Transistor b.f.o.
Fig. 1 shows a transistor b.f.o. that can be used with any receiver having a 455 kc. i.f. It is basically a Colpitts oscillator and uses a 2N190 transistor. I built the unit in a b.f.o. can discarded from a 1.5 to 3 Mc ARC/5 receiver. The oscillator tank L1C1C2 is the b.f.o. coil assembly from the 1.5 to 3 Mc ARC/5 receiver. The oscillator is coupled to the receiver detector through the 5 pF capacitor. Since the unit requires only 12 volts at 60 µA, it makes a convenient b.f.o. for mobile operation. It can also be incorporated into the home receiver by using the voltage divider shown in Fig. 2. The divider is connected to the receiver B-plus line.
Fig. 1. Transistor b.f.o. The tuned circuit L1, C1, C2 is the b.f.o. assembly from a 1.5 to 3 Mc ARC/5 receiver.
Q1 2N190, CK768, 2N107.
Fig. 2. The voltage divider connects to a 250 to 300 volt source. Resistors are ½ watt.
Charles Hartley, K6GQL.