Hello all,

I'm trying to make a carfinder, where a pocket-sized, keyring-attached
transmitter sends a signal to a car, the car sends a reply, and the
carfinder shows some kind of signal strength indication. Do this as
the operator turns in a circle, and he should have an idea of where he
left his car in the carpark.

In Australia, it is legal to use 150MHz for any purpose, so long as the
output is limited to 100mW. I've found a pre-made transmitter unit for
that frequency and power (which gets 10km with a good antenna), but I'm
a novice to radio in general and am looking for pointers to information
on choosing the right kind of antenna to that is small enough to fit.

In the car, I don't have much more space (I could use the car's antenna
instead), but it would need to be omnidirectional.


Thankyou for your time.
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