[time-nuts] Racal-Dana 1992 switches

Tom Duckworth tomduck at comcast.net
Wed Apr 2 16:03:00 EDT 2008


I have attached a PDF of two methods we used at XL Microwave for adjusting
the internal reference oscillators in our microwave counters. The second
method (digital) was used to calibrate the internal reference time base of a
70 GHz microwave counter with an accuracy of parts in E-11.

This digital method could be used to compare two GPSDOs, one to the other,
and would probably yield greater resolution than trying to use a phase
measurement on a counter due to jitter, internal noise, and stability issues
in the count chain. This method proved to be fast, simple, stable, and
superior to other methods we tried.

Hope this helps.

Tom Duckworth
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bill Hawkins
Sent: Friday, March 28, 2008 7:09 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Racal-Dana 1992 switches

Charles S. Osborne said, in part,

"Now the real question is... is there a clever way to make the Racal
1992 readout the difference in µHz between two GPS disciplined
oscillators? My only other counter, an HP5384A, is offscale at 10.000
000.000 MHz . I'm referencing the counter with one Lucent RFTG-m-XO and
clocking a Lucent RFTGm-II-XO. Things are working well enough to be
beyond my counter's ability to see any jitter. The Racal says nanosecond
time interval counter, so I bet there's a way to subtract and increase
the resolution similar to an HP53131?"

Haven't seen the answer on this list, so perhaps it occurred privately.

The Racal 1992 is able to read the phase error between two 10 MHz
signals (A and B) in degrees. I have done this with the outputs of two
3801s, which are the only pair of frequency sources that I have. This
would be sub-nanosecond accuracy except that the display shows 3-10
degrees of jitter (difference between two successive readings). This,
however, is only 10E-9. Most people on this list are investigating areas
at least two orders of magnitude lower.

I find that the phase method gives me comparative drift errors soon
enough. An hour gets you near 10E-12. Others require measurement
intervals much shorter than that, but the phase angle method is more
than adequate for time errors that humans will notice. A drift of one
second per year is on the order of 10E-8.

It all depends on your reason for pursuing accurate time/frequency

Bill Hawkins


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