Radio receiver with a high speed and accurate search operation and method thereof

Claim 3

A method of selecting a station for a radio receiver according to claim 1, wherein in said second frequency shift step, a frequency of said local oscillator is shifted in the direction reverse to and by the same rate as shift in the first frequency shift step.

Claim 4

A method of selecting a station for a radio receiver according to claim 1, wherein said local oscillator is a frequency synthesizer using a phase-locked loop (PLL) therein.

Claim 5

A method of selecting a station for a radio receiver according to claim 2, wherein said local oscillator is a frequency synthesizer using a phase-locked loop (PLL) therein.

Claim 8

A method of selecting a station for a radio receiver according to claim 5, wherein in said second frequency shift step a frequency of said local oscillator is shifted in the direction reverse to and by the same rate as shift in the first frequency shift step.

Claim 9

A method of selecting a station for a radio receiver according to claim 5, wherein said local oscillator is a frequency synthesizer using a phase-locked loop (PLL) therein.

Claim 10

A method of selecting a station for a radio receiver according to claim 6, wherein said local oscillator is a frequency synthesizer using a phase-locked loop (PLL) therein.

Claim 11

A radio receiver which selects a channel for those each having a prespecified frequency allocated thereto respectively, comprising: a local oscillator, a frequency shift circuit which shifts a frequency of said local oscillator, a radio receiving section provided with a filter which passes therethrough only frequencies at least within specified bandwidths, a frequency discriminator which converts a frequency outputted from said radio receiving section to a voltage, a squelch circuit which makes a determination as to whether a received signal is a desired one depending on an output voltage from said frequency discriminator, and a controller which shifts a frequency of said local oscillator with said frequency shift circuit so that as many channels to be scanned as possible will be included within the specified bandwidths, detects a desired received signal by scanning each of the specified bandwidths with the shifted frequency, scans each channel within the bandwidth where the desired received signal was detected, and changes a frequency of said local oscillator or shifts a frequency of said local oscillator with said frequency shift circuit so that the desired channel frequency identified above will be at the center of said bandwidth.

Claim 12

A radio receiver which selects a channel for those each having a prespecified frequency allocated thereto respectively, comprising: a local oscillator, a frequency shift circuit which shifts a frequency of said local oscillator, a radio receiving section provided with a filter which passes therethrough only frequencies at least within specified bandwidths, a frequency discriminator which converts a frequency outputted from said radio receiving section to a voltage, a squelch circuit which makes a determination as to whether a received signal is a desired one depending on an output voltage from said frequency discriminator, and a controller which shifts a frequency of said local oscillator with said frequency shift circuit so that as many channels to be scanned as possible will be included within the specified bandwidths, detects a desired received signal by scanning each of the specified bandwidths with the shifted frequency, scans each channel within the bandwidth where the desired received signal was detected, and changes a frequency of said local oscillator or shifts a frequency of said local oscillator with said frequency shift circuit so that the desired channel frequency identified above will be at the center of said bandwidth.

Claim 13

A frequency-modulation receiver comprising: a radio receiving section responsive to a received signal for generating an intermediate frequency signal, a frequency synthesizer responsive to a central processor for supplying said radio receiving section with a signal for selecting a predetermined channel from a plurality of communication channels, and a frequency shift circuit responsive to said central processor for supplying said frequency synthesizer with a frequency shift signal indicative of a specified bandwidth covering said plurality of communication channels.

Claim 14

A frequency-modulation receiver comprising: a radio receiving section responsive to a received signal for generating an intermediate frequency signal, a frequency synthesizer responsive to a central processor for supplying said radio receiving section with a signal for selecting a predetermined channel from a plurality of communication channels, and a frequency shift circuit responsive to said central processor for supplying said frequency synthesizer with a frequency shift signal indicative of a specified bandwidth covering said plurality of communication channels.

Claim 15

The receiver of claim 10, wherein said frequency shift circuit controls said frequency synthesizer so as to generate a further frequency shift signal for shifting the frequency of said predetermined channel to the center of said specified bandwidth.

Claim 16

The receiver of claim 10 further comprising a squelch circuit responsive to said intermediate frequency signal for supplying said central processor with information as to existence of the received signal in a scanned bandwidth.

Claim 17

The receiver of claim 10, wherein said frequency synthesizer comprises a phase-locked loop.

Claim 18

The receiver of claim 10, wherein said central processor comprises information on preselected channels to be scanned and defines an sequence of a search for the predetermined channel.