Spectrum analysis can be used to create a profile of {HEAD ~ an active signal source} that can be analyzed to identify {TAIL ~ the type} of source producing the signal 
analyzed to identify
Spectrum analysis can be used to create a profile of { HEAD ~ an active signal source } that can be analyzed to identify { TAIL ~ the type } of source producing the signal
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH