Patent ID: 7697632

Claim:
A low Intermediate Frequency radio receiver comprising: antenna means for receiving a slot-based radio signal at a carrier frequency and comprising successive frames each comprising a set of reception time slots; input means responsive to a signal from said antenna means for producing an input signal; local oscillator means for producing local oscillator signal In-phase and Quadrature components having a local oscillator frequency; mixer means for mixing said input signal with said local oscillator signal In-phase and Quadrature components and producing Intermediate Frequency signal In-phase and Quadrature components; filter means responsive to said Intermediate Frequency signal In-phase and Quadrature components for selectively passing frequencies within a low Intermediate Frequency range and rejecting frequencies outside said low Intermediate Frequency range so as to produce filtered signal In-phase and Quadrature components; further local oscillator means for producing further local oscillator signal In-phase and Quadrature components having a further local oscillator frequency; further mixer means including In-phase and Quadrature channels for mixing said filtered signal In-phrase and Quadrature components with said further local oscillator signal In-phrase and Quadrature components and producing baseband signal In-phase and Quadrature components; and baseband filter means responsive to said baseband signal In-phase and Quadrature components for selectively passing frequencies within a baseband frequency range and rejecting frequencies outside said baseband range; wherein said local oscillator means includes frequency alternation means for causing said local oscillator frequency to alternate a plurality of times during said reception time slots of each of said frames between first and second values one of which is greater and the other smaller than said carrier frequency; and wherein said further local oscillator means includes phase alternation means for applying alternating phase shifts to said further local oscillator signal In-phrase and Quadrature components in synchronism with said local oscillator frequency alternations.