John,
"Height gain" at LF/MF is caused by quite a different mechanism from the
"height gain" at VHF.
VHF observations are irrelevant, I'm afraid.
Walter G3JKV.
----- Original Message -----
From: "John RABSON" <[email protected]>
To: <[email protected]>
Cc: <[email protected]>
Sent: Sunday, February 05, 2006 10:31 AM
Subject: Re: LF: {Spam?} Active_antennas
G8DSU has been doing some measurements on height gain at UHF and is also
interested in active antennas at LF for cave radio purposes. I will copy
this to him because I'm not sure whether he is currently reading this
list.
John G3PAI
*********** REPLY SEPARATOR ***********
On 05/02/2006 at 09:14 Walter Blanchard wrote:
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. Might do it myself sometime but
anyone else interested?
Walter G3JKV.
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