Author Topic: bg7tbl gpsdo master reference  (Read 126702 times)

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Online edpalmer42

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Re: bg7tbl gpsdo master reference
« Reply #100 on: August 26, 2015, 04:44:30 pm »
Here are some Timelab graphs showing the Lucent KS-24361 versus the latest BG7TBL attempt as well as the two 3rd-party units he is putting his logo on.

Very interesting!

If you ran the Allen Deviation graphs longer you'd see more of the behaviour of the units. 

I tried to run the Allan Deviation for longer, but for some reason Timelab just stops capturing after some time. It's not the value I set in the Acquisition settings, it stops even if I set it to only stop on Manual Termination.

Notice how they all line up on the left side of the graph?  That's the effect of your 53131A counter.  It's only when they deviate from that line that you see the interaction of the GPSDOs.

I suspected this. I even tried calibrating some of the other aspects of the counter like  offset, gain, and the Time Interval calibration. I think the offset and gain calibrations were fine, but the time interval calibration made things worse. This counter has a "quick" mode of calibration of that which can be done without any fancy equipment, but the fine mode requires things I don't have. So by doing the quick cal, I think I actually made it worse.

The phase graph really shows the frequency error doesn't it?  If you hit the 'r' key, TimeLab will take a linear best fit of each graph and then subtract it from the graph.  The frequency offset will disappear and you'll see the short-term comparison of the units.  This would give you an idea what would happen if you used the 10 MHz as a reference for your counter, generator, etc.
Ed

Take a gander at the updates on the Huawei/Star4+ unit above. This is looking like a really good option now that we have a management interface working.

I can't imagine why Timelab would just stop.  I've run it for days.  Does it just stop acquiring or does it pop up some kind of dialog box?

Calibration won't affect the sloped line on the left side of the Allen Deviation graphs.  That's determined by the counter's resolution.  Notice that at 1 second on the X-axis, the graphs are at about 7e-10.  The 53131A has a resolution of 500 ps, i.e. 5e-10.  That's not a coincidence.  The one second Allen Deviation is slightly higher than the counter's resolution.

I saw the info on the Oscilloquartz Star 4.  Very nice!  But I see that there are no more units available.  Hopefully some more will appear soon.

Ed
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #101 on: August 26, 2015, 05:45:57 pm »

I can't imagine why Timelab would just stop.  I've run it for days.  Does it just stop acquiring or does it pop up some kind of dialog box?

Calibration won't affect the sloped line on the left side of the Allen Deviation graphs.  That's determined by the counter's resolution.  Notice that at 1 second on the X-axis, the graphs are at about 7e-10.  The 53131A has a resolution of 500 ps, i.e. 5e-10.  That's not a coincidence.  The one second Allen Deviation is slightly higher than the counter's resolution.

I saw the info on the Oscilloquartz Star 4.  Very nice!  But I see that there are no more units available.  Hopefully some more will appear soon.

Ed

It just stops. I'll run another capture tonight and post the results to show you what happens.

My thinking on the calibration was that if the gain and offset setting could be causing triggering somewhere other than the ideal center crossing of the square wave, in turn leading to more jitter. Maybe not, but I figured it couldn't hurt to calibrate it.
« Last Edit: August 26, 2015, 05:51:37 pm by motocoder »
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #102 on: August 26, 2015, 11:46:01 pm »
Ok, here are some screen grabs showing the issue. The first image shows that it's just stopped sampling at 200,000 points, even though this is far short of the 10,000 seconds I told it to capture. The second graph shows the settings that I used.

Note that it says "Acquiring (100%)" although this does not show up on the screen capture. It was set to capture 10,000 seconds but to continue until manually stopped. It says it has captured 200,000 pts, and if you divide 10,000 seconds by the Sample Interval value it's automatically selected, 0.05s, this gives 200,000. I suspect the issue likes somewhere with the sample interval it chose. Perhaps it chose a number of sample points up front, but then used a different sample interval and so ended up finishing early. Still, it was told to continue until manually stopped, so it shouldn't have stopped...
« Last Edit: August 26, 2015, 11:58:55 pm by motocoder »
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #103 on: August 27, 2015, 12:58:32 am »
I see what the issue is. It IS capturing for 10,000 seconds, but that doesn't equate to an Allan Deviation graph with information at 10,000 seconds. If you go to the phase plot, you can see that it does run to 10,000 seconds.

I'm not sure why the setting to run until manually stopped isn't working, but I'll  just crank up the Trace Duration value and let it run longer.
 

Online edpalmer42

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Re: bg7tbl gpsdo master reference
« Reply #104 on: August 27, 2015, 03:06:00 am »
I see what the issue is. It IS capturing for 10,000 seconds, but that doesn't equate to an Allan Deviation graph with information at 10,000 seconds. If you go to the phase plot, you can see that it does run to 10,000 seconds.

I'm not sure why the setting to run until manually stopped isn't working, but I'll  just crank up the Trace Duration value and let it run longer.

You might want to ask John Miles about this.  It doesn't sound like it's doing what he intended.  If you hover your mouse over the 'Run Until' field you'll see some help text.  It sounds like it's supposed to be a moving window with the length that's set in 'Trace Duration'.  I've never used that setting.

By the way, if you want to find the noise floor of your counter, take any signal (i.e. the Lucent's 10 or 15 MHz), split it, either with an actual splitter or just a BNC 'T' adapter, and feed it through two different length cables to the A and B inputs.  Then measure the time delay between the inputs.  This is a best case measurement.  Graph the results and you'll see how your counter is performing.  Make sure that the cables can't move around or fall off the table.  That will affect the results.

Ed
 

Offline EV

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Re: bg7tbl gpsdo master reference
« Reply #105 on: August 27, 2015, 04:32:27 am »
Has somebody found monitor program for this trimble disciplined version BG7TBL 2015-07-17? Does Tboltmon work?
« Last Edit: August 27, 2015, 04:31:19 pm by EV »
 

Offline bingo600

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Re: bg7tbl gpsdo master reference
« Reply #106 on: August 27, 2015, 04:37:34 am »
By the way, if you want to find the noise floor of your counter, take any signal (i.e. the Lucent's 10 or 15 MHz), split it, either with an actual splitter or just a BNC 'T' adapter, and feed it through two different length cables to the A and B inputs.  Then measure the time delay between the inputs.  This is a best case measurement.  Graph the results and you'll see how your counter is performing.  Make sure that the cables can't move around or fall off the table.  That will affect the results.

Ed

Nice tip ed  :-+

I'll have to give it a try with my PM6680B , and maybe the 5370B

/Bingo
 

Online edpalmer42

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Re: bg7tbl gpsdo master reference
« Reply #107 on: August 27, 2015, 04:59:04 am »
By the way, if you want to find the noise floor of your counter, take any signal (i.e. the Lucent's 10 or 15 MHz), split it, either with an actual splitter or just a BNC 'T' adapter, and feed it through two different length cables to the A and B inputs.  Then measure the time delay between the inputs.  This is a best case measurement.  Graph the results and you'll see how your counter is performing.  Make sure that the cables can't move around or fall off the table.  That will affect the results.

Ed

Nice tip ed  :-+

I'll have to give it a try with my PM6680B , and maybe the 5370B

/Bingo

That idea isn't mine.  It came from Magnus.......or Tom.......or John........or Didier.....hell, I don't remember.  It was one of those nutty guys.  :)

Ed
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #108 on: August 27, 2015, 08:09:53 am »
You might want to ask John Miles about this.  It doesn't sound like it's doing what he intended.  If you hover your mouse over the 'Run Until' field you'll see some help text.  It sounds like it's supposed to be a moving window with the length that's set in 'Trace Duration'.  I've never used that setting.

I did read all that help text already. In any event, just setting the duration to 100,000s seems to have solved the immediate problem. It's currently got about 4000s of Allan Deviation captured, and it says "Acquiring (26%)" so it seems like we should at least get 10,000s outof it.

Also note - now that I have the Huawei/Star4+ management interface working, I can see that it's not yet switched itself into its holdover stability mode, so I expect performance here will get better as the crystal ages in and it switches into that mode and increases the time constant on the adjustment loop. These units are really nice, definitely my favorite now.


By the way, if you want to find the noise floor of your counter, take any signal (i.e. the Lucent's 10 or 15 MHz), split it, either with an actual splitter or just a BNC 'T' adapter, and feed it through two different length cables to the A and B inputs.  Then measure the time delay between the inputs.  This is a best case measurement.  Graph the results and you'll see how your counter is performing.  Make sure that the cables can't move around or fall off the table.  That will affect the results.

Ok, I will give that a try. I did try connecting the same signal via two equal length cables, and I can see that 500ps resolution pretty clearly. FOr that matter, I can see it when comparing two of the GPSDO. The short term readings all seen to jitter by that 500ps value (at least as near as I can tell trying to read a display that is updating tens of times a second).
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #109 on: August 27, 2015, 02:48:36 pm »
I see what the issue is. It IS capturing for 10,000 seconds, but that doesn't equate to an Allan Deviation graph with information at 10,000 seconds. If you go to the phase plot, you can see that it does run to 10,000 seconds.

I'm not sure why the setting to run until manually stopped isn't working, but I'll  just crank up the Trace Duration value and let it run longer.

You might want to ask John Miles about this.  It doesn't sound like it's doing what he intended.  If you hover your mouse over the 'Run Until' field you'll see some help text.  It sounds like it's supposed to be a moving window with the length that's set in 'Trace Duration'.  I've never used that setting.

By the way, if you want to find the noise floor of your counter, take any signal (i.e. the Lucent's 10 or 15 MHz), split it, either with an actual splitter or just a BNC 'T' adapter, and feed it through two different length cables to the A and B inputs.  Then measure the time delay between the inputs.  This is a best case measurement.  Graph the results and you'll see how your counter is performing.  Make sure that the cables can't move around or fall off the table.  That will affect the results.

Ed

It ws just my misunderstanding of how the ADEV calculation works.
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #110 on: August 27, 2015, 02:49:33 pm »
Has somebody found moitor program for this trimble disciplined version BG7TBL 2015-07-17? Does Tboltmon work?

No it does not. The only software that I know which works is opening a terminal session and typing in the command.
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #111 on: August 28, 2015, 04:21:43 am »
Ed - as requested - here is a longer Timelab capture for the Huawei. It stopped a bit earlier than I wanted, but I couldn't figure out how to extend the capture.

Reading the specs on this unit, I think my measurement set-up is not sufficient to really show what this GPSDO is capable of. It would be great if someone with something better than a 53131A counter could capture some data on this.

 

Offline Dragon88

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Re: bg7tbl gpsdo master reference
« Reply #112 on: August 28, 2015, 09:38:27 am »
I can see that it's not yet switched itself into its holdover stability mod

Hi

Holdover and position hold are two different things. Holdover is when a GPSDO loses GPS and tries to maintain performance without it. Position hold is when the initial survey completes and the GPSDO switches into timing mode.

How long is the default initial survey on these units? Is there a way to run a longer precision survey? (Especially in the one with the LEA-5T)

How good is the PPS signal on these things? One measurement you can try is the TI between a reference PPS and the PPS edge of the DUT. This will tell you how well it maintains alignment of the PPS throughout the day. You will likely need to offset the reference so that the measured value doesn't drift across zero or cause the 53131A to re-scale the units. You are still limited by the 500ps resolution, but drift will likely be +/- tens of ns, so there is still meaningful data to be seen.
 

Offline radioFlash

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Re: bg7tbl gpsdo master reference
« Reply #113 on: August 28, 2015, 11:40:50 am »
Management interface works too. It's very picky about end-of-line characters, which is a PITA when using Putty because it does not give you control over what it sends. You need to send "<command>;<cr><lf>".

Here's the response to the INV commands. The hardware and firmware versions are the same as yours.

INV=GPS STAR 4+,015880,1057,01,015881,0149,11022010,0010,8663-XS,0152;
This is:


INV=a,b,c,d,e,f,g,h,i;<cr><lf>
a: Name of the module (Max 12 char.) : GPS STAR 4+
b: Article number (Max. 6 characters) : 015880
c: Serial Number (Max: 6 characters) : 1057
d: Hardware version (Max. 2 characters): 01
e: Firmware article number (6 characters) : 015881
f: Firmware version (4 characters) : 0149
g: Date of test (format : DD/MM/YYYY) : 11/02/2010
h: Version of test system (Max. 4 characters) : 0010
i : Oscillator's type ( Max. 10 characters) : 8663-XS
j: FPGA version (4 characters) : 0152


Please post your units response to this command if you wire up the management interface. I'd like to see what range of firmware/hardware versions are out there.
Here are responses to some of the various management commands:

INV;
INV=GPS STAR 4+,015880,1508,01,015881,0149,14042010,0010,8663-XS,0152;

CONF;
CONF=200,200,A,+00:00,+0;

ALARM;
ALARM=9;

GPS_TIME;
GPS_TIME=1859,437242,30.06.15,23:59:59,00,17;

INFO_TRACK_SAT;
INFO_TRACK_SAT=8,
1,14,
2,18,
3,21,
4,22,
5,24,
6,29,
7,135,
8,138;

STATUS;
STATUS=3,O,T;

TEMPERATURE;
TEMPERATURE=+40.41;

TYPE;
TYPE=4554,BASE;

ATDC_STATUS;
ATDC_STATUS=1,990;

HOLD_PERF_STATUS;
HOLD_PERF_STATUS=0;

INFO_VIS_SAT;
INFO_VIS_SAT=16,
1,138,54,197,43,2,
2,18,55,308,43,2,
3,135,39,234,42,2,
4,29,36,181,45,2,
5,122,32,242,0,1,
6,22,25,274,38,2,
7,20,37,51,0,2,
8,21,69,352,17,2,
9,24,24,124,29,2,
10,13,16,39,0,2,
11,26,1,257,0,2,
12,14,15,209,41,2,
13,15,48,48,17,2,
14,27,10,320,0,2,
15,16,2,283,0,2,
16,10,165,0,0,1;
 

Online edpalmer42

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Re: bg7tbl gpsdo master reference
« Reply #114 on: August 28, 2015, 11:47:37 am »
Ed - as requested - here is a longer Timelab capture for the Huawei. It stopped a bit earlier than I wanted, but I couldn't figure out how to extend the capture.

Reading the specs on this unit, I think my measurement set-up is not sufficient to really show what this GPSDO is capable of. It would be great if someone with something better than a 53131A counter could capture some data on this.

Yes, I think you're right.  In your earlier graphs you could see that the BG7TBL unit was flattening out in the low e-12 range while it wasn't clear where the Lucent and Oscilloquartz units were going.  Now we know that your counter's performance has merged with what I call the 'GPS line'.  It's the approximate performance limit of any GPSDO.  Early in the 'economical frequency standard' thread I think I had it on one of my graphs.

Let me see now, so far you've got a counter that's good enough for all normal uses and *three* GPSDOs and now you're complaining that your counter isn't good enough.  Moto, you're a Time-Nut!   ;D

Ed
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #115 on: August 28, 2015, 01:31:29 pm »
INV=GPS STAR 4+,015880,1057,01,015881,0149,11022010,0010,8663-XS,0152;
This is:


INV=a,b,c,d,e,f,g,h,i;<cr><lf>
a: Name of the module (Max 12 char.) : GPS STAR 4+
b: Article number (Max. 6 characters) : 015880
c: Serial Number (Max: 6 characters) : 1057
d: Hardware version (Max. 2 characters): 01
e: Firmware article number (6 characters) : 015881
f: Firmware version (4 characters) : 0149
g: Date of test (format : DD/MM/YYYY) : 11/02/2010
h: Version of test system (Max. 4 characters) : 0010
i : Oscillator's type ( Max. 10 characters) : 8663-XS
j: FPGA version (4 characters) : 0152


Please post your units response to this command if you wire up the management interface. I'd like to see what range of firmware/hardware versions are out there.
INV;
INV=GPS STAR 4+,015880,1508,01,015881,0149,14042010,0010,8663-XS,0152;


Thanks. Looks like same firmware, hardware, and FPGA versions.

BTW - the Alarm 9 should go away after some time. My units is finally showing no alarms, holdover performance status = match specification, and atdc status = activated. It took about 2 days after my powering it back up to reach that state.
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #116 on: August 28, 2015, 01:32:52 pm »
Ed - as requested - here is a longer Timelab capture for the Huawei. It stopped a bit earlier than I wanted, but I couldn't figure out how to extend the capture.

Reading the specs on this unit, I think my measurement set-up is not sufficient to really show what this GPSDO is capable of. It would be great if someone with something better than a 53131A counter could capture some data on this.

Yes, I think you're right.  In your earlier graphs you could see that the BG7TBL unit was flattening out in the low e-12 range while it wasn't clear where the Lucent and Oscilloquartz units were going.  Now we know that your counter's performance has merged with what I call the 'GPS line'.  It's the approximate performance limit of any GPSDO.  Early in the 'economical frequency standard' thread I think I had it on one of my graphs.

Let me see now, so far you've got a counter that's good enough for all normal uses and *three* GPSDOs and now you're complaining that your counter isn't good enough.  Moto, you're a Time-Nut!   ;D

Ed

I am some kind of nut, that's for sure.
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #117 on: September 06, 2015, 04:11:37 am »
I was asked on the other thread for details on the RS232 mod to the Huawei/Star4+ module. It is really trivial if you will just read the manual that usagi linked, but I did put some notes and a few pictures up for the poster in the other thread. Here is a link to that in case it is helpful to anyone here:

http://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/255/
 
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Offline neopticus

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Re: bg7tbl gpsdo master reference
« Reply #118 on: September 13, 2015, 11:42:25 pm »
Hi guys/gals,

since the Huawei/Star4+ board (with LEA-5T GPS chip) is not available anymore from eBay sellers, I looked into alternatives. I know, the frequency stability between different bg7tbl variants is unsignificant for normal uses and thus any board should do. However I won't be able to set outdoor antenna and that's why I was interested mainly on the Huawei-variant.

Now, LEA-5T is discontinued but there's a new chip, LEA-6T available.

There are two vendors selling evaluation boards:
http://shop.sysmocom.de/products/osmo-lea6t-gps
and
http://www.csgshop.com/product.php?id_product=127

For 181 EUR and 147 USD, they are bit expensive. Osmocom one seems more documented (it has even it's full schematics and board layout available as Git repository!).  They also have USB connectivity. However they do lack OCXO.

What do you think, how hard would it be to bypass the GPS chip on these other bg7tbl variants and hook the ref board output there instead? 

Alternatively one could start making these add-on boards too. The chips are quite expensive if bought separately (134 euros(!) in their web shop), but in quantities > 10 less than 50 eur/chip.

 

Offline usagi

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Re: bg7tbl gpsdo master reference
« Reply #119 on: September 14, 2015, 12:10:23 am »
without ocxo i don't think they will generate much interest for those looking for a precision frequency reference. especially not at that price while surplus gpsdo with ocxo are still widely available.
« Last Edit: September 14, 2015, 12:12:06 am by usagi »
 

Offline neopticus

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Re: bg7tbl gpsdo master reference
« Reply #120 on: September 14, 2015, 12:54:33 am »
What GPSDO would you recommend for indoor use?  I remember someone complaining about the reception of Trimble variant earlier, but otherwise that would have been my 2nd choice.

BTW. How does the Jupiter chip in James Miller's GPSDO
(http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm ) compare to Trimble and Huawei boards in this regard?

 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #121 on: September 14, 2015, 01:10:13 am »
What GPSDO would you recommend for indoor use?  I remember someone complaining about the reception of Trimble variant earlier, but otherwise that would have been my 2nd choice.

BTW. How does the Jupiter chip in James Miller's GPSDO
(http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm ) compare to Trimble and Huawei boards in this regard?

I think the BG7TBL 2014-12-09. It has a u-blox chip with good sensitivity, and should work fine if you just want a reference and don't care about software to monitor its status or the small frequency error.

That said, the operation indoors may be a bit iffy, and it will definitely hurt the accuracy of the time signal (but accuracy will still be fine if you just want a frequency reference). I just hooked up a u-blox 7th gen chip as part of a project I am doing. It is syncing 4-5 satellites sitting in a window, but was struggling a few feet back from the window. So just be aware that indoor operation may or may not work.
 

Online edpalmer42

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Re: bg7tbl gpsdo master reference
« Reply #122 on: September 14, 2015, 02:23:02 am »
You need to be more specific than just saying 'indoors'.  If you're on the top floor of a wood-framed building with ordinary shingles, you'll probably be fine.  If you've got six stories above you or a steel roof, you'll have to find a window that preferably faces towards the equator.

The Jupiter boards, like all older boards, are a bit deaf by modern standards.  If you've got a good antenna in a good location an older board will do fine.  If your antenna system is less than optimum, an older board could have problems or you might have to add an in-line amplifier.

Ed
 

Offline neopticus

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Re: bg7tbl gpsdo master reference
« Reply #123 on: September 14, 2015, 03:10:58 am »
Ed and Motocoder, thanks for your advice.

I'm living in a 4 story building (my apartment in 3rd story). It's an old apartment made mostly of bricks, so not so much steel&concrete here I think, except for the roof which is in fact steel..   :palm:  I might be able to setup the antenna outside facing the western window, but even then there's another building blocking the horizon, so there would be a cone of unobstructed sky approximately 45 deg vertically and 170 deg sideways.

My main use case would be to check the calibration of high stability OCXOs in my equipment, but in the future the go-to frequency standard at my lab would be rubidium anyway (that would be then checked every 1-2 months with GPSDO).

As suggested by motocoder, I think I'll settle for the 2014-12-09 variant then, as it seems to be the most sensitive of the GPSDOs available currently (unless the guy from 168electronics comes to his senses and starts selling his stock of Star4+ boards (190 left!) :wtf: ).

Most eBay vendors send items with the hockey puck (patch?) type antenna, but I think the cone / half-sphere shaped (helical?) antenna is recommended for time measurements. Have you in practice seen much difference in reception with these?
« Last Edit: September 14, 2015, 03:22:59 am by neopticus »
 

Offline motocoder

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Re: bg7tbl gpsdo master reference
« Reply #124 on: September 14, 2015, 04:08:23 am »
Ed and Motocoder, thanks for your advice.

I'm living in a 4 story building (my apartment in 3rd story). It's an old apartment made mostly of bricks, so not so much steel&concrete here I think, except for the roof which is in fact steel..   :palm:  I might be able to setup the antenna outside facing the western window, but even then there's another building blocking the horizon, so there would be a cone of unobstructed sky approximately 45 deg vertically and 170 deg sideways.

My main use case would be to check the calibration of high stability OCXOs in my equipment, but in the future the go-to frequency standard at my lab would be rubidium anyway (that would be then checked every 1-2 months with GPSDO).

As suggested by motocoder, I think I'll settle for the 2014-12-09 variant then, as it seems to be the most sensitive of the GPSDOs available currently (unless the guy from 168electronics comes to his senses and starts selling his stock of Star4+ boards (190 left!) :wtf: ).

Most eBay vendors send items with the hockey puck (patch?) type antenna, but I think the cone / half-sphere shaped (helical?) antenna is recommended for time measurements. Have you in practice seen much difference in reception with these?

I don't think the antenna is going to make a difference indoors. I'd start with the antenna that comes with the unit and save your money unless that's not working out.
 


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