chapter  4
3 Channel spacing
Pages 1

VHF systems. Note how the 8.33 kHz system of

channel spacing allows three DSB AM signals to

occupy the space that was previously occupied by

a single signal.

The disadvantage of narrow channel spacing is

that the guard band of unused spectrum that

previously existed with the 25 kHz system is

completely absent and that receivers must be

designed so that they have a very high degree of

adjacent channel rejection (see page 48). Steps

must also be taken to ensure that the bandwidth of

the transmitted signal does not exceed the 7 kHz,

or so, bandwidth required for effective voice

communication. The penalty for not restricting

the bandwidth is that signals from one channel

may ‘spill over’ into the adjacent channels,

causing interference and degrading com-

munication (see Figure 4.7).