[time-nuts] Surplus Symmetricom SA.22c data

Skip Withrow skip.withrow at gmail.com
Tue Nov 28 15:10:33 EST 2017

Hello Time-Nuts,

I recently characterized a lot of 29 used (surplus telecom)
Symmetricom SA.22C oscillators. These units never left the U.S. and I
removed them from the original boards.  I have attached a JPG of the
plotted results.  I also have a PDF scan, but it is too big to attach.

Basically, it looks like there is a bias for the oscillators being a
bit fast.  I think this correlates very well with the data that has
been published regarding helium permeation of the Rb gas cell
(http://freqelec.com/space/ieee_perfrmnc_qz_rb_space.pdf).  Most of
the oscillators are 2011 manufacture and have probably reached
equilibrium, it would be interesting to plot the data versus date code
for a range of oscillators less than five years old.

One question is - what about those slow units? - where did they start
out, and are there other things going on?

I think Corby has done some great work with his HP5065.  And recently
has shown his efforts to enclose the Rb cell and purge it with dry
nitrogen (is it He free?).  My thinking is that it should be pulled to
about 10 torr vacuum (about the same as the Rb cell pressure) to
create a He equilibrium to minimize aging.  I'm sure there are lots of
thoughts on both sides.

My reasoning is that for an oscillator that ages towards fast at
atmospheric pressure, and ages towards slow in space - there should be
some pressure that aging would be minimized.  Whether this is the case
for the 5065 is also a good question.

The good news regarding the SA.22c lot is that the DDS can be set to
put the oscillators back on frequency such that temperature, voltage,
and retrace dominate the frequency error.

Skip Withrow
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