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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|