Joseph, 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 ID purposes. 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. Disadvantages? 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. Regards, Murray Greenman _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
