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

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

On Fri, 17 Feb 2006 04:27:04 GMT, "SignalFerret"
wrote:

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.

Hmm. Well, the shield on the shielded stereo cable between the player
and the helmet sound module might pick up some interference from the
motorcycle's electrics. What components would you suggest that I
install on that cable to filter that out? Basically, I would want to
filter out everything that is not audio frequency (20 Hz - 20 kHz) or
between 88-108 MHz.

The player headphones have a main cable that is 29" long before
splitting to each headphobne. This is 1/4 wave for FM BCB. I could,
as you suggest, splice in a 29" wire at the player end of the cable.

Ken KC2JDY

I wouldn't over think it too much. Try just a floppy wire 18 inches or so,
and see what noise it picks up? You're bigger problem is those radios
aren't designed to pick up distant stations, so outside of a large metro
area you might not get any reception, or worse a signal that constantly
fades in and out. Try the simplest solution first, then start adding
pieces.

Robert N3LGC

"Ken C" wrote in message
...
On Fri, 17 Feb 2006 04:27:04 GMT, "SignalFerret"
wrote:

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.

Hmm. Well, the shield on the shielded stereo cable between the player
and the helmet sound module might pick up some interference from the
motorcycle's electrics. What components would you suggest that I
install on that cable to filter that out? Basically, I would want to
filter out everything that is not audio frequency (20 Hz - 20 kHz) or
between 88-108 MHz.

The player headphones have a main cable that is 29" long before
splitting to each headphobne. This is 1/4 wave for FM BCB. I could,
as you suggest, splice in a 29" wire at the player end of the cable.

Ken KC2JDY