Topband: Dual band shunt-feeding tower on 160/80

[Lennart M]

Interesting. I have tried verticals, slopers, inverted V's and other 80
meter antennas on or near my 160 meter tower with little success. 
The impedance of any such antenna seems to be severely altered by the nearby
tower. I suspect it depends on the electrical length of the tower. Mine is
close to an electrical half wave on 80 - 100 feet of Rohn 25 with a 7
element 6 meter yagi, approximately  30 foot boom sitting at 103 feet.

At one point in time the 160 meter shunt feed could be made to provide an
excellent match on 80 simply by changing the series capacitance. However,
after I cut down several nearby trees that no longer works.

73,
Paul N1BUG

Hi Paul and others,
I have a freestanding sturdy tower with yagis at the top. The entire setup
is selfresonated just below 1.8 MHz and being shuntfed from the top by a
number of large CU wires. Good bandwidth on 160. I also added a detuning
device to reduce reradiated noise when in receive mode on 160. This detuning
device also works fine as input for the entire structure via a parallell
tuned curcuit which can be switched in by vacuum relays. That give me a
little more than a half wave vertical for 80. Narrowbanded but good enough
for DX CW.
73
Len
SM7BIC