| 摘要 |
66446-474 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 to produce a sync detect signal. In response to the 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 signals 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. |
