One big problem right off the crack of the bat. "Folded" dipoles have a
characteristic feedpoint impedance of something on the order of 300 ohms. A
standard dipole at the center of resonance will have a characteristic feed
point impedance of something on the order of 72 ohms.

The mismatch for a 50 ohm radio (without some sort of a transformer) to 300
ohms is a hell of a lot more than 72 ohms.

Somebody posted that a folded dipole has a broader bandwidth than a straight
dipole. I do not believe that to be true. The main use for folded dipoles
without transformers was in the 1950s when we made them out of twinlead and
fed a TV set with them. TV sets in those days were designed for 300 ohm
antennas.

Get yourself a 3/8" diameter wooden dowel 48" long. Get two pieces of
copper tape 21.5 inches long. Glue the tape to the dowels so that there is
a 1/4" gap in the center of the dowel between the pieces of tape. Run the
tape out as far as it will go towards the end of the dowel. You should have
about 2" of bare dowel at each end of the dowel.

Drill an 1/8" hole into each of the pieces of tape right at the center ends
of the tape. Take a piece of 50 ohm coax cable (RG-58 from the spool in the
back of the Radio Shack store) and peel back the black outer jacket for an
inch. Now fish the center white/clear insulator through the braid by means
of an icepick or similar tool. Twist the braid tightly and poke it through
one of the 1/8" holes. Solder the braid to the copper foil. Strip the
white/clear insulation from the center conductor for about 1/4". Poke the
center conductor/insulation through the remaining 1/8" hole. Solder the
center conductor to the copper tape as it exits the hole.

As close to the braid as possible, run a tie-wrap around the black outer
sheath of the coax and fasten it securely to the dowel. Now run that coax
at right angles for at least a foot or two before snaking it around through
the airframe.

You've got two inches on either end of the dowel to nail, screw, glue, or
otherwise fasten your dipole antenna to one of the fuselage formers aft of
the baggage compartment. Keep the TIPS of the antenna as far away as you
can from any metal.

Some refinements: A balun is always a good idea when connecting a BAL anced
antenna (dipole) to UN balanced coax cable. You can do this with little
tiny chunks of powdered ferrite called toroids, or you can do this with a
coax "split-tube" design. Both are a little beyond the scope of a newsgroup
article.

Since I absolutely refuse to use the newsgroups to pimp my own goods, will
somebody else please tell this fellow where he can get copper tape, toroids,
and the illustrated book that shows how this all works?


Jim




"Terry" wrote in message
om...
I'm wanting to put an antenna inside the fuselage of my Aeronca Champ.
I've read about the folded dipoles, and wondered if this was
something that would be feasible. I want it for communications with
my handheld. Any thoughts?

Thanks!

Terry
Gordonville, MO