[time-nuts] SR620 calibration

Douglas H Reed n0nas at amsat.org
Sun Feb 27 21:04:59 UTC 2011


Regarding the SR620 counters, I must have missed something.... It
seems to me that SRS is providing about as much support as Tek or
Agilent. All three offer PDF manuals and repair service. I doubt any
of them have free telephone repair support for out-of-warranty
products.

I did a Google search for "stanford research sr620 manual pdf" and it
returned a number of sites, including SRS and NASA, that had the SR620
manual available for free download in PDF format. I had looked for
that manual several years ago and found it then too. I did a quick
compare against the paper copy of the manual and it seems to be
similar although I will not say exactly the same since I didn't look
that close.

Since the manual has full directions for using the counter and for
doing calibration, I don't understand the comments that SRS doesn't
support the product and make the info available. The schematics are
not included in the PDF manual but that is true of most electronic
products. I expect my paper manual has them although I haven't
checked.

Regarding the cost of repairs, I don't care what company you talk to,
they are ALL too expensive for me. But since I didn't buy the
equipment new with a warranty I don't see where that is their problem.
I bought my car out of warranty and I don't expect the dealer to do
repairs for cheap. I have several pieces of test equipment that were
labeled "Not Economical To Repair." That is why they were in the scrap
bin. But they work good enough for me to use as long as I can live
with the fault.

I do like the counter even though I've never used any of the advanced
features it has. My only complaint was the 10^-6 accuracy of the TXCO
reference oscillator but since I can calibrate it at will and can use
my Z3801A as an external reference, I can live with that. Somewhere
along the line I need to do some research or get one of the gurus on
the reflector to explain how to use the SR620 for doing Allen variance
and other quality checks of the various GPSDO, rubidium, and OCXO
oscillators I've collected in recent years. That is about the most
advanced feature I need from the SR620.

I probably don't qualify as a real time-nut since my main interest is
to get my 10GHz station within a few hundred Hz of 10368.100 MHz. A
few parts in 10^-11 is good enough for that..... And I would like to
compare my various reference oscillators just to verify they are
working as well as can be expected. But that doesn't make me a REAL
time-nut.... :-)

I don't intend to rekindle the previous discussion, I just don't
understand the negative comments. I have several SR620 counters and
for a 1GHz counter I think they are pretty good. For higher
measurements I got lucky on eBay purchasing an EIP 25B counter that
seems almost new. I didn't get as lucky with the HP 5340A I bought
first. Expensive and unobtainable mixer parts make the 5340A
unrepairable.....

I do enjoy the technical discussions on the list. I particularly liked
the discussion about rejuvenating a rubidium lamp. The N4IQT web page
mentions the procedure but the time-nuts discussion provides a lot
more detail. That should be added to a web page somewhere along with
long term measurements of the results to indicate how the fix is
holding. I'm sure there are a lot of people who would be interested in
extending the life of their old rubidium oscillator. Having that info
would certainly make me sleep better if buying a surplus rubidium on
eBay.....

73, Doug Reed, N0NAS.



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