| 摘要 |
A decoder circuit responds to a given code to provide an enabling signal for rendering an audio circuit operative. A push-button switch actuatable to monitor the channel is associated with timer and electronic switch. One connection places the receiver in either a monitor mode or a tone-squelch mode. A second connection places the receiver in condition to be unsquelched manually or by the carrier wave or by the proper code. The battery saver provides a continuous supply voltage during the first tone, the entirety of the code and for a time thereafter. The rate of the pulsed supply voltage produced after such time will be increased. Alternately, the receiver can be placed in the carrier-squelch mode. The receiver can be reset to the code-squelch mode and cause the pulsed supply voltage to revert to its usual rate. After the start of detection, pulses render ensuing circuitry nonresponsive to glitches. A tone signal of at least a predetermined duration produces an enabling signal commencing with the termination of the first tone. There is produced an alerting tone having characteristics corresponding to the duration of the second tone. In the absence of a control signal, the output of a gate that feeds the audio circuit floats so as not to be a load. A long first tone enables all receivers in the group. A multiple tone receiver is readily connected to a single tone receiver. The timing functions in the receiver are performed by the resettable divide-by-two circuits. |
