Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Patent
1990-09-14
1993-05-18
Eisenzopf, Reinhard J.
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
4551642, 4551651, 455222, 455265, H04B 126
Patent
active
052128172
ABSTRACT:
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.
REFERENCES:
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patent: 5005209 (1991-04-01), Kung et al.
patent: 5014348 (1991-05-01), Boone et al.
patent: 5020141 (1991-05-01), Meszko
Eisenzopf Reinhard J.
Keough Timothy H.
Rickert Roger M.
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