sources 7 and 8 respectively the tetrode power tubes 5 and 6 are linked by a tuned circuit formed by variable capacitors 9 and 10 and inductor 11 this tuned circuit is used to impedance match the tetrode power tubes 5 and 6 the tetrode power tube 6 is linked to a remote antenna 12 by a matched transmission line made up of a plurality of inductances 13 and variable capacitances 14 if efficiency of a transmission is defined as the ratio of output power to input power it is possible to measure the efficiency of a radio transmitter directly by comparing the cathode current in the tetrodes with the forward rf voltage into the load if a curve of component value the component value being for example inductance if the component is a variable inductor such as inductor 3 in fig1 or capacitance if the component is a variable capacitor such as capacitors 9 10 and 14 in fig1 is plotted against transmitter efficiency for a reactive component in the transmitter a curve that is highly symmetrical about its maximum for component values close to the maximum is obtained in order to tune the transmitter to maximum efficiency the values of the variable components 3 9 10 and 14 will need to be adjusted the way in which this is done will be.