Automatic input attenuator for h.f. communication receivers

The final selectivity of a communication receiver is generally determined by the bandwidth of the i.f. filters. When the a.g.c. of the receiver is determined only by the signals passing these filters, severe overloading of the relatively broadband h.f. gain stages may occur. Reducing this risk of overloading requires a broadband attenuator at the input of the receiver. The attenuation should be dependent on the signals passing the i.f. filters as on all other signals reaching the h.f. gain stages, but not the i.f. amplifiers. Such an automatic attenuator system is discussed, and its design philosophy presented.