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.

FM radio receivers, particularly in moving vehicles, are subject to intermittent adjacent-channel interference. It is known to detect such interference and suppress it by narrowing bandwidth in the Intermediate Frequency (IF) signal path. However, it is desirable to again broaden the bandwidth once the interference has subsided. An improved system, which automatically and dynamically adjusts the bandwidth, employs first and second signal level evaluation circuits (11, 12), a comparison stage (13) which compares their outputs, and a variable-bandwidth filter stage (6, 14) controlled by the comparison stage. The comparison stage is programmed with a set of signal difference threshold values and corresponding filter bandwidth values, and controls the filter stage (6, 14) to adjust the bandwidth to the appropriate value, indicated by which signal difference threshold value has been exceeded. In a preferred embodiment, a second IF filter (15) does "double duty" as part of the variable-bandwidth filter stage.

In this radio receiver, the charge on a capacitor (14) controls the bandwidth of filters in the receiver's audio circuits. When tuning the radio, a bandwidth control circuit (13) forces this capacitor (14) to discharge, thereby forcing the audio path to be bandwidth restricted, thereby minimizing interstation noise reproduction.

In an FM receiver where the center frequency of an IF filter is varied depending on the received signal, an arrangement is described where the bandwidth of the variable IF filter is changed depending on reception quality of the received signal.

The invention relates to a method for the control of the bandpass width in the filtering of an intermediate frequency signal of an audio receiver of a radio reception apparatus. A signal parameter of a user signal of the audio receiver which is received at a reception frequency is determined and taken into account and a signal parameter of at least one neighboring signal which is received at a neighboring frequency which is adjacent to the reception frequency is determined. The bandpass width of the intermediate frequency filtering is selected in dependence at least on the signal parameter which is determined from the user signal, on the signal parameter which is determined from the neighboring signal and on the frequency distance between the reception frequency and the user frequency. Furthermore, the invention relates to a corresponding radio reception apparatus.