[TowerTalk] 80M Ideas

[Jim Brown]

On 12/27/2012 7:50 AM, Jack White wrote:
> I have a painted 3 section 60ft Versatower (suspect v. poor electrical connection between sections) with an Optibeam OB1-4030, Optibeam OB9-5 and 5L 6M Yagi all mounted on a 15ft stub mast

Several thoughts.

1) You may think that the connections are crummy, but a smart EE friend 
who works with towers a lot has observed that with all the weight that's 
on it, and the considerable cross sectional area in contact at the tower 
junctions, most towers are likely to have connections good enough to 
load.  I'd say it's worth a try.

2) That tower WILL interact with any vertical antenna that you put 
anywhere near it, and "near it" is within more than 100 ft on 80M. My 
120 ft tower interacts enough with  my 160M vertical that's about 210 ft 
from it to give me 3dB of useful directivity going south, and  a 3 dB 
null going north. If I model my 45 ft tower with a couple of monoband 
Yagis on a 16 ft mast, it puts a 2dB bump in the 160M vertical.

3) If I were you, I would study the ARRL Handbook, the ON4UN book, and 
the ARRL Antenna Book on the topic of loading towers, and I would also 
study N6LF's excellent website, and I would use what I learned to either 
load that tower or use it as a passive reflector for another vertical.  
Rudy has a great paper on tower interaction that will surprise you.  It 
sure surprised me, and NEC confirmed what he was observing.

4) Consider the possibility of hanging a sloping wire off the tower, fed 
from the botom of the wire, insulated from the tower. Depending on the 
tower height, it may work as a passive reflector, and as you describe 
it, I suspect it will.  I'm doing exactly that on 160M, and it works 
well.  You will need radials on both the tower and the sloping wire.

73, Jim K9YC