Topband: KLM antennas on shunt fed towers

[Tom W8JI]

>A little different version of this question - is there any general guidance 
>about what to do with pickup on other antennas when transmitting?  Shunt 
>the pickup to a dummy load?  short?  open? something else?

Never a dummy load, but sometimes open, sometimes short, or sometimes 
reactance. It really 100% depends on feedline lengths, grounding, and how 
the antennas and feedlines we want to make "go away" or have trouble with 
behave out-of-band.

As an example, my ~220 foot tall insulated base tower fed through an L 
network required a modest length of open-circuit coax to detune it, or it 
totally destroyed my 160 meter 4-square. I can change the coax length and 
make it require a short, or I can add a lumped reactance instead of a 
certain feedline length.

We have to look at the **system's** behavior on the band where it is being 
externally excited,  otherwise we are just throwing things at a wall hoping 
a wild guess somehow makes things better.

> I'm adding a vertically polarized pair of phased 80m delta loops (ON4UN 
> design) on one tower with a 40m Moxon and a 80m rotary dipole above their 
> apex.

How the delta loops, baluns, and feedlines behave in common mode on 160 
meters, along with how the Moxon and 80M dipole, baluns, and feedlines 
(including grounding) behave on 160 is key to what happens and what you need 
to do.

Errors or neglect like this are what creates all the "terrible" and "great" 
abnormal changes reported on multiple antenna or structure, or spread-out 
convoluted antenna system installations.

I tell this story often, but one Ham in Toledo had dozens of wires and a 
couple towers, including feedlines and guylines, in a pretty large back 
yard. He was always way down in signal level from a fellow with a simple 
clean well-planned antenna on a postage stamp lot. He'd accuse the other guy 
of all sorts of illegal power, when the problem was really his. He had so 
much unplanned stuff in his yard he was lucky anything worked at all. The 
moral of the story is it's not possible to get a magical increase, but it's 
easy and common to get or remove a magical decrease.

73 Tom