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VLF: Ground loop improvements and test carrier...

To: "[email protected]" <[email protected]>
Subject: VLF: Ground loop improvements and test carrier...
From: DK7FC <[email protected]>
Date: Wed, 03 Apr 2019 12:14:48 +0200
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Last weekend i improved my ground loop antenna by increasing its length from 900m to 1130m, i.e. +25 % of length, which should give about 2 dB more signal from the same antenna current. This is, when assuming that the shape of the virtual ground loop is rectangular.
Now when having two antenna segemnts it allows to do more research:
1. The resistance of each earth electrode can be calculated.
2. the shape of the virtual loop can be estimated: The resonance capacity (to series-resonate the R-L network at the feed point) can be compared for the 900m segment and the new 1130m segment. For a rectangular loop shape we would expect that the L rises with the square of the length.
The old loop was in an angle of 54 deg to my tree. This angle changed to
45 deg now.
I expected a theoretical gain of
G = 20 * (lg(1130/900) + lg(cos45/cos54)) = 3.58 dB.

A carrier transmission was done at 8270.1 Hz, using an antenna current of 2 A on both antennas.
900m Ant: T2019-03-31_13:58,+10m : E-field 26.8 dB, H-field: 33.7 dB
1130m Ant: T2019-03-31_14:12,+10m: E-field 31.2 dB, H-field: 37.1 dB

Looks like an improvement of 4.4 dB in the E field and 3.4 dB in the H field.
Attached is a spectrogram (11 mHz FFT bin width) showing the
improvement. The first dash is a tunng procedure, second is the 900m
ant, and the 3rd is the 1130m ant. Top is E field, bottom is H field.
I wonder how the level difference looks at other locations? Did someone
else track the data and can tell me the difference? :-)
73, Stefan

Attachment: 8270Hz_01.jpg
Description: JPEG image

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