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 tests.
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 = 0.405 Hz.
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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