Abstract: An arrangement for reducing the amount of battery supplied power to a high frequency synthesizer. The phase-locked loop section of the synthesizer is periodically disconnected from the battery supplied power. In order to prevent substantial drift of the phase-locked loop during such power interruption, a control signal is provided for maintaining the VCO frequency. By minimizing the frequency drift, the loop can be re-locked in a short period of time following each power interruption.

Abstract: A digital circuit for sensing a frequency component F.sub.0 in an applied signal. The amplitude of an input signal is sampled at a clock rate that is N times F.sub.0 and each amplitude sample is encoded as a digital word. The digital words are applied to a first input of an adder, and digital feedback words are applied to a second input of the adder. The output of the adder is applied to a delay circuit which delays the adder output an integral multiple of one-half of the period T.sub.0 corresponding to frequency F.sub.0. The delayed words are multiplied by a constant K whose magnitude is less than one and greater than zero. The delayed and multiplied words are applied as the feedback words to the second input of the adder in phase with the encoded words applied to its first input. A circuit output signal is derived from the adder output, or from the delay circuit output.

Abstract: The prior art tone detector shown in U.S. Pat. No. 3,962,645 provides a repetitive sequence of vector signals at a predetermined or selected rate determined by the desired tone frequency to be detected. Each vector in the sequence has a different phase or angular direction. One vector in each sequence is selected at a time corresponding to a selected (usually zero) point in each cycle of received tone frequency. If the sum of a number of selected vectors exceeds a threshold, an indication of the desired tone is provided.In some tone detectors a phase shift in the tone can indicate a selected condition. Such a phase shift is detected by counting the number of vectors which are produced after the phase shift, whose magnitude added to the magnitude of the vectors produced before the phase shift exceeds a threshold, and whose sign differs from the sign of the vectors produced before the phase shift. When the count reaches a predetermined number, a phase shift indication is provided.

Abstract: A radio transmitter power amplifier is connected to a driver circuit whose drive power determines the output power of the power amplifier. Direct current is supplied to the driver circuit under the control of a temperature control circuit which compares a temperature indicative voltage with a voltage indicative of the direct current drawn by the power amplifier. If the power amplifier direct current is above a desired level for a given temperature, the control circuit reduces the direct current supplied to the driver circuit, and hence reduces the output power of the power amplifier. If the power amplifier direct current is below a desired level for a given temperature, the control circuit increases the direct current supplied to the driver circuit, and hence increases the output power of the power amplifier.

Abstract: Many radio continuous tone controlled squelch systems use a digitally generated tone. A digital adder is provided for the digital tone generator to introduce a phase shift to the tone to indicate that a radio transmission is ending.