From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
Organization: Radio Society of Great Britain
To: rsgb_lf_group@blacksheep.org
Date: Mon, 21 Jun 1999 14:27:21 +0100
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Subject: LF: Antennas
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I have done very many antenna experiments over the past 2-3 
years to get a better signal at 73 and 136kHz from a small garden.

I have experimented with inverted-L Marconis. These have mainly 
sloped down from the top of the vertical section and I have on two 
occasions increased the height of the far end with improved results. 
It seems that at LF you cannot get away with drooping the far end 
of an inverted-L like you can at HF. This is presumably because 
the current distribution is approximately linear for a short Marconi 
and sinusoidal for something a quarter-wave or more.

One a similar topic, what influences the capacitance of a multi-wire 
top section? Is it simply wire diameter so a thick wire has more 
capacitance than a thin wire? What about multiple parallel wires - 
these are often suggested to be a metre or so apart - why? If the 
distance makes a difference, do I assume that the further apart 
they are the better the effect, and if so why is this?

I used to run three top wires about 300mm apart but replaced these 
with a single wire of the same diameter of each of the three (for 
other reasons) and it seemed to make little difference. Was I doing 
something wrong?

Also, if I run three top wires in parallel, should I join them at the far 
end? Or perhaps I could join them so they make a single zig-zag 
wire down the garden, back again and down again.

The antenna is getting better all the time, but I am sure there's 
more progress to be made. Does anyone have some practical 
experience to pass on?

 
Mike Dennison, G3XDV
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