Mathematically speaking, FM & PM are almost identical twins. The only difference is that one corresponds to a modulation pattern which is the differential of that produced by the other. The ‘good news’ is that this means we can mix FM & PM arguments and most of our conclusions about one apply to the other. In FM, the frequency of the carrier signal increases and decreases to represent the change in voltage of the base signal. AM usually broadcasts in mono which makes it sufficient for talk radio, whereas, FM can transmit in stereo which makes it ideal for music. FM usually has a better signal quality than AM, but a far reduced range. FRIENDS OF PM The Friends of PM allows you to directly help impact, amplify, and revitalize the discourse and actions of radical writers, filmmakers, and artists. It provides us with a stable foundation from which we can build upon our early successes and provides a much-needed subsidy for the materials that can’t necessarily pay their own way. Before introducing am and pm, children should be introduced to the two important terms - noon (midday) and midnight. 12 at the day time is called noon and 12 at the night is called midnight. (There is a common mistake which many people make and that is calling 12 p.m. and 12 a.m. For FM, integration is a linear operation we use the results from PM to see that the instantaneous frequency and phase are linear but the actual modulated signal is not.