DIYbanter - View Single Post - Using headset as cell phone radio antenna.

Terry Casey

In article ,
says...

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.

But if the 2nd ring is ground, the shield should be connected to it ...

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.

.... which connects the shield of a 3-pin plug to 'ground' - which also
doubles as the antenna connection, as you have proved ...

--

Terry