Re: Cage Vertical Worth It?
The vertical we used in Channahon Illinois in the 80's was built around a
120' tower sitting on busbar insulators with insulated guys. It had a 13 to 60
mHz conical monopole mounted on top making it 132' overall. Coax to the
monopole ran down inside the tower to the remotely controlled tuner at the
where it was connected to the shack when operating the higher frequencies.
I surrounded the tower with a 10' diameter cage of six #12 copper wires that
went down to an insulated ring around the base. The wires were held in
position by PVC pipes at three levels, starting from a couple feet from the
The wires acted as a ground plane for the conical monopole and as a
"fattening" element on the low bands. Having had the same tower in a
configuration first, I had a good chance to answer the same question you
experimented with feeding the tower and cage vs. feeding the cage and
grounding the tower base.
The latter arrangement made the antenna a caged folded quarter wave monopole
on 160 and significantly raised the feedpoint impedance. Of course, this
configuration could not be used on 80 meters, because as a half wave antenna
fields of the tower and the cage nearly canceled each other. The ground
system was made up of almost 12,000' of buried #12 copper wire. I guess it
be worth going back and digging it up nowadays.
We made several tests with stations out a few miles and were given "S" meter
reports of 3 to 6 db in favor of the folded monopole arrangement. That, of
course, is very unscientific and was relative to only ground wave signals and
lots of variables. We managed to get short term use of a Stoddard field
strength meter used in the broadcast industry. I don't remember what units
displayed on the Stoddard, but in tests out six miles the reading went from a
little over 7 to almost 21 when going to the folded monopole configuration. I
do remember that at the time, we calculated that the Stoddard readings jived
with the range of informal "S" meter readings.
As for bandwidth, the stand-alone tower with no cage installed gave us about
50 kHz below 1.5:1, as I remember. Adding the cage and feeding both it and
the tower base made it about 80 to 90 kHz below 1.5:1.
Feeding the antenna as a caged folded monopole added another 10 kHz making
it 100 kHz below 1.5:1.
BTW, the cage did offer some improvement on 80 in the form of reduced high
voltage problems in the tuner, as we were end feeding a half wave on that
band. I didn't notice the amount of bandwidth improvement on 80 but, frankly,
wasn't looking for it.
I hope that adds something to your quest, Dan. If you want pictures of that
installation, I'll be glad to e-mail them. Sorry, they're not posted on the
73 and GL, Barry, W9UCW
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