[time-nuts] Fwd: Re: Using a Racal 1992

Charles P. Steinmetz charles_steinmetz at lavabit.com
Tue Dec 13 17:44:34 EST 2011

Chuck wrote:

>Small tweeks to the fine freq ... adjustment take several minutes to 
>take effect. Is the fine adjustment tweeking some parameter related 
>to the oven???

I doubt it, but I do not have actual knowledge of the inner 
workings.  I have found that the heat loss (I assume) through the 
open adjustment plug screw causes an error -- you can get them 
adjusted as closely as you can (in my experience, about 1E-9 with 
lots of hair-pulling) and they will sit there stably for as long as 
you want, then when you put the plug screw back in they drift several 
parts in e-9 or more over a period of 10-15 minutes and stabilize at 
a new value.

The good news is that the Racal oscillators in my 1992s are very 
stable long-term performers -- and significantly less 
position-sensitive than many others.  So, you don't have to adjust 
them very often.  The bad news is that getting them really, really 
close to the desired frequency is like herding cats.  Other than the 
flaky pushbuttons on some of them, I have found that 1992s are 
extremely dependable.  When a 9-digit counter will do, they are a 
great choice.  (Of course, as time/frequency nuts we quickly outgrow 
9-digit counters.  Doesn't every measurement require 12 digits 
referenced to an H-maser?)

I think it's been asked, and recently, but I haven't seen a positive 
response.  Does anybody have schematics for the Racal OCXOs they can 
make available?

Best regards,


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