[TowerTalk] 56' Shunt fed? 40 and 80
K8RI on TowerTalk
K8RI-on-TowerTalk at tm.net
Wed Dec 27 22:10:23 EST 2006
It'd be easy to add more height ...Up to about 15' more which would be long
I'd guess about 64' would be close for a quarter way on 75 (middle of the
band) and very close to a half wave on 40.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
> your 56' tower is resonant at about 4.1 MHz - Give or take a bit. I'm
> modeling it with a 1' x 1' four legged tower.
> To shunt feed it on 3.5 MHz a #12 wire running 1' from the tower and
> at the 32' point looks good. It takes an 97 pF series capacitance to tune
> the Gamma inductance.
> To shunt feed it on 7 MHz a #12 wire running 1' from the tower and
> at the 26' point looks good. It takes 24 pF to tune.
> Relays can be used to switch the feedline from one GAMMA to the other.
> A single Gamma can be used at the 28' point with a motor driven variable
> capacitor. It looks like the minimum VSWR will be 2:1 on each band. A
> tuner at the
> shack can be used to touch it up.
> If you'd like I'll input more accurate dimensions for your tower. And
> depending on your ground we can add a bit of base resistance to make the
> more true-to-life. Then we can adjust the Gamma-to-tower spacing to find a
> compromise for both bands.
> Dave WX7G
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> TowerTalk at contesting.com
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