Shifting the frequency of a received signal

This application concerns a converter for shifting a frequency of a received input signal (Sig1, Sig 2) to form an output signal at a predetermined intermediate frequency band. The converter includes a mixer (20A, 20B, Fig. 2) driven by a local oscillator (L01, Fig. 2). The converter further comprises control circuitry configured to select the local oscillator to be higher than a frequency of the received input signal (high-side injection, LOh) or lower than a frequency of the received signal (low-side injection, LOl). High-side injection or low-side injection is selected in dependence upon current conditions. The current conditions may include: i) the strength of an image frequency band, IM_ob1, IM_ib1, IM_ib2, IM_ob2; ii) a quality of a signal output from the converter; or iii) the proximity an input signal to the edge of the Ku band used to carry the input signal. In the embodiment of Figure 4, all three of these current conditions are considered together. Preferably a further mixer (22, fig. 2) and a further local oscillator (L02, fig. 2) are provided for down-conversion from IF to baseband. In this case, the current conditions may involve considering the strength of harmonics of the baseband signal.