Hi William, All,

As is common with comparisons, the problems arise due to the shifting
sand these arguments are built upon.

On Wed, 14 Jul 2004 12:09:17 -0400, William Mutch
wrote:

But, my point was that no improvement in S/N was reported in the original
post.

True; I didn't report it but it is there. Typically at most
frequencies the desired signal is reduced 1 to 2 S-units with respect to
the whip antenna (strong ones) or my high long wire weaker signal...156
feet AWG 16 up 45 feet fed off center w/ a 4:1 balun) but the noise
level is reduced by anywhere from 3 to 6 S-units...a very! worthwhile
tradeoff.

Presumably, the comparison is loop vs. these others. It is not
explicit and that is one of the problems of reporting and subsequent
interpretation - hence the observation in the double quote above.

However, the "issue" is more has anything really changed? A loop
(dipole) compared to two verticals. Arguably the so-called off center
fed long wire is presumed to be a dipole, however (again poor
reporting) nothing says of this antenna being choked. Lacking that
choke offers every inducement of Common Modality (the antenna is,
after all, fully and admittedly unbalanced by its very description).
Common Modality is ever bit a noise hazard as any vertical (is
supposed to be - another nightmarish fantasy under the bed).

Hence, any perceived boon of noise reduction comes as a consequence of
the loop's faithfully performing as a - dipole! Wonders never cease.

Exact quantitative measurements are not possible on the
Sat800 RCVR because you can't turn off the AGC.

I don't know how this got started as a unnecessary evil - AGC is what
drives the S-Meter. AGC is only an issue if you want to derive signal
strength via modulation levels - which nobody here does anyway.

My understanding of why
the shielded loop performs this way is that near field noise is
cancelled while far field signal is only attenuated by some factor
relating to capture area. In my temporary rooftop mount I was unable to
easily check out the effect of broadside null.

Tom has posted in this thread very simple metrics to obtain just what
constitutes near field. The incantation of near/far fields belies
simpler explanations. If there is any issue of noise that relates to
its nearness, it follows that you are the source. You being the
source means that you also have the capacity to correct (and building
a magic antenna is possibly the most superstitious response to that
problem). The loop simply has less coupling (and less signal - that
means there is a constant of proportionality in S/N) than a full sized
dipole sitting over this noisy domicile. I have a random wire antenna
that passes within 2 feet of an 80W Fluorescent fixture with a humming
ballast. I barely pull in S-1 worth of noise and a loop would stand
to do worse at that same distance. If I find that little noise
troublesome, I turn off the noise.

The fact that the shielded loop performs as a dipole is proof of its
efficient construction (many fail to achieve even this). There is
very little more that can be said about its qualities short of its
loss of sensitivity.

73's
Richard Clark, KB7QHC