W8JI:
> Maybe I'm wrong, but I get the impression a large part of our
> fraternity thinks noise is "electric" and signals are "magnetic". Well-
> intentioned articles then use that misunderstanding to explain the
> shield makes an antenna "magnetic", and that the shield somehow
> helps the antenna "filter-out" noise.
>
> Nothing is further from the truth.
Tom is right. Small vertical loops, infact, perfeclty couple with
vertically polarized antennas in the nearby.
It's a fact anyway, that medium size resonant small loops are far
superior if compared with a simple vertical in case of atmospherical
noises.
> Directivity is the only thing that eliminates noise.
Not exactly, also polarization or wave angle plays an important role
with local signals. Non directional antennas with a big response to
ground wave are sometimes a real pain in the neck with local noises.
> Delta's and other medium size terminated loops act like a pair of
> phased verticals (with a "feedline" between the vertical or sloping-
> vertical ends that also radiates a bit). Since they are more
> directional than the small loop you tried, they are quieter when
> properly oriented.
When the phisical spacing between two antennas is very small it's
generally not proper to talk about directivity. Phasing and mutual
coupling are quite critical and to obtain a pattern, a phase lag (and
energy) should be carefully adjusted all the times the frequency is
moved. On the other hand, with close spaced antennas it's much easier
to obtain a notch than a directional pattern, altough this is mostly
useless when one hasn't the opportunity to set the notch it in the
proper direction.
> An exception might occur if your noise was within perhaps within
> 50 feet of the antenna, and if you were very lucky.
>
> But the bottom line is small loops are mostly a waste of time,
It depends by the available alternatives.
> unless you have one groundwave noise source that you can
> position the loop to null-out. They are worth a try if you have room
> for nothing else and have local noise, but they are useless for noise
> that varies in direction.
Althoug critical and not very practical, I had decent results in
directivity when phasing two small resonant loops with a device that
allowed me to continuously vary phases and currents between antennas.
73,
Mauri I4JMY
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