some other little tidbits to add to this discussion....
 The match between the aerial and the surrounding space is also
 important to the effeciency of the aerial.  The effeciency of
 a given antenna (aerial) can be improved to a point by making
 the elements as large as practical given the constraints of the
 frequency and the bandwidth allowable.   Also, the height above
 the terrain is an important factor.  Generall speaking, the
 higher, the better.  But, there is a practical limit.  And, the
 material the antenna is made of is somewhat important to
 effeciency.  And, I agree with what Lance said below.  There
 are many many volumes of information and antenna theory out
 there.  The web is a good place to look.  Especially at HAM
 Radio sites.  You'll find a wealth of information here.

                                          Good Luck,


                                             Jim


On Mon, 20 March 2000, Lance Allen wrote:

>
> >
> > Now how you convince the high frequency signals in your circuit to just
> > shoot off into free air?  I mean, HOW DO YOU TRANSMIT?!?
> >
>
> Thats a good question...
> Radio is my brackground... qualifications and all that...
> and its a bit of a mystery to me to. What you are doing
> with a transmitter is taking electricity from your power
> source and putting it into the air/ space whatever.
> The device we use for this is an aerial which is an
> efficient interface between the air and the circuit.
> Maximum power transfer from the aerial to the air will
> occur when the aerial is matched to the impedence of the
> transmitter (with losses).
> Radio waves are both electric and magnetic so if you use
> an open ended wire you are utilising the electric
> component to match with, if you use a loop you are
> matching with the magnetic component.
>  So there are certain lenghts of aerials that we can use
> dependent on the frequency we are transmitting and how
> efficient we want our aerial to be. ..... its a big topic that
> is covered by a huge array of books but a good start is to
> connect a 1/4 or 3/4 wavelenght aerial to your output.
> Wavelenght(metres) = speed of light(300,000Metres/Sec)
>  / frequency.
> _____________________________
>
> Lance Allen
> Technical Officer
> Uni of Auckland
> Psych Dept
> New Zealand
>
> www.psych.auckland.ac.nz
>
> _____________________________

jim@jpes.com