> Many people who have horizontal loops have them low, which
is thought to be
> good for a big signal close-in -- some of us have
experienced having trouble
> working close-in stations with antennas that are high --
but a horizontal
> loop that's at least a half wavelength up should work fine
for DX, and I
> expect will be "quieter" (less QRN reception) than other
antennas, at least
> in some conditions. 73 - Rich, KE3Q
>
> > So, if the loop is big enough, and has the right angles,
it becomes a
> > useful
> > DX antenna ? The next question would have to be: How do
you work out the
> > required angles ?
I replied to Tim but probably should have CC'ed the
reflector.
There are many myths about loops. One myth is they are more
immune to QRN or noise, another is the peak gain from
multiple lobe patterns is useful or effective gain.
Whenever we see one thing touted as the answer for
everything, we better lookout.
Long loops can be forms of Echelon arrays if they have
correct spacing and stagger, like the receiving array at
http://www.w8ji.com/echelon-log_beverages.htm
We also have to remember gain always comes at the expense of
removing energy from some other angle or direction. The
small multiple sharp lobes from a loop do not produce useful
gain, because immediately next to each lobe is a deep null.
Unless you can rotate the loop, statistically some desired
signal is just as likely to fall in a null as on a lobe.
With narrow lobe antennas that cannot be rotated, we have to
plan the location of nulls or lobes or play roulette. The
signal might fall in a 20 dB hole just as likely as on a 6dB
peak.
Noise is a myth. HF noise rejection comes from the pattern
of an antenna, not the family of antenna. If an antenna
responds better in the direction, polarization, and angle of
a signal than at the accumulated noise from all other
directions, it will be quieter. That generally requires the
antenna have a very narrow clean lobe with a high ratio of
gain in the desired direction to average gain in all other
directions
http://www.w8ji.com/receiving.htm explains this.
I think the "low noise" myth is a carry over from quads.
Yagi's have sharp pointed elements protruding which produce
corona in inclement weather. The corona is at the high
impedance tips, and impedance at that point somewhat matches
the low-current high-voltage element discharge for maximum
noise transfer. A quad generally has blunt sides at the high
impedance point, and with well-insulated elements that are
compact it has less corona. As a matter of fact, the quad
was popularized from use at station HCJB where it was used
to reduce corona!
This noise difference in one special situation (hissing and
sizzling corona noise in inclement weather) gets pushed
along by myth and wive's tales to include general
applications where it is a total non-issue, like power line
noise or lightning storm QRN.
The primary advantage of loops, Rhombics, and such is wide
bandwidth and simple construction. The disadvantage is they
occupy a lot of real estate for the amount of useful gain.
73 Tom
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