Freq (kHz)

Fig. 3.21. (a) Telephone multiplexing (b) FDM in telephone transmission.

These modulated carriers are all amplified and transmitted together over the channel. Analog FDM used extensively in point to point microwave radios, coaxial cable wire line system and fiber optic transmission (Wavelength division multiplexing).

FDM Hierarchy. To standardize the equipment in the broad band transmission system. CCITT recommended the following FDM hierarchy.

Table 3.6. FDM hierarchy recommended by CCITT


Number of




voice circuits

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