[time-nuts] Fwd: Re: Using a Racal 1992
Charles P. Steinmetz
charles_steinmetz at lavabit.com
Tue Dec 13 22:44:34 UTC 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,
Charles
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