Nelson,
Although I haven't built one of these myself, there's a good write-up
by Al Merriman on this on Werner Funkenhauser's website:
http://home.inforamp.net/~funk/termloop.html
Basically, the idea is to use a remote controlled variable resistance,
such as a Vactrol to optimize antenna performance.
73's
George
----------
> From: Nelson Moyer <ku0a@blue.weeg.uiowa.edu>
> To: topband@contesting.com
> Subject: Topband: K9AY terminated loop
To: <topband@contesting.com>
> Date: Sunday, October 31, 1999 12:37 PM
>
>
> I finished my K9AY terminated loop just in time for the contest this
> weekend, and I spent some time checking its performance on 80 meters.
I run
> an FT707 which dosen't have 160, so that band will have to wait for a
new
> rig. From this early experience, it looks like the null off the back
is 3-5
> S units using a 560 ohm terminating resistor, but it's pretty tough
to get
> an accurate reading from the LED string on the FT707. I'm interested
in
> performance reports from other users, and I'm especially interested
in the
> terminating resistor values giving the best null for stateside
signals on
> 80 meters. I tried using an 80 meter ICE preamp, and that certainly
helped
> copy the weaker signals, but it also bumped up the QRN and QRM. The
> terminated loop isn't much quieter on recieve than my HF2V; certainly
> nowhere near as quiet as my small magnetic loop. The K9AY loop is
basically
> performing as a vertical with modest gain in the switched direction.
This
> impression is confirmed on 40 meters, where the antenna looses all
gain and
> behaves as a vertical, regardless of switch position. Is there
anybody out
> there willing to share their experience with a K9AY?
>
> Nelson
> KU0A
>
>
>
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