Transmit/receive mode protection arrangement

A transmit/receive mode control apparatus for a communication station having a microphone element for generating an audio signal for modulating the transmissions of said communication station and a "push-to-talk" switch for keying said station into the transmit mode whenever said switch is pressed, comprising:

• an audio amplifier for amplifying audio signals derived from said microphone element;
• averaging means, coupled to said audio amplifier, for establishing a signal indicative of an average audio level derived from said amplifier;
• first comparator means, coupled to both said audio amplifier and to said averaging means, for comparing the current audio signal level or a predetermined fraction thereof, with the average audio level derived from said averaging means and generating a first comparator signal whenever the current audio signal level, or predetermined fraction thereof exceeds the average audio signal level established by said averaging means;
• memory circuit means having a predetermined decay time constant associated therewith, coupled to said first comparator means, for memorizing the output signal level of said first comparator means and allowing said signal to decay in accordance with said time constant;
• second comparator means for comparing the decaying signal from said memory circuit means with a predetermined reference level and providing a reset signal whenever said decaying signal falls below said predetermined reference level;
• mode control means, coupled to said push-to-talk switch and to said second comparator means for setting said communication station (a) in the transmit mode responsive to the pressing of said push-to-talk switch, (b) in the receive mode responsive to the continued pressing of the push-to-talk switch and the presence of a reset signal, and (c) in the receive mode responsive to the release of the push-to-talk switch regardless of the presence or absence of a reset signal.

An apparatus intended for coupling a microphone element having an associated "push-to-talk" switch to a communication station operable in a transmit or receive mode, the transmit mode normally being called for by the pressing of the push-to-talk switch, said apparatus for restoring the communication station to receive mode operation in the event that the push-to-talk switch remains pressed for an extended period of time in the absence of speech into said microphone element, comprising:

• averaging means coupled to said microphone element for establishing an average audio level;
• first comparator means for comparing a current audio level with the average level established by said averaging means and providing a signal whenever the current level or a predetermined fraction thereof, exceeds the average level;
• timing comparator means, coupled to said first comparator means, for providing a reset signal whenever the current level or a predetermined fraction thereof exceeds the average level and then fails to exceed the average level for a predetermined period of time;
• mode control means, coupled to said push-to-talk switch and adapted to receive said reset signal, for setting said communication station (a) in the transmit mode responsive to the pressing of said push-to-talk switch, (b) in the receive mode responsive to the continued pressing of the push-to-talk switch and the presence of a reset signal, and (c) in the receive mode responsive to the release of the push-to-talk switch regardless of the presence or absence of a reset signal.