[Premium-Rx] use of precision time base

[John Miles]

> 	Telcom grade rubidiums do tend to have less good short term
> stability and phase noise than the best of quartz frequency standards,
> so if those parameters are critical using a GPSDO based on a high
> quality quartz oscillator may give better performance and may well have
> plenty good enough short term holdover performance in the absence of GPS
> to satisfy most needs (at least if there is a UPS powering the unit so
> one is not dealing with a power outage and  cooling of the crystal).

That seems to be true, all right.  I recently compared my Thunderbolt with
one of the surplus Datum 9390 rubidium GPS standards that have been selling
on eBay lately.  Phase-noise plot here:
http://www.thegleam.com/ke5fx/compare.gif

The moral is, if you are going to drive a high-quality receiver or spectrum
analyzer, don't start with an unmodified Datum.  The FRS-C isn't that clean
by itself, and they somehow managed to make it even noisier by the time the
signal reaches the rear-panel 10 MHz output.

It actually makes sense to use a GPS-disciplined rubidium to discipline a
high-quality quartz OCXO.

-- john, KE5FX