On Sat, 28 Jul 2012 11:46:03 -0700, Jeff Liebermann
wrote:

Wrong! The shield is used as the antenna!
(...)
If I have time, I'll play with a connector and see which pin is the
antenna.

Well, you're 1/2 right (and I'm half wrong). The antenna is NOT the
shield but the shield is not the ground connection on the 3.5 mm
connector.

I inserted a 4 pin 3.5mm plug into my Droid X, and setup the FM tuna
to play through the speakers. Using a 2ft long clip lead as an
antenna, I probed all 4 pins on the connector to see what it could
hear. The sleeve (shield) connection did nothing and was the same as
no antenna. I couldn't even hear a local strong station. The tip and
the first ring picked up a few stations. However, the 2nd ring
connection produced dozens of stations (along with their RDS data), so
that must be the antenna wire.

http://encyclopedia2.thefreedictionary.com/Tip+Ring+Sleeve
It's the TRRS connector, with connections marked as:
tip, ring 1, ring 2, and sleeve.
http://i4.photobucket.com/albums/y136/invinciblegod/TRRSConnector3.png
The typical wiring configuration is:
tip Left Earphone
ring 1 Right Earphone
ring 2 Ground
sleeve Microphone

If you plug a 3 pin TRS (tip-ring-sleeve) connector into a 4 pin TRRS
jack, ring 2 and the sleeve are connected together, thus grounding the
microphone connection.

The mic connection is also uses for controlling the music player:
http://www.wisebread.com/build-a-cable-to-control-your-android-phone-while-you-drive




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558