David,
I hate to break the news to you but theory and loads of experimentation have
shown that the horizontal portion of a wave this long is short-circuited by
the ground surrounding the transmitting antenna. Therefore a horizontal LF
dipole is very ineffective at any practical height above ground. This why
verticals and loop antennas (mounted in the vertical plane) are used
exclusively at these frequencies. You may find, however, that your long
dipole turns the conductive portions of the soil into some kind 'ground
antenna' having a vertical component... so I wish you well. And keep us
posted!
Bill A
-----Original Message-----
From: captbrian [mailto:[email protected]]
Sent: Saturday, August 02, 2003 8:18 AM
To: [email protected]
Subject: LF: Re: 500m drums of coax dipole
Is there the slightest evidence that 136 propagates (propogates?) by
scatter or reflection.? I assume most of a 2" high dipole radiation goes
straight up to Mars.
Bryan
-----Original Message-----
From: [email protected] <[email protected]>
To: [email protected] <[email protected]>
Date: 02 August 2003 11:47
Subject: LF: 500m drums of coax?
>Are you making a coax dipole for 136?
>
>73
>John Rabson G3PAI
I've always wondered about dipoles / loops at 136k?
A 'dipole' just lying on rocky ground where the water table is many metres
below the surface could be quite effective. The angle of radiation would be
poor
but the efficiency may not be as bad as first suppossed. One advantage of a
big antenna on the ground is that it can't fall down and, for the local
planning committe, it's less than 9 feet high.
Some time ago I tried to simulate this by making a dipole for 21MHz and had
a
number of QSOs through it while gradually lowering it's height and
retrimming
as I went. I managed to work Romania were I sent "Ant dipole 5cm agl". I
have no idea what the Romanian though of this madness and he didn't stay
around
long to find out.
Incidentally, at about 2 inches off the ground the antenna was resonant at
about 20% less than it's normal 'free space length'. Never did find a big
field
to try it on 136k.
73
David G0MRF
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