could anyone tell me how an AM receiver antenna works? actually its height should be be very high,isn't it? but,it is very compact. can we design an FM antenna in the same way. if so please tell me how to do it.
Most AM broadcast band antennas are loop types. You do not need an efficient antenna because the atmospheric noise is orders of magnitude larger that the semiconductor noise of the receiver.
Well, it is basically a big inductor wound around a ferrite rod, and has a series capacitance to resonate it at one frequency. When you change radio stations in an AM antenna, the capacitance value is changed so that the inductor is resonated at the desired frequency. In other words, it is very narrow band and needs to be tuned to cover the entire AM radio broadcast band.