Dave:
A 1/2 wave vertical can radiate at 160M with
resonable efficiency without an extensive
groundplane, though it is difficult to apply power
to it efficiently. The resistive impedance for
a half wave vertical will be in the neighborhood
of several thousand ohms. I have used my
1/4 wave 160M balloon vertical on 80M as
a 1/2 wave with 50 ohm coax feedline.
I matched it with a tuner - but the radiation
efficiency was low. The SWR at the feedpoint
is very high, so even at 80 or 160M there
is significant feedline loss through coax.
Power to a 1/2 vertical can be applied through
a parallel-tuned circuit at the feedpoint, resonant
at the same frequency as the antenna with suitable
components for the high voltages present. Another
solution is to use open wire feedline from the
antenna to the tuner. A 5/8 wave vertical may
be easier to match with a tuner and have lower
circuit voltages. A 1/4 wave vertical can be fed
directly with 50 ohm coax with an acceptable SWR.
73,
Jon N0JK
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