The increasing number of the power levels is achieved by using electrical elements, such as {HEAD ~ resistors}, transformers and {TAIL ~ others} 
The increasing number of the power levels is achieved by using electrical elements , such as { HEAD ~ resistors } , transformers and { TAIL ~ others }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL