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Frequency Stability of Radio Circuits



    AT a meeting of the Students Section of the Institution of Electrical Engineers held on November 16, Mr. C. W. Eggleton read a paper on “The Frequency Stability of Tuned Circuits”. The author dealt with the conditions with which it is necessary to comply in the design of commercial radio receivers in order to secure a satisfactory degree of frequency stability in the various tuned circuits of the receiver. The majority of broadcasting receivers in use at the present time are of the supersonic heterodyne type using a local oscillator, and it is the frequency stability of this oscillator which usually determines the stability of the whole receiver, particularly when the required reception is within the short-wave band. Variations of the frequency of any tuned circuit are occasioned chiefly by the effect of temperature, and to a lesser extent by condensed moisture, on the electrical characteristics of inductance coils and condensers. In the paper, the author directed attention to the desirable properties of the materials used in the construction of these components, and to the importance of various features of design. An important point in connexion with the layout of the whole receiver is to ensure that the local oscillator and the main radio frequency circuits are kept as far away as possible from the power frequency components, which largely form the main source of heat generated in the receiver.

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