a variable attenuator connected to {HEAD ~ the self test amplifier} via a mixer, and the microprocessor to generate a testing signal based on input from the self test amplifier and {TAIL ~ the microprocessor} 
a variable attenuator connected to { HEAD ~ the self test amplifier } via a mixer , and the microprocessor to generate a testing signal based on input from the self test amplifier and { TAIL ~ the microprocessor }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL