Decode squelch circuit for a continuous tone control radio receiver

Claim 1

In a radio receiver having means to be unsquelched in response to an unsquelch signal and to be squelched in response to a squelch signal, an improved decode squelch circuit comprising: a. means adapted to be connected to said radio receiver for deriving a continuous tone therefrom that is transmitted over a system to said radio receiver; b. first means connected to said deriving means for producing a first tone signal of a first phase; c. second means connected to said deriving means for producing a second tone signal of a second phase that is shifted substantially 180 degrees with respect to said first phase; d. a first transistor having input and output electrodes; e. means connecting said first transistor input electrodes to said first means; f. means connected to said first transistor input electrodes for preventing said first transistor from responding to said first tone signal; g. a second transistor having input and output electrodes; h. means connecting said second transistor input electrodes to said second means; i. means connecting said output electrodes of said second transistor to said input electrodes of said first transistor for permitting said first transistor to respond to said first tone signal at said first input in response to said second tone signal at said second input; j. a capacitor; k. means connecting said capacitor to said output electrodes of said first transistor to charge said capacitor in response to said first transistor being prevented from responding to said first tone signal, and to discharge said capacitor in response to said first transistor being permitted to respond to said first tone signal; l. an output transistor having input and output electrodes; m. means connecting said input electrodes of said output transistor to said capacitor for causing said output transistor to produce a squelch signal in response to said capacitor being charged above a selected level and for causing said output transistor to produce an unsquelch signal in response to said capacitor being discharged below a selected level; n. means connected between said output electrodes of said output transistor and said electrodes of said second transistor for causing said second transistor to respond to second tone signals of A lower magnitude in response to said output transistor producing an unsquelch signal; o. and output means connected to said output electrodes of said output transistor for applying said squelch and unsquelch signals to said receiver.