Autogenerator

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Autogenerator - the single transistor (in the older devices - vacuum tube) generator that was commonly used as the local oscillator in the superheterodyne radio receivers.

The autogenerator frequency is determined by the oscillatory LC loop with the variable capacitor (hence the frequency of the autogenerator can be tuned).

[edit] The work of transistor

The typical autogenerator consumes 1.5 - 4 mA of current (I). During the normal work of transistor, the voltage between the ground and emitter, U_e, is equal to about 0.2 of the voltage of the power source (E_n), and the voltage between the ground and collector is equal to about 0.8 of the power source. This mode is determined by resistors R1 - R4 that are also responsible for the thermal stability of the generator.

The oscillatory loop, determining the frequency of the oscillation, is formed by the L_k and C₄.

[edit] The reasons of choosing between designs

Autogenerators, producing relatively low frequencies (below 2-4 MHz) usually use additional windings on the oscillatory LC loop to provide the positive feedback, required for the generation. The oscillatory loop in this case also works like transformer or autotransformer. For the higher frequencies the computed number of windings is too small (surely cannot be less than one), and it is easier to create the positive feedback using the capacitory divider.

[edit] Reference

Vasilijevich I, Budennyj A. (1964) Calculation of the autogenerator with transistors (in Russian). Radio, 7, p. 40 - 42 (sovietpd).