The Autodyne Converter Circuit Using A Na As A Mixer

signal from the collector to the emitter causing oscillation. Capacitor G tunes the oscillator circuit to a frequency 455 kc. higher than that of the incoming signal. The local oscillator signal is inductively coupled into the emitter circuit of the transistor. The incoming signal is resonated in T2 and coupled via a low impedance winding to the base circuit. Notice that the base is biased by a voltage divider circuit much the same as is used in audio frequency operation. The two signals are mixed in this stage and the desired beat frequency of 455 kc. is selected by i-f transformer Ta and passed to the next stage. Collector currents of 0.6 ma. to 0.8 ma. are common, and the local oscillator injection voltage at the emitter is in the range of 0.15 to 0.25 volts, r.m.s.

A complete receiver "front end" capable of operation up to 23 Mc. is shown in figure 21. The RCA 2N247 drift transistor is used for the r-f amplifier (TR1), mixer (TR2), and high frequency oscillator (TR3). The 2N247 incorporates an interlead shield, cutting the interlead capacitance to .003 /¿/uid. If proper shielding is employed between the tuned circuits of the r-f stage, no neutralization of the stage is required. The complete assembly obtains power from a 9-volt transistor battery. Note that input and output circuits of the transistors are tapped at low impedance points on the r-f coils to achieve proper impedance match.

Figure 21 RF AMPLIFIER, MIXER, AND OSCILLATOR

STAGES FOR TRANSISTORIZED HIGH FREQUENCY RECEIVER. THE RCA 2N247 DRIFT TRANSISTOR IS CAPABLE OF EFFICIENT OPERATION UP TO 23 Mc.

Figure 21 RF AMPLIFIER, MIXER, AND OSCILLATOR

STAGES FOR TRANSISTORIZED HIGH FREQUENCY RECEIVER. THE RCA 2N247 DRIFT TRANSISTOR IS CAPABLE OF EFFICIENT OPERATION UP TO 23 Mc.

Transistor Autodyne

Transistor Sufficient coupling of the proper Oscillators phase between input and output circuits of the transistor will permit oscillation up to and slightly above the alpha cutoff frequency. Various forms of transistor oscillators are shown in figure 22. A simple grounded emitter Hartley oscillator having positive feedback between the base and the collector (22A) is compared to a grounded base Hartley oscillator (22B). In each case the resonant tank circuit is common to the input and output circuits of the transistor. Self-bias of the transistor is employed in both these circuits A more sophisticated oscillator employing a 2N247 transistor and utilizing a voltage divider-type bias system (figure 22C) is capable of operation up to 50 Mc. or so. The tuned circuit is placed in the collector, with a small emitter-collector capacitor providing feedback to the emitter electrode.

A P-N-P and an N-P-N transistor may be combined to form a complementary Hartley oscillator of high stability (figure 23)- The collector of the P-N-P transistor is directly coupled to the base of the N-P-N transistor, and the emitter of the N-P-N transistor furnishes the correct phase reversal to sustain oscillation. Heavy feedback is maintained between the emitter of the P-N-P transistor and the collector of N-P-N transistor. The degree of feedback is controlled by Ri. The emitter resistor of the second transistor is placed at the

Npn Pnp Oszillator

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