[time-nuts] Z3801 misbehaving

John Green wpxs472 at gmail.com
Tue Feb 2 22:16:48 EST 2016

 The OCXO has always been pretty warm to the touch. Except now, it is
barely warm.  I tried the antenna first with a card sized Symmetricon GPSDO
and it locked up OK. I have a small uBlox GPS that gives the signal levels
of the satellites it sees. I need to hook that up and check. The Antenna is
a Leica AT503 up 40 feet on a Rohn 25G tower. It is on top and seems to
have a pretty good view of the sky. It is fed 12 volts from a wall wart
power supply through a Pasternack bias Tee. I couldn't find any info on the
AT503 but I took it apart and the preamp has a 7808 voltage regulator in
it, so I think 12 volts should work alright. The cable is LMR400 from an
actual HP cable intended to work with GPS. I have a lot of checking to do
before I can narrow things down.

On Tue, Feb 2, 2016 at 1:06 PM, Charles Steinmetz <csteinmetz at yandex.com>

> John wrote:
> I am now thinking it may be an OCXO outer oven failure. It normally
>> runs quite warm. But now, it seems it may be body temperature or maybe a
>> little less.  The 10811 is different to a stock one but, is the outer oven
>> voltage the same? I would think the inner oven should keep it warm enough
>> to achieve lock and hold it. The outer oven is mostly to make the inner
>> oven's job easier.
> Typically, the outer oven of a DO 10811 is on a thermostat.  It receives
> power only when the OCXO is warming up from cold, and is switched off when
> the inner oven gets close to its operating temperature.  So, the outside of
> the OCXO package is warm during warmup from cold, then less warm during
> normal operation.  If the outer oven does not heat, for any reason, the
> inner oven will eventually (~30 min.) get the crystal to operating
> temperature and it will work normally after that.
> The symptoms you have described all suggest very strongly that something
> is wrong with the antenna feed to the 3801:
> --  bad antenna location (needs to be outdoors with a clear view of at
> least the southern half of the sky, assuming you are in the Northern
> hemisphere)
> --  bad antenna
> --  no DC power reaching antenna
> --  bad antenna cable
> --  bad antenna cable connector(s)
> It's possible something is wrong with the 3801, but if it worked properly
> when it was taken out of service, it is *much* more likely that the problem
> is one of the items listed above.
> Best regards,
> Charles
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