a first sub path configured to extract the second order intermodulation component from the path tuning {TAIL ~ signal} of {HEAD ~ the main path} 
a first sub path configured to extract the second order intermodulation component from the path tuning { TAIL ~ signal } of { HEAD ~ the main path }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD