Topband: Cage Vertical Worth It?

[W9UCW at aol.com]

Re: Cage  Vertical Worth It?
Hi Dan,
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 base 
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 top of 
the tower. 
 
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 stand-alone 
configuration first, I had a good chance to answer  the same question you asked. I 
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 the 
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 might 
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 were 
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, I 
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 
web.
 
73 and GL, Barry, W9UCW
 
 
 



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