Your tower is probably just too tall for shunt feeding on 80, especially
if it has beams on it adding top loading. For comparison, my 70 foot
tower, with two tribanders and a 40 meter rotatable dipole, is about an
electrical 3/8 wave. (This from modeling.) I can shunt feed it on 80,
but the tap is near the top of the tower.
73,
Scott K9MA
On 4/26/2020 12:38, Ignacy Misztal wrote:
My 100ft 45G was installed with 3 sets of guy wires. The top 2 are
Phililstran and the bottom ones are EHS but with the top insulated from the
tower.
I tried shunt feeding the tower for 80 and 160. On 160m the results were
excellent. On 80, I could not find a good tap, with some weird impedances
changing every foot, so I put a 80m vertical 3 ft from the tower. The
performance on CW was dismal (10 db below a 100ft high dipole to EU) and on
SSB was excellent (few db over the dipole). I measured the resonance of
each guy wire with a clamp toroid and one loop, and all had resonances
close to 3.1 MHz with SWR 1.3:1. So clearly the guy wires were messing up
and were preventing the match with shunt feeding on 80m.
I put 2 clamp-on toroids on each guy wire as high as I could reach with a
ladder. Each guy wire is now resonant around 2.7 MHz. The vertical's
resonance moved from 3.53 to 3.62, but there is a second resonance on 3.4.
So my question is what to do especially that the vertical was just a test
for 4 sq. Keep the toroids knowing that they will eventually crack since
they are exposed to vibration? Move to Phillistran? Or is there another
(simple) option?
Ignacy, NO9E
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Scott K9MA
k9ma@sdellington.us
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