[time-nuts] Re: Is this bad OCXO behavior?

[Magnus Danielson]

Hi,

As you run the OCXO without the lock to the maser, what does it do then?

Can you probe the input before the loop?

The EFC Voltage is a consequence of the loop action, so sorting out what 
is a oscillator thing and what is sourced by other things becomes much 
easier by opening up the loop and measure things separately.

Cheers,
Magnus

On 2022-02-06 03:28, Skip Withrow wrote:
> 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
>
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