[TowerTalk] Stubs and Reactances in parallel

[Steve London]

The antennas are fed separately. The stub on the 80 meter dipole does kill the 
interaction to the 40 meter beam. However, the Z of the stub is around 1000 ohms 
80 meters, so it affects the 80 meter dipole. Read my earlier writeup carefully 
for details.

73,
Steve, N2IC

On 6/24/2020 11:20 AM, Steve London wrote:

     Is there another solution I am overlooking ?


Hi Steve,

Yes. Feed the two antennas separately. Use a stub in the 80M feedline as 
detailed here to kill the harmonic of 80 on 40.

http://k9yc.com/LocatingStubs.pdf and
http://k9yc.com/StubPlacement.pdf

The same stub, properly placed, will apply a short at the feedpoint of the 80M 
antenna, which should kill the interaction. I learned this a few years ago doing 
an NEC model of our contesting trailer's antenna system k9yc.com/7QP.pdf I work 
with N0AX on the Handbook and Antenna Book, and when I told him what I'd learned 
he nodded his head yes, he'd known about that for years. The ancients keep 
stealing our inventions. :)


Also, remember that VF varies enough with frequency that stubs must be measured 
and tweaked to length at the frequency where you want them to be a short. The 
variation is enough to move their resonance to a different part of the band.


73, Jim K9YC