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Re: LF: Re: Re: Re. Pre-amps

To: [email protected]
Subject: Re: LF: Re: Re: Re. Pre-amps
From: "Dick Rollema" <[email protected]>
Date: Sun, 29 Apr 2001 10:04:32 +0200
References: <[email protected]> <[email protected]> <[email protected]> <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
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




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