GPS Devices -- Measure & analyze the period of the 1 PPS Output
Device ............... Std Dev (ns).... Range (max-min)(ns) ... Device ...... Notes
Navsync CW12 ......... 4 - 5 .......... 20 - 25 ............... GPS Rcvr .... 1,7
Motorola UT+ ......... 40 - 55 ........ 95 - 110 .............. GPS Rcvr .... 2,7
Rockwell Jupiter ..... 10 ............ 50 ................... GPS Rcvr .... 3,7
Motorola M12M ........ 10 - 15 ........ 40 - 60 ............... GPS Rcvr .... 7
Trimble Thunderbolt .. 0.4 - 0.5 ...... 2 - 4 ................. GPSDO ....... 6,8
HP Z3801A ............ 0.1 - 0.2 ...... < 1 ................... GPSDO ....... 6
HP Z3817A / CW12 ..... < 0.1 .......... < 1 ................... GPSDO ....... 4,6
Jackson Labs GPSTCXO . 0.3 - 0.4 ...... 2 - 3 ................. GPSDO ....... 6
NEC NWM-034241-201 ... 0.1 - 0.2 ...... < 2 ................... GPSDO ....... 5
Trimble UCCM ......... 0.09 - 0.11 .... < 1 ................... GPSDO ....... 5
Results are based on multiple runs of ~ 1000 measurements each.
Sawtooth correction has not been used for any of the GPS receivers. Where supported, it would reduce the numbers substantially.
All units were connected to the same antenna system.
Notes
1. Sawtooth correction not supported.
2. Most 'range' results were in this group, but there were a few at 20 - 30.
3. Only one test.
4. Requires external 1 PPS input. Equipped with E1938 oscillator.
5. Measurement made with Fluke PM6681.
6. Measurement made with HP 5370B.
7. Measurement made with HP 5372A.
8. Standard parameters.
9. Optimized parameters. (Not yet used in any tests)So you didn't get enough good info from the other thread you started:
https://www.eevblog.com/forum/testgear/what-frequency-standard-is-sufficient/ (https://www.eevblog.com/forum/testgear/what-frequency-standard-is-sufficient/)
:-//
but I'd like to see some similar measurements for some of the newer models. I have no intention of trying to buy one of everything!
but I'd like to see some similar measurements for some of the newer models. I have no intention of trying to buy one of everything!
Well, uhhh, I pretty much have at least one of each. I'm in the process of testing them all in the same config. Using a TAPR TICC clocked by a HP-5071A cesium beam oscillator. PPS goes to channel A and the 10 MHz divided down to 1PPS goes to channel B. GPSDOs are allowed to warm up for at least 24 hours.
You don't need to go to 20K sec. to characterize a GPSDO.
You don't need to go to 20K sec. to characterize a GPSDO.
Actually you should... a lot of GPSDOs seem to want to occasionally go a bit bonkers. If you are only looking at 1000 seconds of data, you can easily miss the shenanigans. And to be really safe make sure you include the time around 00:00 UTC (and particularly around the time-of-week rollover)... evil spirits like to come out an play around the witching hour.
I agree with you, but that's a never-ending chase. There will always be weird 'corner cases' where strange things happen.
I agree with you, but that's a never-ending chase. There will always be weird 'corner cases' where strange things happen.
Q&A red alert :scared: [Pseudo]random glitch fanboy identified. You know what will happen if such attitudes will sneak up on growing generation and logic/code ends up in vehicle software, banking, etc? I know you know but just preaching the other readers... :rant:
Oscilloquartz is part of Swatch ...
You don't need to go to 20K sec. to characterize a GPSDO. You know that if you average over a long enough time period, the frequency will be dead on. You can measure Allan Deviation, but they all resemble each other pretty closely - particularly at large tau values where they all converge due to the impact of GPS disciplining. The only place you'll see differences is in the central part of the graph where the OCXO and the disciplining parameters affect the graph.
You don't need to go to 20K sec. to characterize a GPSDO. You know that if you average over a long enough time period, the frequency will be dead on. You can measure Allan Deviation, but they all resemble each other pretty closely - particularly at large tau values where they all converge due to the impact of GPS disciplining. The only place you'll see differences is in the central part of the graph where the OCXO and the disciplining parameters affect the graph.
You're making the assumption that the GPSDO is operating correctly. The main reason for testing a device is to verify that it is operating correctly.
The assumption that probably should have been stated is that you've got lock, good satellite visibility and signal strength, completed survey, etc. You can't measure ADev or Std. Dev. until all the basics are covered. These steps alone will weed out most faults.
... an 18 hour test is just as arbitrary as a 1K (~17 min.) test. I'd rather do a few 1K runs on different days and times than one 20K test.
The assumption that probably should have been stated is that you've got lock, good satellite visibility and signal strength, completed survey, etc. You can't measure ADev or Std. Dev. until all the basics are covered. These steps alone will weed out most faults.
Most faults doesn't mean all faults. That's why you do the tests. (Especially since people on this forum seem to favor used equipment of unknown condition bought at bargain basement prices.)Quote... an 18 hour test is just as arbitrary as a 1K (~17 min.) test. I'd rather do a few 1K runs on different days and times than one 20K test.
It's not an either-or choice. It's just as easy to make a few 18 hr. runs on different days, and cover all your bases.
I originally posted this image in the wrong thread...
Here is an example of why you want to look at GPSDO data over extended periods of time. A 1000 second run would miss that big honkin' burst of crapitude.
Here is an example of why you want to look at GPSDO data over extended periods of time. A 1000 second run would miss that big honkin' burst of crapitude.Texaspyro, In real world terms, what is the significance of this "burst of crapitude"? Is this something that only affects the operation of a machine depending on the short term stability of the GPSDO signal? Or is this something that adds error to the long term accuracy of the GPSDO? I'm not very familiar with the concepts to work this out for myself.
Was the cause internal or external? Weird microwave oven or someone playing with a GPS blocker? Bad solder joint or logic error? Was it a one time event or will it repeat? How long are you going to continue the test? What have you proven?
Now you're just trolling.
You know as well as I do that this is a statistical rabbit hole that has no end. 'All faults'?? Good luck finding 'all faults'. Every user has to decide what level of performance is appropriate for their situation.
But if someone is even thinking that they might need to do 'a few 18 hr. runs' to 'cover all your bases', they won't be buying their hardware on fleabay because their corporate lawyers won't let them.
This isn't a professional time-nut forum. It's a bunch of hobbyists who think that GPSDOs and other time-nutty things might be interesting to play with. Telling them that they have to spend many hours making a single set of measurements is neither helpful nor correct. You might as well tell someone that's making a 555 led blinky that his test is a failure unless the frequency is correct to withing a milliHertz.
How can one test a GPSDO 'device under test' without a better one to compare it to?
How can one test a GPSDO 'device under test' without a better one to compare it to?
A comparison to a local atomic standard including a rubidium will reveal problems in the GPSDO disciplining.
A comparison to a local atomic standard including a rubidium will reveal problems in the GPSDO disciplining.
That depends upon the quality of the atomic standard and of the GPSDO. A lot of rubidiums (particularly surplus telecom ones) are worse than a lot of GPSDOs. The HP-5065A rubidium is an exception...
How can one test a GPSDO 'device under test' without a better one to compare it to?
Assuming you mean the output signals, you can't. You need to compare it to some higher-speced device. An HP-5071A with the high performance tube works fairly well. Or a maser.
You guys are so pessimistic!!
You guys are so pessimistic!!
Nope, we're time nuts. We want out shineys to be all shiney down to the atto-hertz.
You guys are so pessimistic!!
Nope, we're time nuts. We want out shineys to be all shiney down to the atto-hertz.
Yeah, I've noticed.... ;) I can't handle that. I start to get lightheaded when I go below 1e-13. ;D
You guys are so pessimistic!!
Nope, we're time nuts. We want our shineys to be all shiney down to the atto-hertz.