Test Equipment Anonymous

I finally ordered a basic GPS disciplined oscillator plus two distribution amplifiers in order to genlock the time and frequency sensitive test equipment to a common reference. This is actually a project I've had in mind in different versions for a long time and some of the test equipment in use dates back to the original idea.

Anyhow, I unpacked the GPS disciplined oscillator and the two distribution amplifiers and set them up on the bench in a temporary configuration for testing purposes over the next few days but I've got a location in mind for them for permanent installation when the time for that comes.





I got out a new power bar to accommodate the three power adapters. The way the plug prongs are oriented with respect to the rectangular adapter casing is annoying because they would block several adjacent sockets in a power strip. If they were rotated 90 degrees, you could space them closer together. Also, there is such a thing as too bright when it comes to indicator LEDs. These are painful to look at when you're trying to see if the middle one of the three is on.

The test jig is a Hewlett-Packard 5335A counter that has one of the high stability oven temperature controlled oscillator options on it to monitor the frequency of the GPSDO teed off to a Tektronix TDS640A to observe waveform. Either of those machines can provide a 50 ohm load termination so no external terminator was needed to maintain matched impedance throughout the entire system. It's going to be interesting to see how close the counter and GPSDO are to each other or if there's a significant discrepancy between the 10 MHz output of the GPS disciplined oscillator if it can lock up and stabilize, and what the counter claims the frequency of the output is.

The first test was to patch the test jig into the 10 MHz output of the GPS disciplined oscillator and verify it was working. It was initially off by about 26 Hz according to the 5335A until the lamp indicating GNSS lock came on and the oscillator settled in - it settled in fairly quickly and it was only out by a cycle with respect to the counter when I started taking pictures. I was able to get this picture of the counter just as the GPSDO was still settling in:





The waveform matched what the specifications of the GPSDO said to expect so it was time to move the connection feeding the test equipment over to one of the distribution amplifier outputs and connect the distribution amplifiers.



When I bought the equipment, I had thoughts of using a tee connector to effectively Y cord the output of the GPSDO to feed both D/A inputs in parallel but with a fallback plan to temporarily daisy chain one D/A from the other if paralleling the two distribution amplifier inputs loaded down the GPSDO output and order a third distribution amplifier to act as a top level D/A to take the GPSDO output and feed it to the other two D/As. Luckily, this wasn't necessary. Connecting one distribution amplifier to the GPSDO and then adding the second one didn't cause any problems and didn't cause any shifts in output from the D/A to the test equipment.





The GPS disciplined oscillator got a GNSS lock and settled in very quickly and it and the HP 5335A are very close to each other. The original idea I had for genlocking the test equipment to a master reference was to use the 5335A's 10 MHz reference out as the timing source because it has the optional timebase I mentioned earlier. Given how close it is to the GPS disciplined oscillator, I'd have no problem with substituting it as the master clock source to one or both distribution amplifiers if the GPSDO ever runs into problems and I have to wait for a replacement to come in.

I also put up the scope's frequency measurement function:



It's interesting to note how much further out the frequency given the scope is compared to the counter so it'll be interesting to see if that improves by feeding a 10 MHz reference into the scope from either the GPSDO or the counter's reference out and then measuring the other to see if it tightens up similar to how the GPSDO and counter are.



Finally, here's a picture of the two tests that are going to run overnight (minus the scope - there's no need to run up the CRT hours unnecessarily since it's frequency stability I'm most interested in). The 8903B is still running and it's numbers haven't changed much so far. I did try toggling the the 80 kHz low pass filter on and off and it does appreciably lower the THD+N vs. the analyzer input wide open.

Nice rack(s)!

-Pat

25 CPS wrote: ↑Wed Nov 30, 2022 5:47 am I finally ordered a basic GPS disciplined oscillator plus two distribution amplifiers in order to genlock the time and frequency sensitive test equipment to a common reference. This is actually a project I've had in mind in different versions for a long time and some of the test equipment in use dates back to the original idea.
...
The first test was to patch the test jig into the 10 MHz output of the GPS disciplined oscillator and verify it was working. It was initially off by about 26 Hz according to the 5335A until the lamp indicating GNSS lock came on and the oscillator settled in - it settled in fairly quickly and it was only out by a cycle with respect to the counter when I started taking pictures. I was able to get this picture of the counter just as the GPSDO was still settling in:

Ah, you lucky person. Now you have an excuse to get an Agilent 53310A Modulation Domain Analyser a.k.a. Time Interval Analyser a.k.a. Frequency Microscope.

That can be set to have a 14 digit frequency display, and can plot a graph of frequency vs time so you can see the startup transients, and frequency noise. You also ought to be able to spot any 21ns "clock slipping" due to the uBlox 48MHz internal clock.

Over at https://www.eevblog.com/forum/testgear/ ... msg3194292 I show the startup transient of an HP10811 OCXO.

I've also used it to measure the lockin transient of the 198kHz frequency standard using an off-the-air receiver. It shows the slight overshoot of a perfectly damped response, and much more noise than the OCXO. I ought to post some pictures sometime.

I also ought to look at the output of my cheap uBlox GPS receiver.

That class of instrument has now been discontinued. I wonder if the new breed of statistical frequency counters can give the same information.

Welcome to the timenut club

Now that I'm stocked up on cables, and I swear I must be missing a few to have run out so quickly like that, the contest could begin. Yesterday evening, I started up the other frequency counter, the Hewlett Packard 5334B that sits on top of the 5335A and connected it up to another distribution amplifier output. This time I was quicker with the camera and caught it in the warmup period:



A disagreement during warmup is to be expected but what's going to be interesting is to see how the 5334B performs over time with its standard oscillator over the 5335A which has the Option 10 high stability temperature controlled oven oscillator.



After 25 minutes of running time, the count drifted up through 10 MHz on the 5334B meanwhile the 5335A has barely budged one count in the least significant digit.



This morning, the count being displayed had drifted higher but the 5335A is still within one count on the least significant digit from where it had settled in early on. Since the output signal from the GPSDO is a sine instead of a square wave which would have the predictable odd order harmonic content, I thought it might be interesting to take a look at what kind of harmonic content the sine has:





I fed another distribution amplifier output into the HP 3588A spectrum analyzer and applied some video averaging to make the harmonic products stand out a bit better from the noise floor.



The most recent picture is from this afternoon before I left to pick up the truck from having the winter wheels put on. The HP 5334B continues to drift. I've left both counters switched on. Based on the results so far, I don't think either the GPS disciplined oscillator and the 5335A have moved around much since the least significant digit has only varied by one count since the 5335A stabilized. That 5334B is the one I'm more curious about.

Buying the 5335A with the Option 10 high stability oscillator and using that as my primary counter was definitely an excellent decision based on how it's been performing so far. Comparing how the 5334B has been wandering around compared to the GPSDO and the 5335A is a pretty good example why locking equipment to the same master reference using whatever your best oscillator happens to be is beneficial in terms of improving consistency between equipment vs. each machine being out by however much its built in oscillator is compared to any other on the bench. That's something I want to check out as I do the full installation, take the 10 MHz reference out of each device that has one and see how it compares to the GPSDO just out of curiosity to see how all over the map all my equipment is.

What's that funny thin white thing sticking out the bottom of your analyzer ?

tautech wrote: ↑Thu Dec 01, 2022 11:55 pm What's that funny thin white thing sticking out the bottom of your analyzer ?

A digital dinosaur. We shall call it Rupert.

mnem


*EDITED to show context*

I added a new tag, frequency-references, and attached it to this topic.

mnementh wrote: ↑Fri Dec 02, 2022 1:15 am A digital dinosaur. We shall call it Rupert.

mnem

Welcome to the forum Rupert.

What's your speciality ?

mnementh wrote: ↑Fri Dec 02, 2022 1:15 am A digital dinosaur. We shall call it Rupert.

mnem

It even looks like him!

Rupert looks constipated. I think he needs coffee.

mnem

tautech wrote: ↑Fri Dec 02, 2022 2:48 am

mnementh wrote: ↑Fri Dec 02, 2022 1:15 am A digital dinosaur. We shall call it Rupert.

mnem

Welcome to the forum Rupert. What's your speciality ?

I drink TEA and I know things. It's what I do.

mnem

mnementh wrote: ↑Fri Dec 02, 2022 2:19 pm

tautech wrote: ↑Fri Dec 02, 2022 2:48 am

mnementh wrote: ↑Fri Dec 02, 2022 1:15 am A digital dinosaur. We shall call it Rupert.

mnem

Welcome to the forum Rupert. What's your speciality ?

I drink TEA and I know things. It's what I do.

mnem

Here is the Real, definitive, Rupert, who I believe is a very remote cousin of mine:

vk6zgo wrote: ↑Sat Dec 03, 2022 12:00 am

mnementh wrote: ↑Fri Dec 02, 2022 2:19 pm

tautech wrote: ↑Fri Dec 02, 2022 2:48 am
Welcome to the forum Rupert. What's your speciality ?

I drink TEA and I know things. It's what I do.

mnem

Here is the Real, definitive, Rupert, who I believe is a very remote cousin of mine:rupert.jpg

Let's hope you don't share the way he looks.

He's smiling the smile of a man satisfied with his life's work. Let's all hope we look like that someday.

mnem
My WAG: Rupert Neve?

Naaaahhh... it is Rupert Murdoch. I didn't know he could smile without a half-eaten puppy between his teeth.

tautech wrote: ↑Sat Dec 03, 2022 12:19 am

vk6zgo wrote: ↑Sat Dec 03, 2022 12:00 am

mnementh wrote: ↑Fri Dec 02, 2022 2:19 pm

I drink TEA and I know things. It's what I do.

mnem

Here is the Real, definitive, Rupert, who I believe is a very remote cousin of mine:rupert.jpg

Let's hope you don't share the way he looks.

Some mongrel has stolen all my mirrors & replaced them with portraits of Rupert Murdoch!

Crikey, the Welsh red dwagon has an Irish connection to the family, just how far does this connection run, lets all hope that there is no Leprechaun in the family or we'll be doomed.

https://www.youtube.com/watch?v=1eIkqE-38Rc

And I'll bet that 3 minute gag reel was better than all 8 fucking movies combined... *blerk*

mnem
*gets out his Wee Folk mallet to keep handy just in case*

For some strange reason, my Meinberg, after the last reboot (power outage) back on October 28, decided to spend 2 bleeping weeks to get in order, then all of a sudden reported: It has not swayed from this for what in recent memory (regarding its lock status) is a pretty long time, and still remains locked with what must be described as a very good eye to the sky: I did look at a 10MHz -capable used Trimble bit of kit the other day; which would have fulfilled my timing needs. Maybe something took notice...

Maybe it was having a tiff with Lady Heather and just took that long before they made up...

mnem

That particular lady has not been involved; having the benefit of a Meinberg packaged solution means I have some statistics tools available without further complication. The plot I posted is simply asking (SNMP) the receiver every 2 or 5 minutes (can't remember which) how many birds it sees and if any are good, and storing it in a database. (no, not some fancy timeseries or NoSQL junk, a real, slow, non-fancy 90s style RDBMS.) The graph is then drawn using gnuplot.

On timing, I had reason to speak to the Swedish distributor for Trimble today, as I have a sizable bunch of GPS receivers in my routers at work, but need antennas for them.

Of course these antennas have a 3/4" NP (don't know if taper or straight) thread combined with a 1" marine antenna mounting thread. I have a source (Völkel at least, but perhaps also Walter) for 3/4" NP thread dies, and European 3/4" steel pipe is about 0,4mm off in diameter from US 3/4 steel pipe, meaning I probably can use European pipe and cut NP threads, but there is a delay to that procedure and I have a nice REMS EVA BSPT set... Has anybody tried BSPT in NPT and how bad was it? Pressure tightness is not necessary here.

mansaxel wrote: ↑Mon Dec 05, 2022 7:30 pm That particular lady has not been involved; having the benefit of a Meinberg packaged solution means I have some statistics tools available without further complication. The plot I posted is simply asking (SNMP) the receiver every 2 or 5 minutes (can't remember which) how many birds it sees and if any are good, and storing it in a database. (no, not some fancy timeseries or NoSQL junk, a real, slow, non-fancy 90s style RDBMS.) The graph is then drawn using gnuplot.

On timing, I had reason to speak to the Swedish distributor for Trimble today, as I have a sizable bunch of GPS receivers in my routers at work, but need antennas for them.

Of course these antennas have a 3/4" NP (don't know if taper or straight) thread combined with a 1" marine antenna mounting thread. I have a source (Völkel at least, but perhaps also Walter) for 3/4" NP thread dies, and European 3/4" steel pipe is about 0,4mm off in diameter from US 3/4 steel pipe, meaning I probably can use European pipe and cut NP threads, but there is a delay to that procedure and I have a nice REMS EVA BSPT set... Has anybody tried BSPT in NPT and how bad was it? Pressure tightness is not necessary here.

11 TPI vs 11.5 TPI. They should wind together far enough to provide a reasonable mechanical join.
Can you get good spanners/wrenches onto both ?

tggzzz wrote: ↑Wed Nov 30, 2022 9:19 am Ah, you lucky person. Now you have an excuse to get an Agilent 53310A Modulation Domain Analyser a.k.a. Time Interval Analyser a.k.a. Frequency Microscope.

That can be set to have a 14 digit frequency display, and can plot a graph of frequency vs time so you can see the startup transients, and frequency noise. You also ought to be able to spot any 21ns "clock slipping" due to the uBlox 48MHz internal clock.

Over at https://www.eevblog.com/forum/testgear/ ... msg3194292 I show the startup transient of an HP10811 OCXO.

I've also used it to measure the lockin transient of the 198kHz frequency standard using an off-the-air receiver. It shows the slight overshoot of a perfectly damped response, and much more noise than the OCXO. I ought to post some pictures sometime.

I also ought to look at the output of my cheap uBlox GPS receiver.

That class of instrument has now been discontinued. I wonder if the new breed of statistical frequency counters can give the same information.

Welcome to the timenut club

One of the Modulation Domain Analyzers is on the shopping list if I come across one for a reasonable price. Maybe one day.

Anyhow, the counters are still on since I figured I might as well let this experiment run while I wait to have time to do the proper installation of the GPSDO and distribution amplifiers. The 5335A has not budged at all but the 5334B still wanders up and down a little bit, probably being affected by the ambient temperature swings in my basement workshop. The Option 10 oven temperature controlled oscillator is definitely the way to go when buying one of these counters, all else being equal.

The big problem, right now, is going to be getting the time to do much more with this before the holidays are over courtesy of a very heavy work schedule.

25 CPS wrote: ↑Sun Dec 11, 2022 1:21 am One of the Modulation Domain Analyzers is on the shopping list if I come across one for a reasonable price. Maybe one day.

Anyhow, the counters are still on since I figured I might as well let this experiment run while I wait to have time to do the proper installation of the GPSDO and distribution amplifiers. The 5335A has not budged at all but the 5334B still wanders up and down a little bit, probably being affected by the ambient temperature swings in my basement workshop. The Option 10 oven temperature controlled oscillator is definitely the way to go when buying one of these counters, all else being equal.

I too waited, and my patience was rewarded.

My first MDA was an HP5371 from PPAuctions. I very quickly scrapped it, but kept the 10811 OCXO.

I made a reference oscillator from that 10811 by putting it in a case with a PSU consisting of a bridge rectifier (to avoid polarity infelicities), a capacitance multiplier (to reduce any ripple), the 723 regulated supply (defined the the manual, has stable internal reference), and some RF inline filters.

Finally I tweaked the output frequency so it was the same as one derived from the LW Droitwich 198kHz standard - but with much less noise of course.

That reference oscillator is as good as the one in the Agilent 53310, unsurprisingly

Nice!, i have good experiance with those
if you like to upgrade to more sattelite standards..
here i made a nice video how to.
your GPSDO can do a lot more then advertised.

https://www.youtube.com/watch?v=eAdJSErqZOk

TonyAlbus wrote: ↑Sun Jan 15, 2023 8:35 pm Nice!, i have good experiance with those
if you like to upgrade to more sattelite standards..
here i made a nice video how to.
your GPSDO can do a lot more then advertised.

https://www.youtube.com/watch?v=eAdJSErqZOk

It’s good to see you here!

I’ll take a look at your video once I’m home from work and give it some thought since other capabilities of the GPSDO might change my thinking about where I want to permanently install it when I get to doing that. Hopefully that will be this weekend since the infection I’ve been fighting off is finally settling down nicely.