[time-nuts] HF frequency counting receiver
jimlux at earthlink.net
Mon Jun 20 18:48:40 EDT 2016
On 6/20/16 1:44 PM, Graham / KE9H wrote:
> The ionospheric Doppler will spread the signal a few tenths of a Hz, YES.
> so getting millihertz is more random luck of the draw. NO,
> it is all about how good your averaging method/strategy is, over the period
> of the test measurement.
> A lot of the Doppler error can be averaged out.
> Some of it is an actual net vertical movement of the reflection point, as
> you said, worst at sunrise/sunset.
> Look at the scores/accuracy for some of the recent frequency measurement
You'd need to look at a lot of measurements to see whether the winner
just got lucky.
Looking at the 80m results and only taking the results that are within a
few Hz to remove outliers (N=93), the mean was 3,598,357.22 Hz with SD =
The actual frequency was 3,598,357.16, so the mean was about 0.1 Hz away
from the actual frequency.. I'd say the "winner" got there by chance.
In fact, if we do a standard test of significance, the 352.22 is not
different from 357.16 at the P<0.05 level (which is pretty crummy)..
Beyond that, ionospheric frequency shift might be something where
averaging doesn't help.
It depends on the propagation path uncertainty vs time. If it's long
term stable, then averaging will help. However, I'm not sure the
ionosphere is long term stable: the ionosphere literature seems to show
that phase variation at UHF frequencies (150 MHz) has a 1/f^3
characteristic. I'm sure that can be turned into an equivalent frequency
stability/phase noise, and in turn, into an AVAR type metric.
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