[time-nuts] Surplus Guidelines, was: Rubidium Standard

David Forbes dforbes at dakotacom.net
Sun Dec 10 16:39:40 EST 2006


I'm no expert at these devices, but here's what I've learned in the last year:

The Ball/Efratom FRK is the oldest design that's commonly available. 
They work, but are likely to be out of range and may have little life 
left in the physics package. Old-fashioned thru-hole PC boards, easy 
to work on. The manual is available on the web as a free PDF file.

The Ball/Efratom FRS comes in several flavors: A, B, C, N etc. It's a 
more modern packaging of the basic FRK design, but is very tightly 
packed in the box so is harder to work on. The stability specs aren't 
real good, either. The manual for these is also free on the web. Look 
for a recent date code - I think they were manufactured up until 10 
years ago or so.

The Datum/Symmetricom LPRO is a newer design and microprocessor 
controlled. Probably a good investment if it's recently manufactured.

The SRS PRS-10 is a very modern, microprocessor controlled version 
with a superior physics package and the ability to train onto a 
GPS-provided 1PPS signal. They sell for way more than the others, for 
good reason - they're designed to last for several decades.

Tom Van Baak has compared the stability of some of these devices... 
see the chart at the bottom of the page.

There are also some OEM modules that appear on ebay in quantity, 
which have an L shape to them. I haven't seen anyone post manuals for 
these, so they may be hard to debug.

You will also find packaged Rb units with front panel, power supply, 
backup batteries etc. They seem to sell for twice as much as the raw 
units. These will contain either an FRK or FRS unit inside, typically.

The HP 5065A has a much higher quality physics package than Efratom's 
units, from what I can discern. Which does you no good if it's worn 
out! They tend to be at least 25 years old and are highly 
questionable as an investment at that age.

>Second, since just about any of these type items on eBay are sold 'as-is',
>what is a reasonable price for some of these things? Prices seem to vary
>with no rhyme or reason. I would like to get a Rubidium standard one day,
>but I honestly don't know what a fair price would be for some that I have

If it works, a couple hundred dollars for a used FRS or FRK is 
reasonable. I picked up a never-used FRS-N unit for $300 recently. 
There was a batch of them that sold with steadily decreasing prices 
from $500 down to the $200 initial bid as the market (such as it is) 
got saturated.


--David Forbes, Tucson, AZ

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