Measurement of the dynamic amplitude-phase characteristics of a TWT

Zen'kovich (1974, 1975) has developed a method for measuring the coefficient of conversion of the amplitude modulation of a TWT into frequency (phase) modulation. The method is based on the separation of the FM of interest which arises in the TWT from the FM arising in the AM-oscillation source and in the FM receiver; the method includes compensation of the frequency (phase) modulation of the AM-oscillation source. In this case, however, the resolving power of the measurement (the minimum measurable magnitude) is limited by the coefficient of conversion of AM to FM in the receiver of FM oscillations, and in certain cases the resolving power is insufficient. In the paper, a method is proposed to eliminate this insufficiency: compensation of FM (or phase modulation) arising due to AM in the FM-oscillation receiver is employed. This compensation is effected by introducing a modulating LF voltage with its harmonics (with appropriate amplitude and phase) into the output circuit of the receiver.