GB1305698A - - Google Patents

Abstract

1305698 Transistor radio receiving circuits MOTOROLA Inc 12 May 1971 [28 May 1970] 14499/71 Heading H3T A radio receiver includes a mixer circuit having first and second input terminals and an output terminal coupled to an I.F. utilization circuit, a local oscillator being coupled to the first input terminal of the circuit, while a radiofrequency amplifier circuit is connected in direct current series relation with the mixer circuit through an inductor connected to the second input terminal of the mixer circuit. Transistor 72 constitutes an R.F. amplifier in common emitter connection being fed from terminal 12a via tuned circuit 80, 81; its collector is connected via a signal-tuned circuit comprising inductor 76 and capacitor 79 to the emitter of transistor 73 which constitutes the mixer. In a first embodiment (Fig. 2, not shown) the R.F. transistor obtains a fixed base bias, and is neutralized by means of a capacitor connected between its base and the emitter of the mixer transistor. Transistor 87 constitutes the local oscillator, its emitter circuit comprising resistor 98 and being coupled to piezo-electric crystal 97 shunted by inductor 87; this is coupled by way of tuned circuit 90, 92, 93 to the collector of transistor 87. Local oscillations are injected on the base of transistor 73: the arrangement may employ continuously tunable circuits in order to cover a frequency band. The base bias for the oscillator 87 is derived via a D.C. amplifying transistor 78 from the emitter voltage of the mixer transistor 73. The collector circuit of mixer transistor 73 comprises a resistor 83 shunted by capacitor 84 and is D.C. coupled via diode 102 to the base of a first I.F. amplifying transistor 100; this is D.C. coupled to a second I.F. amplifying transistor 106, from the collector potential of which a base bias for the transistor 72 is derived over a line 113.