[time-nuts] GHz output from fe5680a

Tom Van Baak tvb at LeapSecond.com
Tue Jan 31 00:24:39 EST 2012


> hello everyone,
> 
> I'm just wondering if its possible to tap into the GHz output from the
> rubidium in the fe5680a.
> 
> many thanks
> 
> Chris

If I understand your question right...

Most rubidium frequency standards (and cesium for that matter)
do not actually output that frequency. I know in the popular press
they talk about the "precise vibrations of the cesium atom" or the
"precise frequency that they emit" but that's a metaphor and not
how they actually work. The atoms don't vibrate, they don't emit
a GHz frequency, and you don't count 9,192,631,770 of them to
make one second.

What typically happens is that electronics synthesizes an RF
(microwave) signal and continuously sweeps across a narrow
range of frequencies; the element (Rb or Cs or H) will respond
more or less depending on how correct the probe frequency is.
A servo then tries to keep the probe frequency centered on the
peak. These are all called "passive" standards.

The rare exception is the "active" hydrogen maser; where there
really is a live signal (1420+ MHz) coming out of the apparatus.

You may find these two papers helpful:

    Introduction to time and frequency metrology
    http://tf.nist.gov/general/pdf/1288.pdf

    Fundamentals of Time and Frequency
    http://tf.nist.gov/general/pdf/1498.pdf

/tvb





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