For separating channels in FDM, it is necessary to use Bandpass filters
A bandpass filter is an electronic device or circuit that allows signals between two specific frequencies to pass, but that discriminates against signals at other frequencies. Unlike the low pass filter which only pass signals of a low frequency range or the high pass filter which pass signals of a higher frequency range, a Band Pass Filters passes signals within a certain “band” or “spread” of frequencies without distorting the input signal or introducing extra noise.
Frequency Division Multiplexing (FDM) Frequency-Division Multiplexing (FDM) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. It is analog multiplexing technique. ... FDM multiplexing technique is based on orthogonality of sinusoids.
The modulation can be AM,SSB, FM or PM . The modulated signals are then added together to form a composite signal which is transmitted over a single channel . The spectrum of composite FDM signal has been shown in fig.1 . Generally, the FDM systems are used for multiplexing the analog signals .