On 1/20/20 1:13 PM, Bob kb8tq wrote:
Hi
I think you will find that some fairly generic oscillators will hit the “more or
less 1x10^-10” sort of spec needed for HF com work. A good OCXO will get
you into the 1x10^-12 range. The limit generally is the “floor” imposed by
propagation variance at HF.
Bob
And the source's phase noise. There are relatively few "spectrally pure"
transmitters in the HF band that are sufficiently clean that you can
measure the ionospheric effects. WWV/H, ARRL FMTs, ionosondes (maybe),
and a few other things.
For what it's worth, the decorrelation time for ionosphere is about 3
seconds. That is, the state of the ionosphere on any given path is
almost entirely uncorrelated to the state 3 seconds earlier. So AVAR at
100 seconds isn't worth a whole lot, unless you're measuring the ionosphere.
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