[time-nuts] Beginner's time reference

J. L. Trantham jltran at worldnet.att.net
Fri Dec 11 15:33:13 UTC 2009


Charl,

I am very new to this as well and I had similar goals you to yours.

In the end, all of these standards use a crystal oscillator.  It is just a
matter of what is doing the disciplining.  The Cesium Beam, Rubidium, and
GPS signals all discipline a crystal oscillator.  The quality of the signal
and the quality of the crystal oscillator ultimately determine the quality
of your 'standard'.

I agree with the comments about the lifespan of the Cesium and Rubidium
references and the 'crap shoot' of buying Cesium Beam standards from eBay.
However, it is fun to play with these and I have had good luck finding
'resuscitatable' equipment.  The only option for a primary, independent,
stand alone reference is a Cesium Beam or higher.  The rest are secondary
standards and must be calibrated against something else.

If you have a Cesium Beam and run it in the 'CS OFF' position, pumping the
tube down and leaving the crystal oscillator on continuously, you get pretty
amazing stability from just the crystal oscillator after it has been on for
a couple of months.  You can compare it to a GPSDO or you can turn on the
Cesium Beam (only when you need it) and be 'independent of the grid', so to
speak.

A GPSDO such as the TBolt gives you NIST linked accuracy and a clock that
you can set to GPS time or UTC time with adjustments for the time delay in
your antenna coax, etc., to get you as close as possible.  If your Cesium
Beam also has a clock, you can set it to match the GPSDO and watch the two
to see if it stays within a second per year with the 'CS OFF'.  However,
running a Cesium or Rubidium continuously will likely be expensive in the
long term.

In any event, this is a very addicting activity and has been the source of
great satisfaction except for my wife who thinks I have 'too much stuff'.

Good luck.

Joe




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