Message-ID: <003701c0d083$29305360$c16674d5@w8k3f0>
From: "Dick Rollema" <d.w.rollema@freeler.nl>
To: rsgb_lf_group@blacksheep.org
References: <001c01c0cee7$3843ab60$ba62883e@g3aqc> <000601c0cf47$124ae620$a7ce28c3@ericadodd> <001f01c0cfca$3bb5fda0$f4eb7ad5@dave> <3AEB2DBE.194E5A9C@alg.demon.co.uk>
Subject: Re: LF: Re: Re: Re. Pre-amps
Date: Sun, 29 Apr 2001 10:04:32 +0200
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To All from PA0SE

Steve, GW4ALG wrote:

> 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.

Even when the coupling between vertical and loop is so weak that the SWR of
the vertical does not change when tuning the loop the coupling can still be
strong enough for signals from the vertical getting  into the loop.when
receiving.

73, Dick, PA0SE