Abstract: A Computerized Mobile Two-Way Radio System is provided having microprocessor enhanced capabilities and versatility for wide area/multiple region two-way radio networks with multiple categories of users and adaptability to multiple international standards and mobile radio equipment configurations. The main elements of the system consist of (1) a microprocessor-based Control Unit, (2) a Digital Serial Interface/Link and (3) a microprocessor-based Convertible Transceiver Unit. The Control Unit provides many facilities and capabilities for the operator and the system in compact form. The Interface/Link provides a two-way path for serial data consisting of digitized audio and digital command and status signals. The Transceiver Unit is designed for operation and control over the Digital Serial Interface/Link.

Abstract: A method for scrambling speech such as in a mobile land based communication system is disclosed. Essentially, variable length time samples of digitized speech are stored and time inversion scrambled. The scrambled speech is converted back to analog form and transmitted to a receiver which reciprocates the process to reproduce the desired speech signals. Scrambling and descrambling of the speech signal is synchronized to provide corresponding sample time inversions and accurate reproduction of the speech input signal. The level of security afforded by the scrambling method may be varied by varying the length of the sampling period or by mixing forward and reverse time samples under control of an algorithm.

Abstract: A method and apparatus for filling audio blanks in a message received by a receiver resulting from switching the receiver between a plurality of input channels each having a different message for selecting the channel of highest priority is disclosed. A recording and playback device is connected between the receiver and an output channel for recording a given time segment portion of a first message. The receiver is switched to a second channel for a period of time equal to the given time segment for receiving a second message and for determining which channel has a higher priority. The recorded portion of the first message is delivered to the output channel simultaneously with the switching of the receiver to the second channel to repeat the first message portion at the output channel, thereby to fill in the audio blank resulting from switching the receiver between the input channels.

Abstract: In an amplitude modulation radio receiver a relatively narrow band filter is placed before the receiver detector and a relatively wide band filter is placed just prior to the IF amplifier stages. An IF stage controlled by receiver AGC is designed to have a saturation or clipping level about 6 dB above the normal IF level for that stage. As a result the selectivity characteristic for the receiver will be approximately rectangular and encompass the IF frequency channel if the bandpass of the narrow band filter is chosen to be the IF frequency channel.