[DSP-10] GPS control

[Bob Larkin]

Hi All,

I am not sure of the thread on this one, but I would like to report the
setup at my station for frequency control. It is simple, but does the job
for me.

The basic setup is a 10 MHz osc using ordinary cold-weld sealed crystal.
This is phase-locked to GPS 1-second pulses with a Shera controller. Beb,
W7SLB built the oscillator and the fancy part is his double oven that
controls the temperature. It has a varactor for frequency control, but
otherwise is regular stuff.

With N=3 in the Shera controller, the the random variation in frequency is a
few parts in 10^10 (10 to the tenth power). This is better than the phase
modulation on most (interesting) propagation paths and so will not be the
limiting factor in weak-signal communication.

I use this oscillator for the station standard and phase lock various items
to it for operation up to 10 GHz.

Note that when you use the Shera controller, your frequency will, on the
average, be exact (the same as NIST). The frequency errors are both plus and
minus from this "correct" value. This is what "phase-lock" does for you.

I like the GPS-locked oscillator as it is self checking. A Rb oscillator is
very adequate for weak signal use, but if something goes wrong and there is
an error, it doesn't tell you about it. You still need the external checking
capability to be sure (GPS, WWVB, Loran-C).

Use whatever you can get ahold of, but holding your frequency to a part in
10^9, or better, really enhances the weak-signal capabilities. It also
allows you to see a lot about propagation paths to see what is happening.

73,
Bob  W7PUA