Andy, UA3AB wrote:
"I need advise on how to make my tower to radiate on 160.
Tower #1 is 42m (140 feet) high with 3 el short Yagi (Force12 Mag340N)
atop it, Another antenna 5m(15feet) above it is 3 el 30m short Yagi
(Force12 EF330).
Another tower is 26m(90 feet) high with 6 el 20m and 6 el 15m Yagis atop
it. May be this is a better choice?"
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Either tower can easily be shunt fed using the single-capacitor ("gamma")
method.
My choice would be the shorter 26m tower because it will be close to
1/4-wave on 160m electrically with the top loading and therefore it will
have a wider 2:1 SWR bandwidth and less RF voltage across the gamma
capacitor.
On my shunt-fed towers, I use either #8 AWG stranded wire or old RG-58
coax for the shunt wire. They are both about the same diameter and their
flexibility makes them easy to adjust. Some shunt-fed tower users build
"cages" for the shunt feed wire, which slightly increases the 2:1 SWR
bandwidth, but not enough to make it worth the extra cost and effort,
IMO.
Rather than elevated radials, I advise that you use many on-ground
radials as the ground system.
Also, make sure the Yagi coax feedlines and the rotator cable come down
all the way to the ground before they leave the vicinity of the tower.
73, de Earl, K6SE
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