Jim Weir - Rubber 'Baby Belly Baluns

For Jim (and kibitzers of all stripes :-):

I had a curious situation yesterday while flying my Fly Baby. An aircraft
complained that my radio was unreadable. Yet a buddy on the ground with a
aircraft-band receiver said that my radio was a bit scratchy, but perfectly
readable.

I think I'm getting bit by my antenna patterns. Both antennas are mounted
internal to the aircraft, with one being a horizontal coax-type dipole (with
baluns) mounted underneath the metal turtledeck (!) and the other being my
PVC-pipe job mounted vertically just a foot or two behind my manly back.

Right now, I have the horizontal dipole hooked to the receive side and the
vertical one to the transmit side. But they're hooked that way because of a
similar complaint I had *last* summer.

I know pattern is a problem with the horizontal one, since transmissions from
aircraft behind me are very garbled (directly in line with dipole). I think the
vertical one is ending up with a horrid pattern forward (due to the nearby
ugly-bag-of-mostly-water), which might explain yesterday's complaint.

(Note to newcomers in this saga: I'm using a Narco Escort II, which has
separate receive and transmit antennas. Unlike many radios, the Narco uses the
Nav antenna for Comm reception. It must have both antennas connected for
two-way operation.)

So... I'm starting to break down and am considering putting an antenna on the
*outside* of the aircraft. I was originally going to use your copper-tape
setup, running one arm down the landing gear leg and the other across the
fabric-covered belly, but I added a long metal belly inspection panel last year
that messes that up.

http://www.bowersflybaby.com/tech/belly_pan.html

The obvious thought it to install a conventional aircraft comm antenna on the
belly panel itself...it's about 1 ft x 3 ft and would make a very good ground
plane. But the panel is just ~.016 aluminum, supported along the edges. I'd
probably have to add a cross-brace in the fuselage to mechanically support a
full-size antenna. It would complicate removing the panel for routine
maintenance, and would get in my way when I want to sit flat on the bottom
longerons dangling my feet out the belly for working on my avionics box
underneath the control panel.

A big 'ol comm antenna would be a hassle...but what about mounting a
rubber-duckie antenna, instead? A BNC connector would let me quickly remove it
to pull the panel, and since it doesn't really require a massive ground plane, I
could mount it far enough aft that it could pick up the existing support
structure for the belly panel.

So...what d'ya think?

Follow-up question: I do my antenna switching on the ground, now, switching
coaxes between radio outputs. Are there any inexpensive switch boxes that would
let me take two RF inputs and select which antennas they connect to, without
switching cables?

Ron Wanttaja