[time-nuts] Odd-order multiplication of CMOS-output OCXO

[jimlux]

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.