The Limiter

Author: J.B. Hoag

In order to eliminate any possible variation in the amplitude of an f.m. signal before it is detected, a circuit called a "limiter" is used. The strength of the input voltages to this stage are so great that they saturate the tube, and the tops and bottoms of the waves are clipped off. A circuit of this type was described in Chapter 30 for the generation of a square wave. In the present case, however, the plate circuit contains a tank circuit which resonates sharply to the carrier wave and its accompanying band of frequencies. Thus the harmonics, produced by cutting off the tops of the waves, are not emphasized (by resonance) and do not pass on to the next stage in the receiver. Fig. 33 D shows a typical limiter circuit.

Fig. 33 D. An f.m. limiter circuit