Topband: 160M ant interaction on 20M

[Ford Peterson]

I installed my new 3 el SteppIR antenna a couple of weeks ago.  Some pattern
distortion was noted on the bottom of 20 meters.  No F/B.  The antenna works
great, except for the bottom of 20M.

I built a small shielded loop on the end of 3' of PVC last night.  Hooked it
to a relative signal strength meter.  Set the rig to 100W and went sniffing.
It was like a mine sweeper.  Get within a couple of feet of a radiating
object and the meter would jump.  It turns out that it's the 160M drop wire.

I shorted it out with an aligator clip and the problem with 20M F/B goes
away.  Very repeatable.

It's a Rohn 25G tower, guyed with Philly, beam at 45', 40M dipole at 43',
90' of wire runs north to act as the inverted L on the tower.  The shunt
taps at about 42' level.  It extends out about a foot or so.

Now what?  How am I going to get this to load on 160M without ruining the
pattern on 20M?  Shortening the shunt will result in an even lower R value
making it real tough to load.

I'm all ears...

Ford-N0FP
ford@cmgate.com