Topband: 160 shunt fed tower update

[Steve London]

When we last left this adventure, I was shunt feeding my 110' tower on 
160, which supports a multitude of yagis and wires. Unfortunately, I was 
coupling so much energy into the 80 meter wire array that the 80 meter 
baluns were heating up. There were a number of interesting and useful 
suggestions on this reflector.

As an experiment, I disconnected all of the feedlines going from the 80 
meter switching/tuning box at the top of the tower to the individual 
elements of the 80 meter antennas. The 80 meter wires were still in 
place, just not connected to the tuning/switching box. That solved the 
balun heating problem, and greatly changed the shunt feed point and 
spacing needed for 50 + jX at the tower base feedpoint. I left it that 
way for several weeks, while I evaluated how well the shunt fed tower 
actually worked. Based on comments from topband readers and performance 
in the Stew Perry, I was satisfied it was working effectively.

The next step was to build an insulated bracket to support the 80 meter 
switching/tuning box to keep all of the 80 meter coax lines electrically 
insulated from the tower. No torroids. No grounding of the 80 meter 
feedline to the tower. I was hoping this would keep the 80 meter array 
RF isolated from the shunt fed tower. No such luck. The shunt feed 
needed significant adjustment. There is significant coupling, despite 
having no DC connection. The good condx to EU most evenings this past 
week have been very frustrating as I struggled to work "easy" stations 
that were no problem to work in the past with the old sloping dipole. I 
have to conclude that the coupling is having a detrimental effect.

Yes, I could experiment with torroids, etc., but my conclusion after 
reading comments here is that nothing is guaranteed to fix the 80 meter 
coupling problem, short of removing all the 80 meter wires.

Back to the drawing board. Maybe a dedicated 160 tower is in the works.

Hope to work some of you in the NAQP. Listen for the weak signal from 
New Mexico !

73,
Steve, N2IC