Wes Stewart wrote:

Hmmm. Interesting. I'm too busy to think much about this at the
moment but Devoldere has something in his book (p. 9-27 in my old
Third Edition) about decoupling a tower from ground using a "linear"
parallel-tuned trap.

Does this not work?

This sounds like the "resonance breaker" someone mentioned recently. It
resembles a gamma match. You put a wire parallel to the tower for a few
feet, then connect the top to the tower through a capacitor. The bottom
of the wire is connected to the (grounded) bottom of the tower. This
alters the effective height, and therefore the resonant frequency, of a
tower. It's a technique used in the broadcast industry to reduce
undesired coupling which distorts antenna patterns.

I don't think this method will do more or less than a trap. There's
nothing which will stop current or energy at some point, as long as
there's mutual coupling from the wire on one side to the wire on the other.

I recall an EMI control class I took long ago, where they told how a
brute force power line filter was installed to reduce radiation from
circuitry inside a device via the power line. Worked fine in the lab but
failed in production. The filter was physically placed where there was
room near the front of the unit, and they found that the production
folks had neatly bundled the filter input and output wires for some
distance, providing a good path around the filter. The same sort of
thing happens on a wire with a trap, although the coupling is of course
not as strong as between the bundled wires.

Roy Lewallen, W7EL