[Elecraft] Trap dipole fed with ladder line?

[Ignacy Misztal]

W9INN dipole is a dipole with multiple coils. When fed by ladder line,
it makes a lot of sense as opposed to a flattop fed also by a ladder
line.

Flattop with ladderline:
Good efficiency at bands >70% of half-wave frequency; too many lobes at
4 times half-wave frequency. Possibly hard matching for full-wave
frequencies (Impedance as high as 2000 hard to match).

W9INN with coax:
Good efficiency within narrow segments at 50% of half-wave size, poor
efficiency outside those segments. Smaller size than above for lowest
frequency. 

W9INN with ladderline:
Good efficiency with much broader segments at 50% of half-wave size,
Good pattern at high frequencies because coils in fact shorten the
antenna. 

Summarizing, a flattop for 80m fed by ladderline will work well on
80-20m, with a 4-10db loss on 160m, not too well on 17-10m, and may be
hard to tune on 40, 20 and 10m.  W9INN of the same size as 80m dipole
will work with minimal losses on 160-10m and will be easier to tune.

Ignacy, NO9E