I would like to use a radio receiver to turn a device on and off.
The idea is that when the signal is received, the device is turned on, and when the signal stops, the device turns off.
I want to use an antenna and a tuner to receive the radio signal.
I am assuming these components are all that is needed to receive the signal, and that amplification of the signal is not necessary – is this correct? If the device is turned on by detecting the presence of the signal, and turned off by detecting its absence, is it necessary to process the signal (i.e. amplify, demodulate) once detected?
As long as the signal is received, will it matter how strong/weak it is?
Best Answer
It is possible to use the power of the transmitted signal to run something, as long as you keep in mind that this power will be very limited. A "crystal radio" works on this principle. The power driving the headphones actually comes totally from the received radio signal.
With a sufficiently strong signal and good antenna, you should be able to rig up something like a crystal radio that turns on a transistor when the demodulated amplitude is high enough. There are various options, but ultimately power from elsewhere will have to make use of the transistor that is turned on/off directly by the received radio signal.