[time-nuts] Making a HP 10811 better

Bob Camp lists at rtty.us
Mon Mar 29 21:09:46 UTC 2010


Hi

Thermal shifts from tip are a very real issue when you flip around OCXO's.
The acceleration is an instantaneous change. The thermal will have a time
constant out beyond 30 seconds. It's pretty easy to separate the two if you
have something that functions like a strip chart recorder. Stable 32 does
the job very nicely...

There is a second thermal issue related to just plain blowing a bunch of air
over the OCXO, compared to still air. That may or may not be significant
depending on just how well the 10811 is shielded in your pendulum. 

Bob 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Tom Van Baak
Sent: Monday, March 29, 2010 4:58 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Making a HP 10811 better

> Now if you really want some fun connect your OCXO to a
> one meter cable and let it swing like a pendulum clock. You
> should see some very nice sinusoidal FM as it goes back
> and forth. Devise some sort of mechanical, compressed air,
> or magnetic impulse system to keep it running like that all day.
> 
> /tvb

It works! http://www.leapsecond.com/pages/10811-g/

Bob, it would seem the frequency shifts in this swinging
10811 oscillator are all acceleration related and not due
to internal temperature variations, right? I could imagine
there are (longer time constant) thermal effects for a full
2g turn-over, but not with this short ~1 Hz period.

In fact you can see a slight, probably temperature gradient
related, frequency drift after a full 2g turn (I waited about
5 minutes after each turn):

http://www.leapsecond.com/pages/ocxo-2g/TBolt-2g-6axis.gif

/tvb


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