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The theory behind the "height gain" observed
using small LF active antennas at different heights has to do with compression
of the near-earth LF potential gradient caused by the grounded "mast" holding
the antenna.
The essential bit is that there is a grounded
connection between the antenna and receiver, which may be just the outer of the
co-ax cable.
It would be an interesting experiment to repeat
the "height gain" experiment without any connection to ground.
This could be done by building an active
antenna with a little transmitter to re-radiate the received LF signal (on 2.4
GHz?) and poking it up using a fibreglass mast.
If the theory is right then there wouldn't be any
height gain.
Sticking to the KISS principle, how about hauling say, a battery powered
SPM-3 selective level meter up a fibreglass mast and observing the signal
strength at various heights through a pair of binoculars? :-)
Tracey
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