDO vendor needs to turn on their 
Cesium, but I think you have some issues and things to learn before you 
need to do that. Had to support one GPSDO vendor over my mobile phone at 
one time as to how to bring up the cesium, so much fun. They reached 
that point for the right reason. :)


Cheers,
Magnus

On 08/16/2015 08:47 PM, Nick Sayer via time-nuts wrote:

I’ve designed and make and sell a GPSDO on Tindie 
(https://hackaday.io/project/6872-gps-disciplined-tcxo). It’s brand new - I’ve 
sold a handful of them so far. So as to make this post not *entirely* 
self-serving, what I would like is some further guidance on how I can better 
characterize its performance.

The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module - a 
PA6H). The manufacturer claims an accuracy of ±10 ns, but that's accuracy 
relative to the true start of the GPS second. They don’t make any claim for 
stability.

The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term (though 
they don’t say how short that term is) stability of 1 ppb. The absolute 
accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and the control 
voltage is steered by GPS feedback.

The feedback loop takes samples over a 100 second period. That gives me an 
error sample with a granularity of 1 ppb. I keep a rolling sample window of 10 
samples to get an error count over 1000 seconds. I've kept track of both of 
these values for extended periods (days) as well as logging the DAC value (the 
number that's proportional to the control voltage). The 1000 second sample 
window error averages zero, and it almost never exceeds ±7 (every once in a 
while if I physically move it, it will show a momentary error glitch, but that 
shows up in the short term feedback sampling too). The 100 second samples are 
almost all 0 or ±1, with an occasional ±2 showing up. As I said before, if I 
bonk the oscillator, it may briefly show a ±6 or so for one sample.

If I pit two of them against each other on a scope and take a time lapse video 
(http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they stay mostly 
locked with occasional periods of drift. I sort of assume that that represents 
periods where the two GPS receivers disagree as they decide differently how to 
select among the available satellites.

I've been saying out loud that the oscillator is ±1 ppb from GPS over the 1000 
second window. I know of Allan variance, but I don't have anything else handy I 
can use for comparison. I also can't really afford to send one off for testing 
to a proper lab. In looking at http://tf.nist.gov/general/pdf/2297.pdf, it 
suggests that my results are relatively poor compared to what a GPSDO can 
achieve (more like 10^-12 rather than 10^-9), but I assume that they’re able to 
use a higher frequency GPS reference than just 1 PPS (and they’re a lot 
pricier).

What else can I do to try and characterize the performance? If mine is 
performing far more poorly than the same price ($175) can buy elsewhere, then 
what am I doing wrong?

___
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Re: [time-nuts] I've designed a GPSDO, but how "good" is it?

[Tom Van Baak]

Hi Nick,

Nice project. Thanks for sharing.

I was hoping someone would someday use a cheap Sparkfun / Parallax / Adafruit 
GPS to make a low-cost GPSDO. Mostly what people on this list do is go to the 
extreme of using serious GPS timing receivers (such as Oncore M12+T, or 
ublox-5T or 6T or 8T) but those require significant amounts of configuration, 
tuning, survey, etc. to meet ultimate performance levels.

The good thing about using a cheap hobbyist-grade 3D GPS/1PPS receiver is that 
they work anywhere, without fiddling or survey, within seconds of power-on. Ok, 
you lose a few ns of precision compared to serious receivers -- but for a TCXO 
that doesn't matter.

Anyway, to answer your question -- to measure its true performance you only 
need two things. 1) a phase meter (or time interval counter) that's good to 1 
ns or better, and 2) a local reference standard that's maybe 10x better than 
the TCXO and the Adafruit GPS. Usually that means a cesium standard, or 
supremely qualified GPSDO, or equivalent.

A number of us here on the time-nuts list have such equipment at home. And 
unlike professional labs, we will do it for free/fun if you loan the GPSDO for 
a week.

If you want to play with raw timing data from an Adafruit GPS board see file 
gps-mtk3339.txt.gz under http://www.leapsecond.com/pages/gpsdo-sim/ and then 
use TimeLab for phase, frequency, and Allan deviation analysis 
(http://www.ke5fx.com/timelab/readme.htm).

/tvb

- Original Message - 
From: "Nick Sayer via time-nuts" 
To: 
Sent: Sunday, August 16, 2015 11:47 AM
Subject: [time-nuts] I've designed a GPSDO, but how "good" is it?


I’ve designed and make and sell a GPSDO on Tindie 
(https://hackaday.io/project/6872-gps-disciplined-tcxo). It’s brand new - I’ve 
sold a handful of them so far. So as to make this post not *entirely* 
self-serving, what I would like is some further guidance on how I can better 
characterize its performance.

The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module - a 
PA6H). The manufacturer claims an accuracy of ±10 ns, but that's accuracy 
relative to the true start of the GPS second. They don’t make any claim for 
stability.

The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term (though 
they don’t say how short that term is) stability of 1 ppb. The absolute 
accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and the control 
voltage is steered by GPS feedback.

The feedback loop takes samples over a 100 second period. That gives me an 
error sample with a granularity of 1 ppb. I keep a rolling sample window of 10 
samples to get an error count over 1000 seconds. I've kept track of both of 
these values for extended periods (days) as well as logging the DAC value (the 
number that's proportional to the control voltage). The 1000 second sample 
window error averages zero, and it almost never exceeds ±7 (every once in a 
while if I physically move it, it will show a momentary error glitch, but that 
shows up in the short term feedback sampling too). The 100 second samples are 
almost all 0 or ±1, with an occasional ±2 showing up. As I said before, if I 
bonk the oscillator, it may briefly show a ±6 or so for one sample.

If I pit two of them against each other on a scope and take a time lapse video 
(http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they stay mostly 
locked with occasional periods of drift. I sort of assume that that represents 
periods where the two GPS receivers disagree as they decide differently how to 
select among the available satellites.

I've been saying out loud that the oscillator is ±1 ppb from GPS over the 1000 
second window. I know of Allan variance, but I don't have anything else handy I 
can use for comparison. I also can't really afford to send one off for testing 
to a proper lab. In looking at http://tf.nist.gov/general/pdf/2297.pdf, it 
suggests that my results are relatively poor compared to what a GPSDO can 
achieve (more like 10^-12 rather than 10^-9), but I assume that they’re able to 
use a higher frequency GPS reference than just 1 PPS (and they’re a lot 
pricier).

What else can I do to try and characterize the performance? If mine is 
performing far more poorly than the same price ($175) can buy elsewhere, then 
what am I doing wrong?

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Re: [time-nuts] Trimble GPS board

[Bob Camp]

Hi

I think you will find that on the part you are looking at:

TPN = Trimble Part Number
57964-15 = Trimble’s part number on the module
SEC CODE = probably more relevant to the module that the OCXO info

Date Code (on OCXO) 0826 = it was made sometime around the middle of 2008

One would *guess* that it is a more modern version of the TBolt.

Bob


> On Aug 16, 2015, at 10:52 AM, Bob Benward  wrote:
> 
> Hi all,
> 
> Does anyone have any information or experience with this small Trimble
> GPSDO?  There doesn't seem to be any associated model number other than the
> model of the OCXO (63090).  I am looking for software, command codes, or
> hookup schematics, can anyone help?
> 
> 
> 
> http://www.ebay.com/itm/141734507722?_trksid=p2057872.m2749.l2649
>  e=STRK%3AMEBIDX%3AIT> &ssPageName=STRK%3AMEBIDX%3AIT
> 
> 
> 
> Thanks,
> 
> Bob
> 
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Re: [time-nuts] Troubleshooting Fluke PM6681

[Magnus Danielson]

Ole,

I checked with a former Pendulum employee, and free off memory, he 
recommend trimming up the 100 MHz until Error 2 does not show. Sensing 
it directly can be difficult, FET-probe essentially mandatory. 
Indirectly a 10 MHz is possible. A problem is that trimming with the 
hood off causes a different thermal setup than when the hood is on. If 
you dare, make a hole in the hood so that you can trim it with the hood 
on, that is what they did.


CMOS backup battery eventually fails, and then you need to replace it 
and re-calibrate it. I have the details jotted down, but it seems that 
this is not your issue.


Cheers,
Magnus

On 08/16/2015 12:20 PM, Ole Petter Ronningen wrote:

Hello.

I have a Fluke PM6681 that has issues. When I got it, it gave results all
over the place, but after adjusting the 100Mhz multiplier-chain, it seems
to be much better; at least I get std.deviationwell within spec using a
split pulse to input A and B, 100 samples. I'd like to get it
professionally calibrated, but I don't want to send it in with known issues
- the cost of calibration will not be refunded if the instrument can not be
calibrated, and I believe it is no longer repairable.

So, the issue is that it fails the ASIC test (test 6), with err 2.The
service-guide lists a number of signals to be checked in test-mode, but I
am not able to see any of them. Since the counter seems to function, I can
only conclude that the signals are not present due to this error.. (Or that
I am mistreading the guide and looking in the wrong place, probably at
least as likely..)

Anyway, I cant seem to find a description of this particular error, does
anyone know what it means?

Thanks,
Ole
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[time-nuts] I've designed a GPSDO, but how "good" is it?

[Nick Sayer via time-nuts]

I’ve designed and make and sell a GPSDO on Tindie 
(https://hackaday.io/project/6872-gps-disciplined-tcxo). It’s brand new - I’ve 
sold a handful of them so far. So as to make this post not *entirely* 
self-serving, what I would like is some further guidance on how I can better 
characterize its performance.

The GPS reference is a 1 pps signal (It’s the Adafruit Ultimate GPS module - a 
PA6H). The manufacturer claims an accuracy of ±10 ns, but that's accuracy 
relative to the true start of the GPS second. They don’t make any claim for 
stability.

The oscillator itself (Connor Winfield DOT050V 10 MHz) has a short-term (though 
they don’t say how short that term is) stability of 1 ppb. The absolute 
accuracy of it is (I assume) irrelevant, because it’s a VCTCXO and the control 
voltage is steered by GPS feedback.

The feedback loop takes samples over a 100 second period. That gives me an 
error sample with a granularity of 1 ppb. I keep a rolling sample window of 10 
samples to get an error count over 1000 seconds. I've kept track of both of 
these values for extended periods (days) as well as logging the DAC value (the 
number that's proportional to the control voltage). The 1000 second sample 
window error averages zero, and it almost never exceeds ±7 (every once in a 
while if I physically move it, it will show a momentary error glitch, but that 
shows up in the short term feedback sampling too). The 100 second samples are 
almost all 0 or ±1, with an occasional ±2 showing up. As I said before, if I 
bonk the oscillator, it may briefly show a ±6 or so for one sample.

If I pit two of them against each other on a scope and take a time lapse video 
(http://www.youtube.com/watch?v=9HkeCI90i44), you can see that they stay mostly 
locked with occasional periods of drift. I sort of assume that that represents 
periods where the two GPS receivers disagree as they decide differently how to 
select among the available satellites.

I've been saying out loud that the oscillator is ±1 ppb from GPS over the 1000 
second window. I know of Allan variance, but I don't have anything else handy I 
can use for comparison. I also can't really afford to send one off for testing 
to a proper lab. In looking at http://tf.nist.gov/general/pdf/2297.pdf, it 
suggests that my results are relatively poor compared to what a GPSDO can 
achieve (more like 10^-12 rather than 10^-9), but I assume that they’re able to 
use a higher frequency GPS reference than just 1 PPS (and they’re a lot 
pricier).

What else can I do to try and characterize the performance? If mine is 
performing far more poorly than the same price ($175) can buy elsewhere, then 
what am I doing wrong?

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[time-nuts] Trimble GPS board

[Arthur Dent]

"Does anyone have any information or experience with this small
Trimble GPSDO?"

If you search on Ebay for more of the same GPSDO you will find
that there are several sellers offering these units. The units
are a Trimble 57963 (x) where x is a revision letter. Some have
a different oscillator number and some have a shield over the
GPS section but I don't know the differences-yet. I have 2 that
should be here soon if all goes well. Read the listings and you
will see that they have an RS-232 interface and run on 5.6 to
6VDC if you believe the given info. Some of the sellers are
building these into nice boxes and selling them for $150 if you
want a ready made unit. Some of the listings have PC screen shots
that show some information. Seems to track 12 SVs so these are
pretty new. I 'think' the date is 2009 from some chip numbers.

-Arthur
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[time-nuts] Trimble GPS board

[Bob Benward]

Hi all,

Does anyone have any information or experience with this small Trimble
GPSDO?  There doesn't seem to be any associated model number other than the
model of the OCXO (63090).  I am looking for software, command codes, or
hookup schematics, can anyone help?

 

http://www.ebay.com/itm/141734507722?_trksid=p2057872.m2749.l2649
 &ssPageName=STRK%3AMEBIDX%3AIT

 

Thanks,

Bob

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[time-nuts] Troubleshooting Fluke PM6681

[Ole Petter Ronningen]

Hello.

I have a Fluke PM6681 that has issues. When I got it, it gave results all
over the place, but after adjusting the 100Mhz multiplier-chain, it seems
to be much better; at least I get std.deviationwell within spec using a
split pulse to input A and B, 100 samples. I'd like to get it
professionally calibrated, but I don't want to send it in with known issues
- the cost of calibration will not be refunded if the instrument can not be
calibrated, and I believe it is no longer repairable.

So, the issue is that it fails the ASIC test (test 6), with err 2.The
service-guide lists a number of signals to be checked in test-mode, but I
am not able to see any of them. Since the counter seems to function, I can
only conclude that the signals are not present due to this error.. (Or that
I am mistreading the guide and looking in the wrong place, probably at
least as likely..)

Anyway, I cant seem to find a description of this particular error, does
anyone know what it means?

Thanks,
Ole
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Re: [time-nuts] 58503A stats

[Magnus Danielson]

Alan,

Do not worry about that sky-view.
I'd guess your issue is more local, as on your roof.
Still, in timing you can afford to drop a lot of satellites if you only 
got a good fixed position.


Cheers,
Magnus

On 08/04/2015 11:02 AM, Alan Ambrose wrote:

p.s. here's the view south taken from about 2m below the antenna:

https://www.dropbox.com/s/zejod2sfi4iogq1/IMG_460371644.JPG?dl=0

Alan

From: Alan Ambrose
Sent: 04 August 2015 9:50 AM
To: 'time-nuts@febo.com' 
Subject: 58503A stats

Hi,

Here is a screen capture from excellent Ulrich's Z38XX program:

https://www.dropbox.com/s/6p5dr8apsftrckf/Z38XX-1.JPG?dl=0

This is the first time that I've seen this output and I have a couple of questions. 
I should explain that the antenna is fairly well situated in London UK with a good 
view south with no obstacles and ~5m above and away from any other roofs. There are 
3 small skyscrapers about ½ mile distance at 140° azimuth and 15° elevation. There 
are however obstructions about 4m away to the NW & SW (around 240° and 330°) 
limiting the view to 45° elevation. The device is a 58503A (it might be some dodgy 
far east 're-manufacture') with tracking of max 6 active sats. I've set the 
elevation mask temporarily to 0° to get the fullest map - as you can see that 
doesn't make much difference.

+ I was surprised to see such a noisy EFC signal - I assumed that the EFC 
changed v. gradually on a slow loop - maybe with temperature and aging. However 
there's a lot of high frequency crud there which I don't understand.
+ The 'holdover uncertainty predict' seems to go on a daily loop along with the 
EFC from 1.5 to 2.4us - presumably with temperature? If that's normal behaviour 
it suggests that the DOCXO isn't that well thermally managed?
+ The holdover uncertainty and the 1 pps variance don't relate at all to the 
occasional drop down to 3 sats. So some other effect is at work here - is this 
just ionosphere and general short term GPS inaccuracy only?
+ The time stability measures are not credible in their relentless plunge 
downward?
+ The azimuth/elevation chart looks about right except for the view to the 
south (say 150° to 220°) where I would expect at least as good as the view to 
the east - say by another 20° of elevation? (There's a point at 0/0 which I'm 
sure is an artefact caused by temporary '---' characters in the El/Az output of 
the device.) I don't have many ideas on this as the view is dead good. Any 
thoughts?
+ There's v little below 20° elevation - I think the view is clear though for 
most of the S azimuth down to ~0°. Is this simply because the device tends to 
ignore low elevation sats in its tracking because it has better ones to play 
with?

Would all you greybeards out there give the benefit of your hard-won experience 
and/or maybe there are other people's charts to compare with?

Regards, Alan



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