Dave Platt wrote:
In article t3ali.3392$Y_3.570@trnddc04, Woody wrote:


Well.. a million thanks for that. Quite a cool history lesson as well. So
now I'm looking for an SEA tuner... LOL...

Listen, that all makes perfect sense but just to clarify, a.) now I know why
that triton did so poorly when tested. We calc'd 1/2 wavelength for the
longwire, and b.) Again, for continuity and clarity of this thread for
future surfers...... what then, considering our discussed auto-tuners, would
be the optimal length for a longwire that would be used for amateur/MARS,
3-30MHz?
Pick 1/2wavelength on say 2.8Mhz and just cut it? Or calc 1/2wavelength on
the lowest and add 5% or some arbitrary odd number??
Which plan will offer the least chance of dropping a 1/2wl further up the
band on a desired frequency?


I think you'll need to run a a simple calculation, based on the
frequencies you actually want to use.

What you'll want, is a wire whose length is not particularly close to
any multiple of 1/2 wavelength, on any frequency you want to use. A
wire which would match easily on 80 meters (e.g. 1/4 wavelength long)
would be a bad choice if you want to work on 40 meters as well, as
it'd be 1/2 wavelength long.

A simple program or spreadsheet ought to be able to do the necessary
calculations... try every wire length from 66 feet to 132 feet and see
if you can find a length which is a comfortable percentage away from
an even multiple of 1/2 wavelength on each frequency. Or,
alternatively, iterate through each frequency, calculate the
1/2-wavelength multiples, and "blacklist" every possible length which
is too close to these multiples.

For what it's worth, SGC sells a longwire antenna 60' in length, which
they say works well on both lower and higher HF bands. It might or
might not be a good choice for MARS frequencies.


The other strategy is to use two wires of appropriately different
lengths connected together at the feedpoint. (the SGC whips do this, for
instance).. Space the wires some distance apart (a few inches would
do).. What this does is put multiple bumps in the impedance curve and
eliminates the pathological cases where you have very high Z when the
(one) wire is a half wavelength or multiple thereof. At those
frequencies where one wire *is* a half wavelength, and presents a high
Z, the other one is likely NOT a multiple of a half wavelength, and so,
will present a reasonable impedance. Sure, they interact (as folks
making multiband dipoles find when trying to cut and trim), but all that
really does is shift the resonances around.

An interesting question would be what is the optimum ratio of lengths..
probably something like 1:1.618 or 1:2.7183