> To answer your question a little more directly, I made a
few
> simulations. I considered the configuration you
mentioned, loading
> coils at the end of the 80M dipole, and 10 ft sections
hanging down, and
> assuming not winding an arbitrary coil, but one which
resonates the
> antenna on 160M: Also assuming negligible feedline loss
on both bands.
The last sentence is the rub.
Besides tuner loss issues feedline loss is significant on
160 for a short non-resonant antenna.
http://www.w8ji.com/short_dipoles_and_problems.htm has
loss data for an antenna 70% of the full size length and no
reactance compensation at the antenna. As we continue to
shorten the antenna (without reactance compensation at the
antenna) loss increases rapidly with small length
reductions.
> You will need about a 250uH coil - hard to build and
large.
> The resonance on 160M will be very sharp.
> The impedance on 80M will no longer be resonant, but
manageable with a
> tuner and 300 ohm balanced feedline. (Which you said you
were using)
> You will pick up only about 1 dB gain on 160M due to some
linearization
> of the current along the 130 ft wire.
> You will lose about 0.5 dB on 80M.
> Doesn't sound like it is worth the effort.
It may well be worth it when you consider feedline and tuner
losses. IMO the best solution is the suggestion to tie the
feeder wires together and feed the antenna like a "T"
against a good ground. A second choice might be to put
reactance compensation (the inductor) directly across the
feedpoint. The inductor would have minimal effect on higher
bands and require less inductance. That might be a solution
as long as it didn't make the feedpoint resistance too high
on 160.
73 Tom
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