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