Abstract: A variable rate tuning circuit of the type which may be used to control the frequency of transmitters, receivers, and transceivers includes a manually rotatable dial (15) connected to a pulse generator (20) the output of which produces pulses directly proportional to the amount of dial rotation. These pulses are applied directly to a frequency determining counter (10), and the pulse rate is such that fine resolution over the frequency of the device may be obtained directly from rotating the dial slowly. Large changes in frequency may be made by rotating the dial rapidly. The output pulses pass through a differentiator (40), and integrator (30) to a voltage-to-frequency converter (35). The faster the dial is rotated, the larger will be the analog voltage output of the integrator, thus the higher the output frequency of the converter (35). The output of the converter is also applied to the frequency determining counter (10).

Abstract: A heat sink (50), on which is mounted heat producing elements, such as transistors (40-43), is contained entirely within a cabinet (10) provided with openings (20, 27) positioned directly below and above the heat sink. The heat sink includes a rectangular plate (52) with the transistors mounted on one side and a plurality of integrally formed parallel fins (60) projecting laterally from the plate on the other side and extending diagonally thereacross. The heat sink may be convection cooled by air entering the openings (22) in the bottom of the cabinet and exiting through openings (27) in the top, or the heat sink may be forced air cooled by means of a fan (75) mounted the rear panel (16) which draws air through the openings (22) and across the fins (60).

Abstract: A single-sideband radiotelephone system includes a single-sideband transmitter which initially broadcasts two frequency-spaced tones simultaneously for a predetermined time interval, and thereafter broadcasts the two tones alternately in a unique code pattern to access a predetermined receiver. Each single-sideband receiver in the system includes a pair of detectors each having a narrow bandpass, the center frequencies of which are spaced apart by the difference in frequency of the transmitted tones. The center frequencies of the detectors are simultaneously varied relative to the initial two-tone broadcast while maintaining the frequency differential therebetween; and simultaneous detection of both tones will terminate the frequency varying mode of operation. The subsequently transmitted unique code pattern is then sensed by the detectors, the code pattern decoded, and the selected receiver is enabled to receive any subsequently broadcasted information.