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