[time-nuts] Is this bad OCXO behavior?

[Skip Withrow]

Hello Time-Nuts,

Well, hopefully many of you have read the saga of the Sigma Tau MHM-A1
restoration by now.

Seems like the next chapter has already begun.  Attached are two
graphs, one of the VCO EFC voltage, and one of the VCO supply voltage.
They cover about a six day period (logged once per hour).  As you can
see the EFC plot has several blips in it.  After two of the three
episodes there is an offset in the EFC voltage.

The second plot is the VCO supply voltage.  There does not appear to
be any spikes there that correlate to the EFC events.  You can see the
daily diurnal variations in the supply voltage as there is 2 ohms in
series with the supply before this point (and the bus supply has a
slight diurnal variation as well).

I know that OCXO's can have these types of jumps.  But I have to
believe that this is not a desired thing for a maser.

The two big questions I have are:

1. Should I consider replacing the oscillator?  It is an Austron 1120L
which is probably unobtainium.  However, there are probably lots of
SC-cut low phase noise units out there today that would beat the pants
off this unit.

2. Could it be a component other than the crystal?  Not that I want to
go tearing into the oscillator again, but if it was the varactor diode
or a capacitor I might be up to the challenge.  The problem is trying
to identify the faulty component.

Just wondering what the hive mind thinks.
Thanks,
Skip Withrow
-------------- next part --------------
A non-text attachment was scrubbed...
Name: VCO-EFC.pdf
Type: application/pdf
Size: 54927 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20220205/045556e1/attachment.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: VCO-Vcc.pdf
Type: application/pdf
Size: 56007 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20220205/045556e1/attachment-0001.pdf>