Hi TowerTalkians,
I had someone ask about my shuntfed 80/160 vertical and after replying and
explaining the whole thing to him I thought someone else might be interested so
am forwarding this. I"m definitely not recommending anyone build a vertical
this way.... just thought someone might find it interesting how easy it is to
get on the air.
Thanks Dan,
Problem solved... I blew the antenna :) Going to hang an inv L in the next
couple days.
I've got a 51' tower with a tribander on top plus a 40/80/160 trap dipole
hanging off an wooden stick about 1' away from the top of the tower. I know
having 80/160 verts underneath the dipole isn't ideal but wanted to experiment
with it. Experimenting, I attached a wire to the tower at about 12' up along
with about a 120' elevated radial. Checked it with an mfj antenna analyzer and
it was resonant very near to 1.8mhz! Obviously the 51' tower with tribander
couln't have that much electrical length but I assume that its interacting with
the dipole (even though the dipole is completely isolated from the tower) to
give it the extra length. So, I adjusted the radial length to get the thing
resonant exactly where I wanted it. Then I attached a coax at that point and
fed the coax to an ameriton remote coax switch.
For 80M I ran a wire up the tower, about 18" away, and attached it at the top
of the tower. Since the whole tower /tribander is resonant at 1.8mhz I knew
I'd have to really shorten it to get it to load up on 80M. I built a trombone
capacitor using 2 sizes copper tubing, mounted the capacitor at about 12' and
fed it against a 63' elevated radial. Between adjusting the capacitor and the
radial length I got a nice match with this vertical at 3.525. Attached coax
and ran it to the coax switch. Also ran the tribander into the coax switch and
I select the antenna from the shack. This, of course is the antenna that
couldn't handle the 800W (I'm not worried about the 160M vert handling high
power cuz my amp doesn't do 160M).
Now I'm going to replace the 80M with an inv L.
None of this is ideal of course.... especially the 1 elevated radio per band
situation... but fun to play with. The antennas seem about on a par with the
dipole. On 160 I'd say the vert beats the dipole, on 80M the dipole beats the
vert. But on both, there are times when the vert is better and times when the
dipole is better. More radials, I'm sure, would make a significant difference
and I'll do that soon. I'm going to add a couple for the 80M vert before the
weekend contest and I think, for dx, I'll see the 80M vert significantly better
the the dipole.
Good luck with your experiments.... 73,
Gary
Gary Slagel
Hot Springs, SD
N0SXX
http://marina.fortunecity.com/sanpedro/351
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