Message-ID: <3AF58211.1312A631@alg.demon.co.uk>
Date: Sun, 06 May 2001 17:55:45 +0100
From: "Steve Rawlings" <steve@alg.demon.co.uk>
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Re: Coupling between two antennas
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from GW4ALG>

I'm very grateful to Bob ZL2CA for his important observations and
comments.  

Firstly, a couple of points of clarification:
1) My loop is orientated in the vertical plane.  It is a
delta-loop, having a 65 m perimeter, fed at the top with balanced
feeder.  The line of the loop runs east-west, and therefore has
deep nulls to the north and south - very handy for attenuating
the noise sidebands from the Loran TX, located to the south of me
(in France).  Further details can be found at:
http://www.alg.demon.co.uk/radio/136/loop.htm
2) The vertical antenna is located at one end of the loop.

> The absolute gain of your short vertical will be higher than your 
> loop, so whatever figure of mutual coupling is found to apply, on
> receive the loop will be affected more by the tuning situation of the
> vertical than the other way round.  With smaller frame loops for
> receiving the impact of the vertical for reception on the loop is even
> more pronounced (due to the much higher absolute gain of the vertical).
I had not appreciated this important point before now.  I guess
it's one of those 'key facts' that every LFer needs to learn.  

> I find that on receive, unless the LF vertical transmitting antenna is
> detuned, it receives local QRM from a fairly wide area and re-radiates
> it to any LF receiving antenna on my property.
Again, thanks for the tip, Bob.  I'll try and detect that effect
with my own set-up.

Regards to all,
Steve GW4ALG