For 160/80 some features under discussion and used, both at home and for
V7, were a 55' vertical + drooping T (2x or 3x wires at ~ 45 degrees but
reachable from the ground for initial tuning) + two/few experimentally
tuned elevated radials for each band. The raw antenna is long on 80 and
matched by a series cap (air with enough gap for power). It is short on
160 and can be matched by a hairpin coil across the input. Of course,
you must somehow switch between the cap and the coil to change bands --
not completely trivial. In my case, this done by hand at the base amid
the dark/rain/snakes. Especially on 80 this antenna is significantly
off-center-fed and required substantial extra coax coiled up as a choke.
The story is written up on my website. This method probably has limits
on 80 if using just a field of 160 m ground radials, although adding a
couple of elevated tuned 80m radials might do the trick - or so says
standard EZNEC. EZNEC also hints that you might also be able to have a
mix of 160 m and 80 m radials to get a similar effect but the limits of
EZNEC when radial ground effects may be important are well known.
This antenna had acceptable (second-tier in pile ups) performance on
160m using 700 watts and was quite good on 80. The V7 version with 2
drooping T wires and 2 elevated radials for each band was just okay on
160 but good on 80, probably limited by trees proximity and restricted
geometry, although some might claim enhanced by being on a beach with
adjacent ocean.
Bill N6MW
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