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
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Stew Perry Topband Distance Challenge coming on December 29th.
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