Hello all,
Further to this discussion, I have done the ultimate test to demonstrate
that an active whip antenna with a 1 meter long whip behaves as a
capacitance at LF.
For the test I used the ground wave carrier of semi local NDB ONO at 399.5
kHz.
As it is the only station at that frequency the carrier level is very
stable at daytime.
The distance is 59 km, which excludes probably all skywave propagation.
The antenna was mounted vertical and the carrier of ONO produced a signal
level of -69.1 dBm as received with a PERSEUS SDR.
Next the antenna was mounted horizontal at the same height as the bottom
of the vertical mount.
This produce a signal level of -72.0 dBm.
I reasoned that the mean height of the 1 meter long antenna when mounted
vertical is 50 cm higher. So the antenna was then mounted horizontal 50 cm
higher from its previous position. This produced a signal level of -69.9
dBm, close to the value measured when mounted vertical.
The main point however, is that a horizontal polarized antenna should NOT
receive a vertical polarized ground wave signal at (almost) the same
strength.
So at LF, there is nothing gained in using a whip instead of a small piece
of copper clad PCB.
Comments are much appreciated!
Best regards,
Roelof Bakker, pa0rdt
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