[time-nuts] Symmetricom SA.22c rubidium oscillator information

Skip Withrow skip.withrow at gmail.com
Wed Feb 4 22:38:39 UTC 2015


Hello Time-Nuts,

I have been playing with some Symmetricom SA.22c rubidium oscillators and
wanted to pass on some of the interesting information that I have found.
RDR Electronics has a large number of these units in stock.

1. These oscillators are pulls from telecom cards and are 15MHz when
pulled.  The ACMOS output can be changed in frequency to any value equal to
60MHz/2N where N=1 to 65536.  We have been changing them to 10MHz when
testing.

2. There is a 1pps output that is off in the pulled oscillator.  During
testing we turn the 1pps on.  However, in the startup header it still
reports as off, but it IS on.

3. The startup header reports the correct values for the xtal (60MHz),
ACMOS (programmed value), and SINE (10MHz) outputs.  However, if the 'i'
command is later used these values are all wrong, there appears to be a bug
in the software.  Perhaps a hex to decimal oops, or something related.

4.There is an internal TIC (!) that can be read using the 'j' command.  It
has 16.7ns resolution.  The second input is the 1pps input pin (pin 15).
Over one second this is 1.67x10E-8, but sampling over longer intervals
gives correspondingly higher resolution.  It reads out in hex and seems to
work well.  There is also digital frequency control via the 'f' command
(2x10E-12 resolution).  So, with some software that can read and write a
serial port a GPSDRO wouldn't be too hard.

5. There is also analog EFC if desired.

6. The SA.22c User Manual and three pictures of the internals have been
downloaded to Didier's website.  They will be available for download once
they have been taken out of the upload area.

7. The Symmetricom X72 rubidium oscillator (smaller, and with 10-32V input)
is a close cousin to the SA.22c, at least from a user software perspective.

Hope this information helps for anyone that might have one of these, or is
contemplating using one.

Regards,
Skip Withrow



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