Billy, without getting too far into the technical, your answer to
Why does not the 20m dipole work twice as well on 10m, (hope I am
summarizing your thought correctly) is that Antenna effective area differs
from geometric area by a k factor.
However, in dealing with wire antennas such as horizontal loops over equal
ground, & equal other parameters, you will have greater and worthwhile gain
as you go higher in frequency, ie an 80m loop used on its harmonics. There
are indeed pattern differences in the classic modeling. In actuality of
operation, ionospherics are so non uniform that pattern lobes do not limit
usability of a given azimuth direction from the loop on the harmonic bands.
This is a topic of ongoing experiments, from a uniform site used each year.
It has been a rewarding finding of going to the large horizontal loop,
(several wavelengths on the frequency in use). However, as in all antennas
there is no free lunch, and you must live with mechanical demands of wire
tension limits, sag, static build up and dissipation, etc. In a free space
case, lobing and nulls are shown, but less a problem in wide area use such
as Field Day.
Loop Symmetry is important we find in the achievement of best operations as
a near omnidirectional radiator. Other geometries can be effective in the
directions of longest sides, but you give up some gain in other directions.
One must steer the lobes as needed by careful siting, and have the antenna
free of outside influence, just as in any antenna.
-Stuart
K5KVH
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