ABSTRACT
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).
