[TowerTalk] guy wire interaction with 80m

[K9MA]

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 at sdellington.us