The shield on the headphone cable is used as the antenna for such devices.
As for matching, how good of a match can a headphone cable be? Inside most
radios the connection is a single cap, in the pF range, between the jack and
the RF front end. Oh, and some kind of choke for DC continuity for the
audio part. Strip away some of the plastic jacketing around cable at the FM
radio end, and solder on an extra wire to the shield. Route the wire some
place convenient. You'll have to experiment for best reception. Just keep
it away from any noise and power sources, like spark plugs, transmitters,
Illudium P-36 Explosive Space Modulators.

Life's a highway -- get on and ride,
Robert N3LGC


"Ken C" wrote in message
...
I am tryng to use a Sansa M240 MP3 player and FM radio on my
motorcycle, with the output going into a helmet sound system
(Starcom1). This means that the headphones -- which usually act as
the FM antenna -- will not be used.

I would like to try using a splitter on the headphone jack, with one
leg to the helmet sound system and the other leg to an antenna. My
first thought was a simple 1/4-wave dipole to run around the fairing
perimeter. Would that work? Would I need to add some passive
components or some matching because the device expects the headphones
to be the antenna?

And, Yes, the Starcom1 also interfaces to a TH-F6A tri-bander.

Ken KC2JDY