Hi all,

This is really an off-topic matter, but think is the real reason why I keep
subscribed to the PICLICT. Just talking about MPLAB all the day would wipe
off many guys, I'm afraid.

>
>      As far as I know it is not possible to do RDF using a whip attena, you
>      need an array of antennae that you measure the phase difference of the
>      incident signal, you use an arctan function of this information from
>      the amplitude of the recieved signals in your antenna array and out
>      pops the angle of arrival!
>
>      It is a bit more involved than that, but the maths is not too
>      horrendous to understand ... honest!

I have a brouchure from a company named "Doppler Systems, Inc"

They manufacture radio direction finding equipment using doppler system.
There is a short explanation of how it works:
" To visualize how the system works, consider a simple antenna rotating at
the end of an arm. As the rotating antenna moves toward the RF source, the
apparent frequency increases, and as the antenna recedes from the source ,
the apparent frequency decreases. This up-down (Doppler) shift occurs at the
same rate as the antenna rotates, and the phase of the shift contains the
bearing information. In a quasi-Doppler system, multiple antennas are
electronically combined to simulate a physically rotating antenna. The
pattented technique used in Doppler System's equipment combines four antenna
outputs in a smooth fashion to prevent desensitizing the receiver.

  When used with a narrow band fm receiver, the up-down frequency shift is
detected and can be heard as a 300Hz "conmutation" tone at the output. The
direction finder processes this tone to display the bearing.(Please
PicPurists look here to the PIC application niche !)

  Interaction between the four antennas causes the received signal to the
both amplitude and frequency modulated at the conmutation frequency. This
permits the system to be used with am receivers for direction finding
aircraft band signals such as ELTs"

Get more info at: Doppler Systems, Inc.
                     POBox 2780
                     Carefree, Arizona 85377
                     Tel: 602 - 488-9755
                     Fax: 602 - 488-1295

May be you can find them on the Web. Have a look in Altavista.

Have a good one.

Luis


Luis Fernandez Cormenzana
RadioBit Sistemas, S.L.

Fax/Tel:+34-6-585 64 57
e-mail: radiobit@dragonet.es
http://www.dragonet.es/users/radiobit