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