{HEAD ~ The filtered signal} is squared to provide {TAIL ~ a squared signal} alternating at the frequency fm between values related to sin2 fx and cos2 fx 
is squared to provide
{ HEAD ~ The filtered signal } is squared to provide { TAIL ~ a squared signal } alternating at the frequency fm between values related to sin2 fx and cos2 fx
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH