The squarer output is applied to {HEAD ~ a summing amplifier}, which removes {TAIL ~ the multiplex frequency}, and which provides a dc signal which is applied to a comparator 
removes
The squarer output is applied to { HEAD ~ a summing amplifier } , which removes { TAIL ~ the multiplex frequency } , and which provides a dc signal which is applied to a comparator
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH