[time-nuts] Z3801 misbehaving

Charles Steinmetz csteinmetz at yandex.com
Tue Feb 2 14:06:38 EST 2016


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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