Message-ID: <3AEB2DBE.194E5A9C@alg.demon.co.uk>
Date: Sat, 28 Apr 2001 21:53:18 +0100
From: "Steve Rawlings" <steve@alg.demon.co.uk>
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Re: Re: Re. Pre-amps
References: <001c01c0cee7$3843ab60$ba62883e@g3aqc> <000601c0cf47$124ae620$a7ce28c3@ericadodd> <001f01c0cfca$3bb5fda0$f4eb7ad5@dave>
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Dave G3YMC wrote:

> I am following this thread with interest because as you know I use my
> transmitting loop as an excellent receive antenna.  I do not (yet) have
> a vertical resonant antenna for the band - I would be interested in
> Steve GW4ALG has any problems in loop detuning from his main antenna, 
> as his loop is of similar dimensions to mine.
Although I have never noticed any detuning of my vertical antenna
when adjusting the tuning of my loop antenna, the message from
Dave prompted me to check this out right away.

I have a single-turn delta loop of 65 m perimeter, and also find
it excellent for receive.  It is fed at the top using balanced
feeder and is tuned & matched to 50 ohms with a balanced tuning
unit.  No pre-amp is used.  Details can be found at:
http://www.alg.demon.co.uk/radio/136/loop.htm

My 12 m experimental vertical antenna is very close to one end of
the loop.  For details see:
http://www.alg.demon.co.uk/radio/136/experi_vert.htm  

This evening, when monitoring the TX SWR into the resonant
vertical (very close to 1:1), I found no change in SWR when:
- tuning the loop antenna either side of resonance (with the
coax-side of the tuner terminated in 50 ohms);
- disconnecting the shack end of the balanced feeder from the
tuner;
- applying a short circuit to the shack end of the balanced
feeder; or,
- grounding the shorted balanced feeder.

As you can imagine, the tuning of my short vertical is very
sharp.  I can even see the SWR change when the wind blows.  So
I'm very surprised that there appears to be so significant
interaction between the two antennas.

Regards to all,
Steve GW4ALG