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Re: LF: LF Antennas

To: [email protected]
Subject: Re: LF: LF Antennas
From: "Mike Dennison" <[email protected]>
Date: Wed, 4 Apr 2001 10:22:21 +0100
In-reply-to: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
G3LDO wrote:
In an attempt to improve the reception on 136kHz by cutting down the Loran
racket I have, over a period of time, been experimenting with LF receiving
loops. I now have one that works really well. It was used for the first time
in a 'reverse' crossband (136kHz/3.5MHz) QSO with VE1ZZ on 21st Feb.
Details of the construction and pictures are on the site shown below - click
'An efficient LF receiving loop'.

Recently, Mike, G3XDV, elevated the loading coil on his 136kHz Marconi. This
reduced the antenna current but apparently improved the efficiency. I am
researching material for a mobile handbook and was looking for a graphic way
of illustrating why elevating the loading coil improves efficiency. What I
have written is shown and illustrated on the site (I am sure that it must
have been all done before!). Click 'Discussion'. Any comments direct or via
the reflector welcome.
Peter,

Thanks for providing these useful pages. The following may also be helpful:

Although you deal with the matter of increasing the length of the higher current part of the antenna, the other way of looking at it is that the effective height has been increased. This then ties in with the ERP calculation.
Another potential gain is caused by the considerably reduced voltage present
on the part below the coil. Losses due to proximity of nearby walls, trees etc
are consequently reduced.
It is also worth saying this is effective when the part beyond the coil is quite
small (as in your straight vertical diagrams). For an antenna with substantial
top loading, the gains and losses (caused by the much large inductance
needed) can cancel each other out.

Lastly, it would be helpful if you had a What's New page - or perhaps a box at
the top of the main page - as it is quite difficult to locate new material with the
present structure.
73


Mike, G3XDV (IO91VT)
http://www.lf.thersgb.net



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