Other

Uniden America Corporation

Noel D Atkinson

Ben F McCormick

William B Ahlemeyer

A high speed scanning radio has conventional RF amplifier, a mixer, a frequency synthesizer for the generation of local oscillator signals, an IF amplifier, a demodulator, and an audio output stage. The receiver includes a memory for storing a plurality of frequency codes corresponding to respective radio channels and a scan control for reading those codes, two for each channel, into the frequency synthesizer. A linear combination of each pair of distinct frequency codes is utilized to generate a local oscillator signal. Utilization of fractional N frequency synthesis is also disclosed. A squelch circuit including a multi-order analog highpass filter, noise diode detector, a multiplexer, an analog to digital converter, and an arrangement for storage of successive average values of noise, and for comparing those successive noise values with one another to provide a noise difference and for comparing successive noise differences with a predetermined squelch control value, detection of the presence of a signal on a channel being indicated when successive noise differences exceed the predetermined squelch control value. The squelch circuit disables the audio output stage in the absence of a detected signal on any one of the channels corresponding to said sequentially read pair of frequency codes, and the squelch circuit is deactivated and the scan control interrupted upon detection of the presence of a signal on a channel.

Scanning receiver with direct digital frequency synthesis and digital

A high speed scanning radio has conventional RF amplifier, a mixer, a frequency synthesizer for the generation of local oscillator signals, an IF amplifier, a demodulator, and an audio output stage. The receiver includes a memory for storing a plurality of frequency codes corresponding to respective radio channels and a scan control for reading those codes, two for each channel, into the frequency synthesizer. A linear combination of each pair of distinct frequency codes is utilized to generate a local oscillator signal. A squelch circuit including a multi-order analog highpass filter, noise diode detector, a multiplexer, an analog to digital converter, and an arrangement for storage of successive average values of noise, and for comparing those successive noise values with one another to provide a noise difference and for comparing successive noise differences with a predetermined squelch control value, detection of the presence of a signal on a channel being indicated when successive noise differences exceed the predetermined squelch control value. The squelch circuit disables the audio output stage in the absence of a detected signal on any one of the channels corresponding to said sequentially read pair of frequency codes, and the squelch circuit is deactivated and the scan control interrupted upon detection of the presence of a signal on a channel.

Ultra high speed scan system

A high-speed, multi-band scanning radio receiver. A frequency synthesizer loaded with a digital code read from memory performs band switching and supplies tracking signals and a local oscillator signal to multi-band RF amplifier and mixer circuitry. An output of an FM detector in the receiver is connected to a squelch circuit which includes a high-pass filter network and a diode detector, with the diode detector output being connected to an internal A/D converter of a microprocessor which converts multiple samples of the incoming signal to digital values and generates a mute signal when the average value of the converted samples is below a predetermined squelch level. An output line from the FM detector to audio output circuitry in the receiver is grounded in response to the mute signal. The microprocessor is also programmed to control receiver tuning during SEARCH mode such that searching continues until the demodulator output signal for an active channel is substantially in the center of the demodulator S curve, as detected by a window detector.

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Indianapolis, IN, United States of America

Noel D Atkinson