An apparatus comprising: means for modulating a first carrier signal with a first input signal to provide a first output signal; means for modulating a second carrier signal with a second input signal to provide a second output signal, wherein the first and second input signals are derived based on a first modulating signal, A I (t); means for modulating a third carrier signal with a third input signal to provide a third output signal; means for modulating a fourth carrier signal with a fourth input signal to provide a fourth output signal, wherein the third and fourth input signals are derived based on a second modulating signal, A Q (t); means for combining the first, second, third, and fourth output signals to provide a modulated signal; wherein: each of the means for modulating (230a,b,c,d) comprises means for amplitude modulating the respective carrier signal; and the first and third carrier signals have a phase shift of 90 degrees; and characterised in that: the first, second, third and fourth input signals have an offset value, K, and the first and fourth input signals are obtained by adding the offset value K to the first and second modulating signals respectively and the second and third input signals are obtained by adding the offset value to the inverted first and second modulating signals respectively and the second and fourth carrier signals have an inverted phase with respect to that of the first and third carrier signals respectively; and the modulated signal comprises an inphase component formed by the first modulating signal and a quadrature component formed by the second modulating signal. means for modulating a first carrier signal with a first input signal to provide a first output signal; means for modulating a second carrier signal with a second input signal to provide a second output signal, wherein the first and second input signals are derived based on a first modulating signal, A I (t); means for modulating a third carrier signal with a third input signal to provide a third output signal; means for modulating a fourth carrier signal with a fourth input signal to provide a fourth output signal, wherein the third and fourth input signals are derived based on a second modulating signal, A Q (t); means for combining the first, second, third, and fourth output signals to provide a modulated signal; wherein: each of the means for modulating (230a,b,c,d) comprises means for amplitude modulating the respective carrier signal; and the first and third carrier signals have a phase shift of 90 degrees; and characterised in that: the first, second, third and fourth input signals have an offset value, K, and the first and fourth input signals are obtained by adding the offset value K to the first and second modulating signals respectively and the second and third input signals are obtained by adding the offset value to the inverted first and second modulating signals respectively and the second and fourth carrier signals have an inverted phase with respect to that of the first and third carrier signals respectively; and the modulated signal comprises an inphase component formed by the first modulating signal and a quadrature component formed by the second modulating signal. each of the means for modulating (230a,b,c,d) comprises means for amplitude modulating the respective carrier signal; and the first and third carrier signals have a phase shift of 90 degrees; and characterised in that: the first, second, third and fourth input signals have an offset value, K, and the first and fourth input signals are obtained by adding the offset value K to the first and second modulating signals respectively and the second and third input signals are obtained by adding the offset value to the inverted first and second modulating signals respectively and the second and fourth carrier signals have an inverted phase with respect to that of the first and third carrier signals respectively; and the modulated signal comprises an inphase component formed by the first modulating signal and a quadrature component formed by the second modulating signal. the first, second, third and fourth input signals have an offset value, K, and the first and fourth input signals are obtained by adding the offset value K to the first and second modulating signals respectively and the second and third input signals are obtained by adding the offset value to the inverted first and second modulating signals respectively and the second and fourth carrier signals have an inverted phase with respect to that of the first and third carrier signals respectively; and the modulated signal comprises an inphase component formed by the first modulating signal and a quadrature component formed by the second modulating signal.