You will find coupling with all tuned aerials placed close together whether
loops or wires, I put it as a sort of GDO effect in reverse. The tuned wire
is collecting a signal current and come of this is coupled into the loop
destroying its directivity. This should happen at 136 as well because the
near field region is even bigger, but may depend on the size of the signals
or noise that are being "collected". You can measure this effect with an
aerial bridge.
http://www.btinternet.com/~alan.melia/aecouple.htm
There was some recent EZNEC calculations published in QEX with investigated
resonant v non-resonant wires at different orientations to the driven wire.
(HF but the resulat are pertinent)
Cheers de Alan G3NYK
----- Original Message -----
From: Dave G3WCB <[email protected]>
To: <[email protected]>
Sent: 29 April 2007 10:47
Subject: LF: RE: 500 Loops (was PA2NL)
> Hi, Laurie, LF.
>
> I use a tuned loop for Rx on 136 kHz, and it is also affected by the TX
> "Tee" antenna. I use a relay to open circuit the earth return at the
bottom
> of the TX antenna ATU when the loop is in use. The problem isn't due to
the
> presence of the TX antenna wire itself, but the problems occur when the
wire
> is resonated by the TX ATU. The TX ATU earth has a 1 meg bleed resistor
left
> in circuit to leak away any static build up.
>
> 73, Dave G3WCB IO91RM
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of lawrence mayhead
> Sent: 29 April 2007 10:20
> To: rsgb
> Subject: LF: 500 PA2NL QRS
>
>
> PA2 beacon very strong here also, on the south coast.
>
> Interesting antenna effect:-
> I run a pair of large grounded loops situated close to the main TX
antenna
> (inv L )
> These have worked very well on 136 and are quite directional, providing
> useful
> improvement in SNR. On 500kHz however they are not directional, at least
> not
> in the right directions.
> I have spent several hours trying to find out what has gone wrong with
> them !
> By chance this morning I left the TX ant. grounded and was surprised to
> find that
> the loops are now directional. So it looks like there is much more
> coupling between the
> TX and RX ants on 500 than 136.
> Could this simply be capacitive ? perhaps I need smaller loops?
> Anyway if you are running a RX loop close to your TX antenna, beware.
> 73 Laurie.
>
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