In time domain, if two signals are presented simultaneously, they will add up and mix, therefore they can not be distinguishable. Therefore in order to transmit more that two signal (programs) via a common medium (air) we need certain separation of bands. This is provided by a technique called FDM (Frequency Division Multiplexing). First of all, as said before, any transmitting signal has to be modulated for all those good reasons. When the frequency carriers are selected differently, this separation of bands will be provided, not in time domain, but in frequency domain. In order to be sure that the participating signals do not overlap in frequency domain, a security margin must be taken into consideration.

When the separation of bands is considered they can be multiplexed and mixed without any problem of recovery. Then they are transmitted after amplification via the sender antenna.

The transmission waves travel in the air in all directions (actually not exactly in all direction, depending on the directionality of the antenna) and will be collected by the antenna of your radio at home or elsewhere. The antenna collects the receiving signals (which are very small I amplitude, in the range of a few millivolts to microvolts). The received signals must be first preamplified and recovered from noises, then will be filtered. This is done by the tuning operation you perform. When you search for a special sender program, you tune the radio to that frequency, e.g., 108 MHz, therefore the upper and lower limits of bandpass filter will vary by your tuning action. Since the actual data is in analogue form, there is no need to perform decoding, binary decoding, and digital to analogue conversion (unless in digital radios). Therefore afterwards, the filtered signal is demodulated and amplified and delivered to the loudspeaker system. The schematics of the whole process has been shown in a very simple language as follow: