Thanks jiripolivka for your detailed reply.... First, I didnt quite know that wireless transmission beyond 500 Meters will involve legal issues.... Will check that out... However, the two locations between which I need the signals to fly may be less than that distance... It was just an offhand guess, that its 500 meters.... The aerial distance may be less by a 100-150 odd meters....
I was just thinking to make a FM Transmitter Circuit - available so freely on internet.... And using that circuit, I was planning to ROUTE the power supply to the circuit thru the contact of the Relay whose status is to be read....
So when the contact is OPEN, there's no power to the FM Transmiiter and the FM Transmitter is 'dead'; so there's no transmission.... When the Relay contact state CLOSES, the FM begins to transmit at a certain frequency....
The receiving side will be tuned to receive these transmissions....!! So when there IS a transmission, the receiver instead of sending the received signal to an audio speaker, would send it to a Relay Coil after conversion to DC and signal conditioning and light the Lamp....
Can you guess, if this concept will work or I am just wasting my efforts....
...