{HEAD ~ A source} of d.c control voltage is coupled to the input winding via a four terminal capacitor to control {TAIL ~ the impedance} of the secondary winding 
{ HEAD ~ A source } of d.c control voltage is coupled to the input winding via a four terminal capacitor to control { TAIL ~ the impedance } of the secondary winding
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH