[time-nuts] Newbie question - what use is a Ruby?
Murray.Greenman at rakon.com
Mon Oct 5 18:12:01 UTC 2009
There are several uses for a Rb unit (even if you already have a GPSDO).
1. The Rb unit is very portable, and is on frequency from cold in 5
minutes. Great for tests away from home. Easily battery operated. No GPS
antenna required either!
2. With fast warm-up, they are ideal as a reference for gear you don't
use too often, and can't justify the power consumption (or added space)
of a GPSDO and its backup supply, which must run continuously.
3. Some units (such as the FEI FE-5650A and FE-5680A) are frequency
programmable, and so you can use them as a stable signal generator or
(if you're a Radio Amateur) as an Exciter for experiments. I have
software which can transmit an on/off or frequency shifted pattern for
4. They are a handy adjunct to the GPSDO. Use the latter to calibrate
the former, and then you've a reference even if GPS is unavailable. The
Rb units also have very good short-term stability.
5. If you are interested in making phase noise or frequency measurements
requiring a mix-down technique, the programmability of the FEI units is
very useful. Phase noise is good enough for most applications.
I have two units (FE-5650A and FE-5680A), from China. They started life
providing only 1pps (1Hz) and required reasonably simple modification to
provide 1kHz to 15MHz operation in ~10mHz steps. When thus modified, the
output level is about +9dBm. The units use a 50.255MHz oscillator in the
physics package, and this acts as reference for a built-in DDS
synthesizer, hence the frequency flexibility.
1. You can have any frequency you like, but only one with sub-ppb
accuracy (because of the DDS step size).
2. The power consumption (not that it's as high as the GPSDO).
3. Ageing, and the need for occasional calibration.
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