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Cecil Moore · February 3rd 07, 12:32 PM posted to rec.radio.amateur.antenna

wrote:
Cecil Moore wrote:

wrote:
hmmmm, thats not what I recall being told but would it work?
one feed line?
A shorted 1/4WL 80m parallel stub will yield a
high impedance on 80m and a low impedance on 40m.
This is sometimes used with open-wire line to
achieve a match on both bands for a dipole that
is 1/2WL on 80m and 1WL on 40m. Also to open up
a 1WL 40m loop for use on 80m as a 1/2WL dipole.

I have seen this before, but somehow I would have to be able to connect and
unconnect the stub.

No you don't. The stub is a high impedance on 80m in
parallel with a low feedpoint impedance and therefore
has a negligible effect on 80m. It can be left in the
circuit.

The stub is a low impedance on 40m in parallel with
a high feedpoint impedance which lowers the SWR and
makes your transmitter happy. On 40m, the stub acts
as a low impedance load that eventually delivers most
of its stored energy to the high impedance antenna
(assuming the stub is made from low-loss transmission
line).
--
73, Cecil http://www.w5dxp.com