Clarifications on Mixer Math

The first comment referred to the statement that mixers are nonlinear circuits, and is from Alan Victor. “Saw you mixer tutorial and one point that grabbed my attention is the ‘Mixers are nonlinear circuits’. Whoa! Mixing is quite real in linear systems and the linear mixing function is readily seen by multiplication of linear transconductance with a time varying signal voltage. Your cosine product equation in the second column of the page 34 shows this concept. See also Steve Maas’ text on the same, “An Improved Linear Mixer: The FET Resistive Mixer.”