. The Bell System technical journal . generally undesirable. Elements which give approximately the characteristics called for in are shown in Fig. 25. The peak of loss at one megacycle is contributedby the series resonant trap. The rest of the behavior is due to the nicondenser in combination with the associated resistors. 20 BELL SYSTEM TECHNICAL JOURNAL XII. Auxiliary Control of Thermally Limited Oscillators In the Meacham and certain other oscillator circuits a thermistor isassociated with reactive elements in a bridge circuit which functions as bothlimiter and filter. In these c
. The Bell System technical journal . generally undesirable. Elements which give approximately the characteristics called for in are shown in Fig. 25. The peak of loss at one megacycle is contributedby the series resonant trap. The rest of the behavior is due to the nicondenser in combination with the associated resistors. 20 BELL SYSTEM TECHNICAL JOURNAL XII. Auxiliary Control of Thermally Limited Oscillators In the Meacham and certain other oscillator circuits a thermistor isassociated with reactive elements in a bridge circuit which functions as bothlimiter and filter. In these circuits a large increase in the frequency stabihtyis observed. This may sometimes be conveniently expressed as a magnifica-tion of the effective Q of the filter. The advantages of great frequency stabihty and good amphtude stabilityof these systems are accompanied by an undesirable tendency towardintermittent operation. The thermal constants of the thermistor are notreadily adjustable. Moreover adjustment of the reactances to secure. Fig. 26—Meacham circuit with auxiliary control. suitable envelope stability is likely to impair the frequency or amplitudestability for which the circuit is chosen. This dilemma may be resolved by the addition of an auxiliary networkwhich does not affect the envelope transmission to very low frequencies butdoes modify the behavior at higher frequencies in such a way as to promotethe stability of the system. A simple circuit illustrating the principle appears in Fig. 26. It will benoticed that the circuit is so arranged that the average bias applied to thetube is only that due to the cathode resistor. The steady voltage developedacross Ci by the rectifier is unable to affect the bias because of the blockingcondenser C2. Accordingly the rectifier circuit does not affect the normaloperating condition, which is characterized by a bridge loss equal to theamplifier gain. The added elements come into play only if there is a tend-ency toward self-modulat
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