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Stabilizing Circuitry

Author: Leonard Krugman

Figure 6-12 (A) illustrates one arrangement of a high-frequency base-controlled oscillator that incorporates the various stabilizing features discussed in the preceding paragraphs. C1 and C2 are phase compensating condensers. The base lead is connected to a tapped tank coil as a means of reducing the resonant impedance while maintaining a high Q tank. Bias stability is accomplished by using one common battery source. Notice also that positive emitter bias is supplied by the bypassed resistor RB. Figure 6-12 (B) illustrates an alternate method of providing a constant collector-to-emitter bias ratio by means of a common battery supply. The advantage of this circuit is its design simplicity, since it is basically a voltage divider network. The values of C1 and C2 are not critical; they complete the a-c circuit between the collector, base, and emitter leads, and bypass the battery and bias divider network.


Fig. 6-12. (A) Stabilized base-controlled high-frequency oscillator. (B) Alternate method of providing common bias supply.

Except for the inductance and capacitance elements of the resonant network, the values of the external components in negative-resistance oscillators are not critical The values of RE and Rc should be large enough to limit their respective currents to safe values, but not so large that they cause excessive degeneration. The value of the base resistance RB must be large enough to provide sufficient regeneration for sustained oscillation. Typical values for these parameters are: RE = 50 to 2,000 ohms; Rc = 2,000 to 10,000 ohms; RB = 10,000 to 20,000 ohms.

Last Update: 2010-11-17