GB562702A - Improvements in or relating to receivers for receiving angular velocity-modulated carrier wave signals - Google Patents

Abstract

562,702. Frequency and phase modulation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Jan. 8, 1943, No. 360. Convention date, Oct. 25, 1941. [Class 40 (v)] In a receiver for carrier waves modulated in frequency or phase by a desired signal and in amplitude by an undesired signal or noise, the residual A.M. signal present in the output of the frequency demodulator is reduced or eliminated by combining that output in a modulating element with the output of an amplitude detector. As shown in Fig. 2, the modulated carrier is applied to a balanced frequency discriminator of the off-tune type and each rectifier has its load resistance in two sections R1, R2, R3, R4. The voltage taken off across resistances R2, R4 in the normal way by the potentiometer 6 comprises the F.M. signal, and is also found to contain the undesired A.M. signal as an amplitude modulation of the desired F.M. signal, as in Specification 562,553. On the other hand, the voltage across the resistances R1, R4 taken off by the potentiometer 5 represents the A.M. signal only. The latter is applied to the inner grid 4<1> of a mixing or modulating valve 4 so as to modulate or vary in inverse sense the signal applied from the potentiometer 6 to an outer grid 4<11>. The resultant signal in the anode circuit is taken off by a potentiometer 8 and applied to a further amplifier 7. The signal applied to the grid 41 is present in this resultant and is removed by connecting that grid to the grid 7<11> of a further valve which has its anode connected to the anode of the valve 7, the final output across resistance 9 comprising the F.M. signal with the A.M. signal substantially eliminated. The process of removing the A.M. signal may be repeated, Fig. 3 (not shown). The stage represented by the valve 7 may be omitted by providing sliders on the resistances R1, R4 so as to apply selected fractions of the available voltages to the potentiometers 5, 6, Fig. 4 (not shown). In Fig. 5, the voltage on potentiometer 6 is applied to a grid of a valve 4 to modulate a carrier wave supplied by an oscillator 33, the modulated output being applied to a valve 25 where it is inversely modulated by the voltage on the potentiometer 5. The carrier output is rectified at 26, giving the F.M. signal substantially free from residual A.M. signal. The Specification also describes a phase modulation receiver, Fig. 6 (not shown), in which the output from a phase demodulator is combined with the output of an amplitude demodulator in valves arranged similarly to the valves 4, 7 of Fig. 2. Specifications 482,740, 526,259 and 545,577 are referred to.