Susceptance valves and reactance valves as phase modulators

Triode valves may be used in three different ways to give variable-impedance circuits. The most used form, usually known as a ¿reactance-valve circuit,¿ behaves much more as a variable ¿susceptance valve circuit.¿ Of the other two circuits, one is also a ¿susceptance-valve circuit,¿ while only the third is a ¿reactance-valve circuit¿ proper. All three kinds can be used successfully in phase modulator stages, with the feature that, for introducing phase variations of up to 45 deg, only one valve is necessary. Moreover, this may be realized with mutual-conductance variations of not more than 0·5 mA/V, from which follows both a high sensitivity and a good linearity.