Some Properties of Grid Leak Power Detection

It is shown theoretically that grid leak power detection can be obtained without undue distortion provided the grid condenser reactance X to the modulation frequency, and the grid leak resistance R are related to the degree of modulation m in such a way that X/ R . m/ V1 -iM2. The load limit of the grid leak power detector is the point where plate rectification becomes appreciable, i. e., when the straight line part of the plate characteristic is exceeded. Theory is developed which indicates that the maximum carrier voltage a grid leak power detector will handle is slightly less than one-half the input voltage that the tube will take as a properly adjusted amplifier operating at the same plate voltage; and that the maximum undistorted audio-frequency output voltage of the detector is in the neighborhood of one-third the output voltage developed by the corresponding amplifier. The equivalent input resistance of a grid leak power detector is proved to be greater than one-half the grid leak resistance. Experimental results are given which verify the theoretically determined point at which distortion becomes excessive. These results indicate that the grid leak power detector is more sensitive than the C bias power detector, and will ordinarily give at least as much undistorted output when operated at the same plate voltage.