Electronics > Metrology

Cheap GPSDO Buying Help 2024?

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Hi, gang,

My "unusual and obscure" BG7TBL GPSDO variant (5-8 years old) has developed a heat-related intermittency issue, and if I can't fix it, I'm in the market for a cheap GPSDO. I am already in a bit over my head, so there's that...

Compared to many Super Metrologists, my needs are ridiculously minimal. I use the GPSDO to discipline a frequency counter that, to date, has never needed to count above 100 MHz. In fact, without a prescaler it CAN'T count above 100 MHz. :)  I simply need to corral that device to an accuracy level of about "1 Hz in 50 MHz," which isn't overly special. I also have a spectrum analyzer that has a 10-MHz ref input, so when I build a distribution amp, that thing can play along, too.

My now-ailing unit has two 10-MHz outputs, one sine, one square. When it was working I successfully connected it to my venerable 5328A counter using both outputs, but I'm not sure whether a sine wave reference is "better" than a square.

Does it matter to the general variety of home lab devices?

I ask because I have been seeing some inexpensive GPSDOs (and OCXOs) on eBay for $40-$80. They seem to put out square-wave signals at 10 MHz, so if I need sine -- or want sine -- that might be a problem.

I learned to use Lady Heather to check in on my now-ailing GPSDO, so I don't know whether these inexpensive units can "speak to Lady Heather." I don't use the GPS time-keeping function from the software, etc, I just use it to confirm that My unit is seeing a bunch of satellites and that the ref output is locked." For now, perhaps forever, the rest of the info is just noise.

Can these cheapie GPSDOs "indicate lock," etc, or would I be missing out on necessary functionality, even for my minimal needs, if I don't get a unit that can speak Heather?

Can anyone offer advice on which cheapie units they have had success with, etc?

I appreciate your input,

Kirk, NT0Z

P.S. I SHOULD just bite the bullet and buy a Bodnar GPSDO and be done with it, but I'm trying to buy other goodies, too, so saving money is key...

I bought two GPSDO. The first was a cheapy 10MHz only from ebay; it works fine (for my needs, at any rate, which seem similar to yours).


Then I bought a Leo Bodnar that would do 10MHz and 96kHz on two separate outputs. A square wave output makes it easier for other equipment to lock accurately because most PLLs operate on a square wave internally. The cheapy GPSDO indicates when it has achieved lock (takes at least ten minutes), albeit not terribly intuitively. For best results, a GPSDO should be left permanently powered, so that is arguably unimportant. It is, after all, a crystal oscillator, and needs to settle. Something that did surprise me was that my oscilloscope initially refused to lock to the Leo Bodnar, yet locked happily to the cheapy. It turned out that the oscilloscope's Ref. In didn't terminate the cable and reflections were upsetting the square wave. A through termination solved that problem.

A distribution amplifier is the proper way to feed a number of destinations. But it's clear that some devices expect you to loop through. Like you, I have an RF oscillator that will lock to a 10MHz signal. Haven't yet tried it with a square wave.

No idea what Lady Heather is.

for such application , I use  a well isolated OCXO in Styrofoam , and do adjust it against gpsdo once in a while ( usually twice per year , or less )
the cheap one  - https://www.ebay.com/itm/266588217507  (it AC CUT)
it constantly ON , no any movement or reposition,   (gravity affect oscillation freq)   the result after  6-8 month like:  9.99999999XX Mhz
sufficient for 8 digit counter .....

recently got this one - no clue how well it work

so maybe ocxo approach , with some periodic sync, will work for you as well  ...

Buildd one from here https://www.eevblog.com/forum/projects/budget-gpsdo-a-work-in-progress/


for someone who not much familiar with  coding ..etc  . it a challenge


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