[TowerTalk] 160 M antennas: Shunt feed, reverse feed or just a vertical...
rxdesign at ssvecnet.com
Wed Dec 30 19:40:35 EST 2015
Ok.... I’ve been reading through pasts posts and I’ve digested both UN’s book as well as the ARRL AB regarding each of these:
-Shunt feed tower
-reverse feed tower
-plain jane vertical
... I had an inverted L in Arizona - ~100’ vertical section spaced about 35’ from my 143’ tower with stacked antennas on it ... I had 32 radials all about 100’ long and it performed extremely well I thought (my first time on 160: worked DXCC in 89 days from first having put it up) ...
I’m now in South Carolina and have a tower that is going to be about 100’ tall at the top of the mast with a 31’ boom 6 meter beam at that point and various other beams below it with a 7 element 10 at the ‘bottom’ at 40’ (one of two) ... It will of course have insulated guys.
I had planned on duplicating the inverted L – taking it off the 122’ level of the big tower allowing about the same 100’ vertical section spaced about 100’ from either tower with about 40 or so radials just below ground level. Lets call that Plan A.
Plans B and C would both use the above mentioned ~100’ tall tower:
Plan B could be a gamma matched use of the 100’ tower. I figure its around 110 degrees or so on 160. But the gamma attachment point has to be no higher than the first guy at about 38’. That might be a problem – I might be forced to go to an Omega match... and then the same ~40 radials underground...
Plan C is having say 4 elevated radials at about 18’ – 20’ ... connecting the center conductor to the tower at that point and the shield to the 4 radials and trying to ‘tune’ this arrangement. And then 40 radials (not connected to the tower) just underground at its base.
So.... Plan A, the L, I had great bandwidth out of this in AZ where it was 1.3:1 at 1800, 1.1:1 at about 1827 and was 2:1 at about 1920Khz.
Plan B and C are unknowns although years ago I tried to shunt feed a tower and found that it had very narrow bandwidth (and super high voltages across the gamma capacitor). Is this true or would one expect wider bandwidth?
Last: I’ve seen people comment about all the other cables if I do plan B/C ... one said “they didn’t matter” ... others say the more common “you have to isolate them”. So assuming you do have to isolate them does that mean :
for the gamma match version with the coax near the bottom that all cables need to have their shield connected to the tower at the base? I had planned on hardline to the yagis so doing coaxial baluns (coiled coax) isn’t practical...
The simplest one seems to be the L ... just drop a wire down and connect it up... am I missing something else?
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