There is no such big differences between a light emitting (LED) and a light receiving diode (photodiode), they are just the reverse of each other. In fact photodiodes can even emit light, but very inefficiently. Same in reverse, LEDs can also detect light, just badly.
It seems like most efficient energy conversion methods can be used in both directions.
Yes, but you would blow out most of the amplification circuitry in a radio telescope reciver if you tried to use it for broadcast at any kind of power.
There is no such big differences between a light emitting (LED) and a light receiving diode (photodiode), they are just the reverse of each other. In fact photodiodes can even emit light, but very inefficiently. Same in reverse, LEDs can also detect light, just badly.
It seems like most efficient energy conversion methods can be used in both directions.
Yes, but you would blow out most of the amplification circuitry in a radio telescope reciver if you tried to use it for broadcast at any kind of power.