Patent ID: 7672411

Claim:
A radio receiver, comprising: an antenna configured to receive a radio frequency signal amplitude modulated with an audio frequency signal; a digitiser configured to sample the radio frequency signal and to generate a digital reception signal representative of the amplitude of the radio frequency signal; a demodulator configured to demodulate the digital reception signal to generate a representation of the audio frequency signal, wherein the demodulator comprises a local oscillator configured to generate a first local oscillator signal at a reception frequency of the receiver, a first mixer configured to mix the first local oscillator signal with the digital reception signal to form a first demodulated signal, and a second mixer configured to mix a second local oscillator signal with the digital reception signal to form a second demodulated signal, wherein the second local oscillator signal is at the reception frequency of the receiver and having a quadrature phase relationship with the first local oscillator signal; and a beat cancellation device configured to form a beat-cancelled signal by processing the first demodulated signal and/or the second demodulated signal to at least partially cancel from the first demodulated signal and/or the second demodulated signal a beat frequency resulting from the mixing of the local oscillator signals with the digital reception signal, wherein the radio receiver is configured for operation in a radio system in which a plurality of radio channels are transmitted at frequencies spaced apart by a predetermined channel spacing, and the demodulator further comprises a filter configured to filter the first demodulated signal, the filter having a peak response in the region of the reception frequency of the receiver and having nulls in its response in a region of frequencies spaced apart from the reception frequency of the receiver by a channel spacing.