----- Original Message -----
From: jkearman@att.net (Jim Kearman)
Date: Monday, May 15, 2006 8:46 am
Subject: Re: Topband: QST Jun 06 RX Loop
>
> From: "Ford Peterson" <ford@cmgate.com>
>
> > I too was taken aback by the author's fantastic claims of 38dB
> nulls. Wow! Can
> > this be true?
>
> I used to live on a hilltop that was line of sight to a 1080-kHz
> BC station a few miles away. I had a large tiltable-rotatable
> unshielded tunable wire loop that could null it >30 dB. _BUT_ this
> was a groundwave signal of non-varying polarization. I suspect
> it's a small loop's ability to null by polarization that accounts
> for its better s/n performance, and not the 'shield.'
>
> 73,
>
> Jim, KR1S
> http://kr1s.kearman.com/
> _______________________________________________
That is true (by carefull construction and paying attention to symmetry,
deep nulls are achievable), but also in a case when you have local, within
fractions of wavelength distance from RX antenna, arcing noise source,
which in its proximity has predominantly electrical field,
then the electrostatic shield helps to attenuate THAT noise/signal
and improve local S/N situation.
THIS is the case when the shielded loop IS beneficial.
The distant signals and noise will look like "regular" EM waves
and will not be helped (much) by the electrostatic shield - loop.
I have tried it both ways, with and without shield and experienced the above
effect.
Yuri Blanarovich, K3BU
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