Multichannel fm receiver

Claim 1

A pulse counting detector for frequency modulated, amplitude limited radio frequency signals, said detector comprising: a transistor having an input circuit and an output circuit; means to bias the transistor to conduct when the signal present at said input exceeds a predetermined level; a radio frequency by-pass network connected to said output circuit for converting the radio frequency output of said transistor to an audio-frequency demodulation signal; a differentiating circuit having a time constant of the order or less than one-half the period of the highest r.f. signal, said differentiating circuit being coupled to said input circuit of said transistor and responsive to said amplitude limited r.f. signals for providing said transistor input circuit with differentiated pulses which render said transistor conductive throughout a conduction on angle corresponding in duration to the duration said differentiated pulse exceeds said predetermined level; and a negative d.c. feedback network connected between said input and output circuits for shifting the d.c. level of said differentiated pulses as the frequency of said pulses increase, thereby reducing the conduction angle and current pulse width of said transistor per cycle of input signal to effect a decrease in the rate of increase of the output circuit current of said transistor per unit time as the frequency of said pulses increases whereby the a.c. transfer characteristic of said detector in the high frequency range is expanded and the slope reduced.