If the 1/2 wave element is very near the device (and resonant!) it will 
couple without a direct connection. I agree it crowds the part 15 rules, but 
the abscence of a physical connection would probably keep you out of 
trouble.

OTH, the 3 meter range you refer to is only about a wave length. A 1/2 wave 
of wire would be cumbersome in the vehical.

I have no practical solution.
John Ferrell
http://DixieNC.US

----- Original Message ----- 
From: "Mike Hord" <mike.hord@gmail.com>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Friday, January 28, 2005 5:40 PM
Subject: Re: [EE] Small FM Transmitter Antenna


>> A half wave wire will give better results. Don't try to hard wire it, 
>> just
>> run the device up & down the length of the wire.  Horizontal  vs. 
>> vertical
>> will make a difference. Insulation on the wire can make a big difference 
>> in
>> the physical dimensions of the antenna. A fat wire (Al foil) will have a
>> broader bandwidth.
>
> I'm afraid I don't understand.  Are you suggesting a T, with the
> crossbar being 1/2 wave in length and connected to the device at the
> center and formed by wires?  How close to 1/2 wave is close enough?
>
>> Placing the unit a little less than a 1/4 wave in front of a reflecting 
>> unit
>> (file cabinet?) may exhibit some gain as well.
>
> This I do understand, but it's unfortunately quite impractical.  I'd
> really just be happy with something I could hide somewhere in my car
> that would make the transmission to the antenna in the rear window a
> bit better.
>
> Mike H.
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