Abstract: To transmit encoded information such as for example voice messages between remote transceivers, a transmitter digitizes and encodes an audio signal and then transmits the resulting digital coded signal to the receiver. The receiver decodes the signal and converts it back to an audio signal. The received encoded digital signal is used to reset the timing clock in the receiver so that the timing is synchronized in the receiver and transmitter by the transmitted encoded information. The encoder transmits digital information to a shift register. Encoding switches select certain stages of the shift register and the transmitter transmits the exclusive-OR of the digitized message and the output of the selected stages. This signal is also the input to the shift register. The information transmitted to the receiver is a scrambled digital signal.

Abstract: An inexepensive diversity receiver compares the received signal strength signal with a threshold value. When the received signal falls below the threshold value a signal is transmitted through a conductor and a delay circuit to a NAND gate. If the signal is applied to the the two inputs of the NAND gate at the same time, the output of the NAND gate switches a bistable flip-flop which in turn connects or disconnects a second antenna that is 180 degrees in phase from the first antenna between a state in which the signals from the two antenna is combined and a state in which they are not combined and only one antenna applies signals to the receiver.