Can I turn a device on and off using an antenna and tuner? Do I need to amply the signal?
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.