## Answer 1.8

#### Because the mixer can be assumed to be a linear device, each component in the input waveform can be multiplied independently with each component in the carrier waveform. The result is the spectrum shown below. It is quite typical for local oscillator (carrier) sources to have a significant level of second or third order harmonic which would cause interference well outside the wanted modulation band. To overcome this problem, it is common to place a harmonic filter at the output of the mixer, or subsequent amplifier stages, to suppress this interference.