Multifrequency superheterodyne receiver with priority channel monitoring

Claim 1

A receiver of the superheterodyne type for receiving radio wave signals on a predetermined number of channels, at least one of which is designated a priority channel while others are nonpriority channels, said receiver comprising in combination: first circuit means operative to provide reception of a signal on said nonpriority channels; second circuit means operative to provide reception of a signal on said priority channel; means for producing an automatic gain control signal, said automatic gain control signal varying from a first controlling level during reception of any one of said signals to a second controlling level during the reception of no signal; switching means coupled to said first and second circuit means and having at least first and second conditions of operation, the first condition being wherein the first circuit means is made operative and the second condition being wherein the second circuit means is made operative; pulse generating means for providing to said switching means pulses having first and second output levels, said first output level causing the switching means to operate in the first condition and said second output level causing the switching means to operate in the second condition; means for detecting the reception of a priority channel by the second circuit means in response to the variation of the automatic gain control signal to the first controlling level during a period in which the pulse generating means produces the second output level; and means responsive to the detection of the detecting means for locking the pulse generating means to inhibit the generation of pulses and to continually produce the second output level.