I am trying to quantify the efficiency of trapped h.f. antennas
references tell me that -traps are lossy and trapped antennas are
inefficient.I cant find a reference to the typical efficiency, is it
20% ,40% or is it 90%?
A former commercial amateur antenna designer told me to use
1/10 dB per trap as a "rule of thumb" for well-designed traps.
Using this number, an A-3 tribander has 12 traps in the circuit
on 20 meters, and would be 1.2 dB down. The losses are also
compounded by the parasitic elements. For example, 4/10 dB
loss in a reflector results in more than 4/10 dB lost gain (but I'm
not sure how much).
Maybe Steve at Cushcraft or Roger at Hy-Gain can shed some
more light on the matter. A reliable number for trap resistance
would be very useful for modeling.
Some older designs will have greater loss. My one-sample
personal experience is the replacement of an old Moseley
Classic 33 with a Hy-Gain Explorer 14 -- the improvement
was astonishing. The older Moseley had directivity, which
indicated that it was working OK, but between the traps,
tuning and feed design, it was barely better than a dipole.
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