Radio receiver having improved signal-to-noise ratio for receiving voice and data signals
First Claim
1. A receiver comprising:
- receiver means for receiving a radio frequency (RF) signal to produce a received RF signal;
frequency converter means for frequency converting said received RF signal into an intermediate frequency (IF) signal;
variable fitler means for extracting said IF signal from the output of said frequency converter means;
demodulator means for demodulating the output of said filter means to produce a demodulated signal;
sync detector means for detecting a sync signal in said demodulated signal to produce a sync detection signal;
field detector means for detecting an electromagnetic field strength of said received RF signal to produce a field detection signal; and
control means responsive to said sync and field detection signals for controlling the bandwidth of said variable filter means.
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Accused Products
Abstract
A radio receiver having a frequency converter which frequency converts an RF signal into an IF signal. An IF filter filters the IF signal to provide the filtered output to a frequency discriminator. The discriminator frequency discriminates the filtered IF signal to produce a baseband signal. From the baseband signal, a voice signal is recovered and a data signal is extracted. Using the IF signal, a field detector detects an electromagnetic field strength of RF signal and outputs a signal detect signal when the field strength is higher than a predetermined level. A sync detector detects a sync signal in the extracted data signal and sync detect signals, a controller controls the bandwidth of IF filter so that the S/N ratio of the recovered voice signal is increased and the error rate of the extracted data signal is decreased. The signal detect signal may also be obtained by a noise detector which detects the level of a noise component extracted from the baseband signal and outputs the signal detect signal when the level of noise component is higher than the predetermined level. The frequency of the extracted noise component is positioned adjacent to the higher portion of the voice frequency band.
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Citations
28 Claims
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1. A receiver comprising:
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receiver means for receiving a radio frequency (RF) signal to produce a received RF signal; frequency converter means for frequency converting said received RF signal into an intermediate frequency (IF) signal; variable fitler means for extracting said IF signal from the output of said frequency converter means; demodulator means for demodulating the output of said filter means to produce a demodulated signal; sync detector means for detecting a sync signal in said demodulated signal to produce a sync detection signal; field detector means for detecting an electromagnetic field strength of said received RF signal to produce a field detection signal; and control means responsive to said sync and field detection signals for controlling the bandwidth of said variable filter means. - View Dependent Claims (2, 3, 4)
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5. A receiver comprising:
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means for receiving an RF signal to produce a received RF signal; frequency converter means for frequency converting said received RF signal into an IF signal; filter means for filtering the output of said frequency converter means to extract said IF signal therefrom; demodulator means for demodulating the output of said filter means to produce a baseband signal; frist detector means for detecting a specific signal out of said baseband signal to produce a first detect signal; second detector means responsive to the output of said frequency converter means for detecting whether a received level of said RF signal is higher than a predetermined level and for producing a second detect signal when said received level is higher than said predetermined level; and control means responsive to said first and second detect signals for controlling the bandwidth of said filter means. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A radio receiver comprising:
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frequency converter means for frequency converting a radio frequency (RF) signal into an intermediate frequency (IF) signal; filter means for filtering said IF signal to produce a filtered IF signal; demodulator means for demodulating said filtered IF signal to produce a baseband signal; first detector means for detecting a sync signal from said baseband signal to produce a first sync detect signal; second detector means responsive to said filtered IF signal for detecting an RF signal whose level is higher than a predetermined level, to produce a second detect signal; means for narrowing the bandwidth of said filter means in response to a first combination of said first detect signal and absence of said second detect signal. - View Dependent Claims (18, 19, 20, 21)
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22. A method of controlling a bandwidth of an intermediate frequency (IF) filter within a radio receiver, comprising the following steps of:
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receiving a radio frequency (RF) signal to produce a received RF signal; frequency converting said received RF signal into an IF signal; filtering said IF signal to produce a filtered IF signal; demodulating said filtered IF signal to produce a baseband signal; detecting a specific signal out of said baseband signal to produce a first detect signal; responsive to said IF signal, detecting an RF signal whose level is higher than a predetermined level to produce a second detect signal; and responsive to said first and second detect signals, controlling said bandwidth. - View Dependent Claims (23, 24, 25, 26, 27, 28)
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Specification