Theory of twin-T RC-networks and their application to oscillators

The transmission properties of a twin-T RC-network are discussed in the first part of the paper. The condition is derived which the elements must satisfy in order that for one frequency (¿0) the network may have an infinitely great attenuation; next is discussed the condition which must be satisfied in order that, when two elements are altered in a particular manner, the output voltage of the network may be either in phase or in counterphase with the input voltage for the same frequency as the one for which the circuit had an infinitely great attenuation before the elements were altered. The circuit Q, to be defined for the network, is used to advantage, and forms the subject of a discussion. Finally, the slope of the phase-frequency characteristic for ¿= ¿0 is examined and this slope is compared with that of a parallel resonant LC circuit. The second part of the paper deals with the properties of an oscillator having one valve and containing such an RC-network. Special attention is paid to the freedom from distortion and to the amplitude and frequency stability. Finally the results of a measurement are compared with those obtained from a calculation.