From G3PLX:
Checking across the LW band, most of them seem to be some fraction of a Hz
off. On 162 there's one which is spot on, but another about 0.32Hz high. I
don;t know which is which, but certainly the lower of the two is spot on.
Closer to 198, there's a German one on 207 that's spot on. The worst one is
the Irish one on 252, which is 1.73Hz low.
When I say spot on, I mean that I can't see any significant phase rotation
over a few minutes, relative to the 1Hz output of my GPS, so that's within a
few mHz or so.
The system I use relies on the RF harmonics of the rising edge of the 1Hz
reference output of my GPS, which gives a click when fed straight into the
receiver antenna. DSP software locks to the RF phase of this and I can then
measure the RF phase of any incoming signal relative to that, completely
independently of any drift or inaccuracy in anything else in the shack. So
long as the GPS is working and I can trust it, it's a true phase comparison
(i.e. a frequency comparison) made at the antenna input of the receiver.
73
Peter
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