GB622099A - Improvements in and relating to radio receiving apparatus - Google Patents

Abstract

622,099. Radio receiving sets; frequency modulation. BRITISH THOMSON-HOUSTON CO., Ltd. April 9, 1945, No. 8725. Convention date, April 12, 1944. [Class 40 (v)] in a frequency-modulation receiver, amplitude limiting is effected by a rectifier which passes only the positive half-cycles of the incoming wave to the grid of a further valve which limits these positive half-cycles by plate current saturation. The I.F. output is fed through a transformer 12 tuned to the mean I.F. and having the centre tap of its secondary winding 13 grounded. Positive half-cycles of the I.F. wave appearing across the upper half of the secondary 13 are fed through a rectifier 14 and appear across a load resistor 15. The lower end of the secondary winding 13 is coupled through a condenser 17 to the diode cathode. The condenser 17 has a capacitance equal to the inter-electrode capacitance 16 of the diode and serves to neutralize the effect thereof. The positive half-cycles appearing across the load resistor 15 are applied through a resistor 18 to the control grid 19 of a pentode 20 the anode circuit of which is coupled through a tuned transformer 31 to the discriminator 33. The control grid 19, being grounded through resistors 15, 18 is maintained at a slight negative or contact potential and the valve 20 operates in the region of plate current saturation to limit the positive half-cycles, Fig. 2 (not shown).