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Consumer Electronics by S. P. Bali

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PRACTICAL AM TUNER CIRCUIT

Fig. 28.6 illustrates the circuit of a broadband a.m. broadcast band tuner. The a.m. r.f. amplifier transistor, Q201, is a 2N1732 in a common-emitter circuit. The ferrite-rod antenna shown at the extreme left on the schematic is tuned by one section of the three gang a.m. tuning capacitor (C118D). A common trouble with a.m. tuners is a broken antenna loopstick. Should the ferrite rod become cracked, the receiver will tend to exhibit low a.m. sensitivity.

The r.f. signal from the antenna is coupled to the base circuit by the few-turn secondary winding (marked H in schematic). This provides for an impedance match to the r.f. amplifier base circuit. Automatic gain control is applied to the base by means of resistor R201. ...

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