Hello.

I am planning a tracking system using GPS. It will be made up of several parts - a 'base station' consisting of a laptop or PC, will receive the signals from varios 'clients'. The client parts will each have a GPS module and some form of transmitter.

The base station will the continually get updated with peoples/cars positions, and plot them all on a map (this isnt a priority atm!)

The problem I am having is getting a suitable transmitter/receiver that will work up to a range of up to 40 miles (if base is static). The only thing I can think of is equiping each tracking unit with a mobile phone. When the base station phones, the mobile will automatically be 'picked up' and the current GPS data sent via audio.

Do you think this will be the only feasible method of communication? Something without the cost of hundreds of 10 second calls would be nice :-)

Thanks for any info :-)