GB579565A - Improvements relating to demodulating apparatus for pulse signalling systems - Google Patents

Abstract

579,565. Pulse modulation. COSSOR, Ltd., A. C., and BELL, D. A. Sept. 17, 1943, No. 15305. [Class 40 (v)] A demodulator, for signals conveyed by a series of identical pulses modulated as to their phase or frequency, comprises means for mixing the received pulses with a saw-tooth oscillation of the same mean frequency thereby producing an output which varies with the phase relationship of the components, and represents the signal or modulation. The frequency or phase of the saw-tooth oscillation may vary with that of the incoming pulses and to a nearly equal degree. As shown, the pulses are derived by rectification of a received carrier in the valve 3 and are applied from the anode of that valve to the mid-point of the secondary coil of a transformer 27, the primary of which is fed from a saw-tooth generator 35 of the blocking oscillator type. The mixed oscillations pass through balanced diode rectifiers 25, 26 to load resistances 28, 29 and an output transformer 32 feeding a signal amplifier 33 and reproducer 34. The frequency or phase of the saw-tooth oscillator may be made to follow that of the received pulses by a connection across the load resistances 28, 29 into the grid circuit of the valve 35., Condensers 30, 31 byepass the pulse frequency. In a modification, Fig. 3 (not shown), the received pulses are broadened by a condenser-resistance combination in the anode circuit of the valve 3 ; and the mixing of the pulses with the saw-tooth oscillation is effected by applying them to separate control grids of a mixer valve of the double-control type.