[time-nuts] getting a grip on 10811 drift (beginner-ish question)

[Bob Camp]

Hi

Sounds very normal to me.

The EFC voltage can be converted directly to a frequency change. There are
enough variants of the 10811 that checking what you have is probably the
best idea. A good guess is that it tunes 0.2 ppm over the full EFC range.

To check the OCXO - break the loop, hook up a counter and take the EFC to
each end of it's range. Lastly, ground the EFC. The three readings should
give you a good idea of the gross sensitivity of the 10811 you have. For a
more accurate number, step off the voltage in 1 volt steps and measure the
frequency at each step. 

Yes, you need a counter to do the measurement. It does not have to be
anything super fancy. It does need to be able to "see" 1x10^-8 at 10 MHz.
With a computing counter not to hard. With a conventional counter, you need
a gate time of 10 seconds or more. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Chris Howard
Sent: Monday, November 05, 2012 9:49 AM
To: Time Nuts
Subject: [time-nuts] getting a grip on 10811 drift (beginner-ish question)


I built a GPSDO using my own power supply,
a VE2ZAZ board, a Trimble Resolution T GPS
and a surplus  HP 10811 oscillator.


I'm having a bit of trouble with it.   I have it set up and
it locks ok and stays in lock so far.  But the recommended
long-term integration setting is not working for me.
I think it is about 3 hours.  At the end of every cycle
it does a control voltage adjustment, always in one direction.
If I understand it right, the oscillator is slowing and needs
an incremental bump downward of control voltage every time.

That seems like it is more than just long term drift.  But
I don't have my head around the quantities I'm looking at.

I can measure the control voltage change over time.  Can I convert that
into a frequency drift?  Or do I need to stop the voltage
adjustments and allow the drift to occur then do a measurement
of that directly somehow?

Is this type of behavior an indication of dire problems
with my 10811 oscillator?

Chris Howard
w0ep

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