GPS frequency standard

It would be nice to have a primary frequency standard around here. We have a rubidium, but that's not technically primary, and we'd like to check it anyhow. And we do have a huge ole HP cesium, but you damn near need a PhD to operate it.

Has anybody used a GPS standard? Any comments or recommendations?

John

Reply to
John Larkin
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I don't have any hands-on with GPS used as a "traceable source" to a Primary Reference Frequency, but I know they are in wide use in Central Offices and Cell sites. I'm not aware of any tweaking requirements.

I imagine cost will depend on the holdover characteristics if the signal is lost. Applications I'm familiar with typically use two with an auto-switch.

If you have any Telco channels, such as DS1 or DDS, they, too, are traceable to a Stratum 1 clock and the signal can be used.

Don

Reply to
Don Bowey

Haven't used any, but many GPS modules have a one-pulse-per-second output. Brooks Shera made a standard based on such a device, with pieces-parts for sale:

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I once considered this, LORAN, WWVB, and OMEGA (now decommissioned) as signal sources; each has advantages, but if you've got line-of-sight, GPS is pretty sweet.

Best, James Arthur

Reply to
James Arthur

My Stanford Research FS725 Rubidium standard allows connection of any

1pps external GPS reference, that's a pretty cheap, simple, and powerful combination.
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Dave :)

Reply to
David L. Jones

But be careful! I tried to make something like that using a Sandpiper GPS module. I used the rising edge of the 1 PPS pulse output, but it appeared a little unstable. Then I found out that the rising edge was determined by some random firmware latency in the Sandpiper GPS. Fortunately the falling edge was hardware-determined and very stable. But the documentation on the received made no mention of this. I had to find out by trial and error. I suppose there may be some GPS receivers out there with 1PPS outputs where both edges have random firmware latency. Unless the makers went to the trouble to bring out the precise edge, it may not work. Ask for specs on maximum latency.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

Get a load of that 60Hz spike in the phase noise plot.

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It's a shame they don't use better line filtering in such a nice piece of equipment.

Reply to
maxfoo

We have an SRS ovenized SC-cut oscillator, clone of some old HP brick, which we rack mounted with some buffers. It's pretty good, with jitter of a few ps per second, and longterm stability in the 50 ppb/year sort of range. There's no 60 Hz, because we did the power supplies ourselves!

The temperature control loop is hilarious. It was made to work, but obviously by someone who didn't understand the dynamics.

SRS is strange; they make one of everything, sort of all over the place. The business model is to find some old, overpriced product and kill it. Probably a fun place to work.

John

Reply to
John Larkin

I always wondered why Stanford University has never sued SRS for the use of the name 'Stanford', like they did Sirenza Microdevices formly known as Stanford Microdevices.

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Reply to
maxfoo

In article , snipped-for-privacy@highNOTlandTHIStechnologyPART.com (known to some as John Larkin) scribed...

I've been using a retired HP Z3801 here for many moons. Great unit, makes a fine reference for my service monitor and anything else I may need 10MHz for.

They still turn up on greed-bay periodically, as do others. If you happen to get hold of a GPS-referenced clock, many of them have disciplined 10MHz outputs as well.

Happy hunting.

--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
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Reply to
Dr. Anton T. Squeegee

Did you attenuate the 60Hz below -150dBc/Hz? It is tough designing a notch that will attenuate 60Hz -150dB noise floor. just playing around with a twin-t notch in ltspice...

twin-t bandstop filter v1 1 0 ac 1 sin r1 1 2 26.52 c1 2 0 200u r2 2 3 26.52 c2 1 4 100u r3 4 0 13.26 c3 4 3 100u rload 3 0 1k .ac lin 800 40 80 .plot ac v(3) .end

Reply to
maxfoo

The best way to keep 60 Hz out of an oscillator is to not put it in to start. Then you don't have to filter it out.

John

Reply to
John Larkin

Yeah, would be a good place I recon. None of their gear is state of the art, mostly using garden variety parts, but they are cheap and functional. SRS gear makes a project budget stretch further which is a nice thing, hence I have fair bit of their stuff. We use plenty of their SR785 Dynamic Signal Analysers, a pretty good DSA and much cheaper than the Agilent equivalent which has been the industry standard for ever.

I like that they give you the full schematics and theory of operation for almost every bit of gear. Came in handy when we blew up the SR560 preamp front end which is pretty easy to do BTW.

Dave :)

Reply to
David L. Jones

Free gear would go a long way I'm sure? :->

Dave :)

Reply to
David L. Jones

I bought one of those on Ebay a few years ago for less than $200 and it's been powered up ever since. Got the correct antenna from an Ebayer in Korea. Came with software that lists status, drift and error etc. You can even set the cable length to compensate for the ns delay. Short term, there's quite a bit of instability, (relatively) but long term, they are very good and traceable to caesium at nbs. They do drop out of lock into holdover mode from time to time, but overall, an excellent piece of kit, fit and forget etc, at a fraction of the cost of the HP caesium box...

Chris

Reply to
ChrisQuayle

I have a DG535 delay generator. The schematic in the manual was obviously hand-drawn, with notes like "repeat this 4 times." Then there are faint scribbles like "try 22 pF here" and such.

John

Reply to
John Larkin

Hilarious! Guess they haven't updated that one in some time. The SRS tech manuals I have are a tad more professional than that. Proper CAD schematics, BOMs, overlays, theory of operation, calibration etc.

Dave :)

Reply to
David L. Jones

I use TAC32 software for this purpose.

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Dave :)

Reply to
David L. Jones

The 535 was their first product. The founder of SRS was an acquaintance of the founder of Berkley Nucleonics, and told him, over lunch as I recall, that he was going to start his own company and the first thing he was going to do is kill BNC's delay generators. And he pretty much did.

John

Reply to
John Larkin

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