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