GPS frequency standard

[John Larkin]

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

 

[Don Bowey]

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

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

 

[James Arthur]

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

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:

http://www.rt66.com/~shera/index_fs.htm

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

 

[David L. Jones]

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?

My Stanford Research FS725 Rubidium standard allows connection of any
1pps external GPS reference, that's a pretty cheap, simple, and
powerful combination.
http://www.thinksrs.com/products/FS725.htm

Dave

 

[Robert Scott]

...many GPS modules have a one-pulse-per-second
output. Brooks Shera made a standard based on such a device..

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

 

[[email protected]]

My Stanford Research FS725 Rubidium standard allows connection of any
1pps external GPS reference, that's a pretty cheap, simple, and
powerful combination.
http://www.thinksrs.com/products/FS725.htm

Get a load of that 60Hz spike in the phase noise plot.
http://www.thinksrs.com/assets/instr/FS725/FS725_diagLG.gif

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

 

[John Larkin]

Get a load of that 60Hz spike in the phase noise plot.
http://www.thinksrs.com/assets/instr/FS725/FS725_diagLG.gif

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

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

 

[[email protected]]

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.

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.

http://www.stanford.edu/dept/news/pr/01/microdevices613.html

 

[Dr. Anton T. Squeegee]

[email protected] (known to some as John
Larkin) scribed...

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?

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.

 

[[email protected]]

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.

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

 

[John Larkin]

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...

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

 

[David L. Jones]

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.

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

 

[David L. Jones]

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.

http://www.stanford.edu/dept/news/pr/01/microdevices613.html

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

Dave

 

[ChrisQuayle]

[email protected] (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.

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

 

[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

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

 

[David L. Jones]

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.

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

 

[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

I use TAC32 software for this purpose.
http://www.cnssys.com/Tac32/

Dave

 

[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

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