GB612585A - Improvements in receivers for angle-modulated carrier waves - Google Patents

Abstract

612,585. Frequency modulation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 29, 1946, No. 16280. Convention date, May 29, 1945. [Class 40 (v)] Relates to receivers for angle-modulated waves of the kind described in Specification 562,993 in which the incoming wave, or an intermediate frequency wave derived therefrom, is applied as a synchronizing voltage to lock in a local oscillator tuned to a subharmonic frequency; and consists in providing a resonant network coupled with, and tuned to the same frequency as, the oscillator tank circuit, thereby increasing the lock-in range. As shown in Fig. 2, the oscillator is a pentagrid valve 1 with its tuned anode circuit 5 back-coupled through an untuned grid circuit 5<1> to an intermediate grid 6. The incoming wave after conversion to an intermediate frequency is applied through coupled resonant circuits 14, 15 to the inner control grid 2 of the valve. The anode circuit 5 is tuned to a subharmonic frequency, say one-fifth of that applied to the grid 2, and is damped by a variable resistor R4. Magnetically-coupled to the circuit 5 is a damped, tuned circuit 5<11> resonant at the same frequency, the coupling being adjustable, but preferably closer than the critical value. The three coupled coils are wound in sections and are mounted on a tubular former. Coils L1, L2 are close coupled, and coil L3 is spaced therefrom and axially adjustable. Comminuted iron cores are adjustably mounted within the former for tuning, Fig. 3 (not shown). The discriminator shown in Fig. 2 is substantially the same as that described in Specification 562,993, but may be replaced by other types, e.g. that described in Specification 489,094. In Fig. 7, the discriminator comprises a damped, tuned circuit 40 parallel-resonant at or near the upper end of the frequency range, and in conjunction with the condenser 36 affording series resonance at the lower end of that range. A diode 17 shunted by a load resistor R6 is connected between earth and the input from the local oscillator. The audio output is taken across the resistor R6 and de-emphasis of the higher notes may be effected by resistor R8 and condenser 29. Specification 609,496 and U.S.A. Specification 2,341,240 also are referred to.