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Old March 15th 06, 11:56 PM posted to rec.radio.amateur.antenna
Dan Andersson
 
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Default compact antenna for short range direction finding

Snide wrote:

Hello

I wand to build a short range direction finding equipment (say 200m), and
I wonder what kind of antenna would be the simplest and best for that.
the frequency will probably be around 868MHz.
the precision needs not to be very high (30°).
the antenna will be mounted on a car, and should be as small as possible.
The equipment will be mainly used in an urban environment.

Thanks for any help, tip or link

Denis


As the wavelength is fairly low, I suggest you build a 6 * 1/4 wave antenna
array and mount it on a roofrack. You can easily build a direction finder
by phaseshifting the array with a pack of pin diodes.

This method is widely used for tracking vehicles.

Directivity... 868MHz is still a long wavelength for any exotic and
directive antennas. But why not try building a loop yagi in a plastic tube.
Use PCB FR4 with plastic foam as spacer between the radials.

But still, a 4 or 6 antenna array on a roofrack seems to be enough to catch
stolen vehicles in the UK...


Cheers


Dan / M0DFI