Re: LF: RE: Todmorden receiver

[Paul Nicholson <vlf0403@abelian.org>]

Varying the E/H mix on recent carriers and EbNaut signals
fails to improve S/N when I move away from the calibrated mix.
That's a good sign but it's not quite right yet.

Measured E/H is tending to come out a little on the high side
of 376 ohms, where it should really be equal to or lower than
the free-space value.   Lower with more local signals which
would have higher elevation of incident signal.

Today I measured the loop area more carefully.  The ground
beneath is uneven so I had to integrate - just W*H is no
longer accurate enough.    The nice thing about loops is that
they are easy to calibrate accurately, compared with E-field
probes which need careful modeling of charge distribution to
determine the effective height.

The E-field model isn't quite right at the moment since I
repositioned the clamps.  I think the effective height is
higher now than modeled.  Perhaps enough to fix the error?

If the calibration can be refined sufficiently well, it ought
to be possible to adjust the antenna synthesis not just for
azimuth, but for elevation and polarisation too, to achieve
a further small increase in S/N.

fbins spectrogram is currently running with the old calibration
and therefore won't have a good front/back ratio or optimum
sensitivity.  When I've pinned down the calibration a bit
tighter, I can recalculate the spectrogram data, backdating
to midday 20th when the new H rx was activated.

> better keep some of the sausages ;-)

Nobody had a camera the other day to capture the bizarre sight
of someone running along a muddy farm track carrying a car
battery and a spectrum analyser with an angry dog snapping at
his wellies.  I had no spare hand to throw sausages.

--
Paul Nicholson
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