| 主权项 |
1. A radio receiverid="REI-00002" date="20150331" ,id="REI-00002" id="REI-00003" date="20150331" 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, the radio receiver id="REI-00003" 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 radio 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 radio receiver and having a quadrature phase relationship with the first local oscillator signal, wherein the demodulator further comprises a filter configured to filter the demodulated signals to thereby generate first and second filtered demodulated signals, the filter having a peak response in the region of the reception frequency of the radio receiver and having nulls in its response in a region of frequencies spaced apart from the reception frequency of the radio receiver by the predetermined channel spacing; and a beat cancellation device configured to form a beat-cancelled signal by processing the first filtered demodulated signal and/orand the second filtered demodulated signal to at least partially cancel from at least one of the first filtered demodulated signal and/orand the second filtered 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. |
