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.
