Hi Jim...My first shunt-fed tower was similar to yours (in Connecticut,
1978). It was 70 feet of Rohn 25 with a 204BA on top and a 4-el 15m Wilson
yagi a few feet above that. As I recall the 160m shunt was up about 40 feet,
out about 16-18 inches, maybe more.
I know the 80m shunt was a lot shorter; only about 15 or 20 feet up perhaps,
and out maybe 12 or 18 inches.
Had about sixty 1/4 wave (for 160m) radials (copper-clad steel electric
fence wire, laid on the ground in woods). With the top loading, it probably
was close to being an electrical 1/4 wave on 160. It was a fine radiator.
Brought my country total up to about 83 on Top, back when that was a big
number, before moving to Delaware in '81.
On 80m, this tower works out to be about 1/2 wave electrical length. So it
must have had great low-angle radiation. It was a super antenna for working
the long haul -- VK, ZL, and JA. But for working Europe, it was terrible.
I'd call and call and call -- and they just couldn't hear me. Finally went
back to using a dipole at 50 feet in the trees to finish up 80m DXCC.
73/Jon AA1K
At 09:03 AM 11/26/96 +0000, you wrote:
>Hello Topbanders,
>
>I have a 65 ft tower with a TH7 and 40-2CD on top and 16 radials from
>1/8 to 1/4 wavelength long. I have shunt fed it for 160m with a
>jumper across the 18 inch spaced shunt at abt 50 ft. It seems to
> work pretty good. The SWR is almost flat across the entire 160m band.
> Is that typical?
>
>I also tried to add an 80 meter shunt on the opposite side of the
>tower. I havn't been able to find an optimum jumper point on the
>shunt. The lowest SWR has been 2:1 and the bandwith is quite narrow
>(which is OK). The performance has been poor. I probably just need
> more time to refine it. My question regards interaction between the
>two shunts. It appears that the 160m performance has decreased since
> I added the 80 m shunt. Could this be true or is it just my biased
> judgement or band conditions?
>
>Have any of you had success with a combo 160/80 m shunt fed tower?
>Any guess where the 80 m jumper would be with 18 inch spacing?
>
>Thanks for reading my questions and for your response if you can
>help.
>
>73,
>
>Jim Hood, K5TT
>President, Oklahoma DX Association
>wv5s@icon.net
>Past operations: KC6SS, V63SH, /XE, /WH6, /NH7, /KP2
>Previous calls: WV5S, W0PUD, W7KDH, K5TWD
>USA-CA # 432
>
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>
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