I'm looking for antenna designs that are omnidirectional (within, say, 3dB)
, horizontally polarized, reasonably small (say, <8-10 ft across), able to
be supported on a lightweight mast (field erectable), say 20 ft up, and not
too inefficent. Narrow band is ok. (as long as it's at least 5-8 kHz wide at
3.5 MHz, and able to be tuned remotely)
Comparing against the "Chu limit", something 10 feet in diameter will have a
BW of 75-80 kHz on 40, and about 6.5kHz on 80.
Therefore, we're not totally beyond the limits of plausibility. A real
antenna will probably have losses of 50%, which will increase the bandwidth.
One obvious choice would be a "compact loop" sized appropriately, but I
think that it might be a bit too heavy (supporting a 8 foot diameter ring of
copper or aluminum tubing 20 ft in the air)
Other ideas are something like a crossed pair of "shorty 40" style loaded
dipoles, but that's not actually omni, and if fed 90 out of phase actually
radiates CP straight up.
Something with the general properties of the Cobweb type folded dipole would
probably do, but not at being 15-20 feet on a side for 40m and twice that
for 80.
[ For what it's worth, I already have lots of data and design info for all
manner of verticals... I'm looking for Horizontally polarized]
Thanks,
Jim, W6RMK
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