Hi - I was just thinking about this. How does a device in real time share an antenna between rx and tx circuits? I'm thinking of something like a cell phone, for example. My first thought was that the device would allot a certain amount of time for sending and a certain amount of time for receiving (say, every other 5 microseconds, or something like that). But then making every other device match up with that would be rather difficult methinks. So then my next idea was that the device is always both sending and receiving and the received signals are just extracted from the antenna's signal. But then I got to thinking about exactly how this would be done. You'd want to subtract the signal being transmitted from the overall signal present at the antenna - but where would you be getting the antenna signal? Wouldn't you be getting it from the antenna connection, where the transmitter circuitry is connected to the antenna? So how would you be able to pull out the rx signal?
I suspect this is a terribly uninformed question, but I'm really a robotics/sensors guy - all this RF stuff seems like black magic to me :)
-Michael