Improvements in or relating to radio telegraph diversity receiving systems

715,438. Radio receiving systems. STANDARD TELEPHONES & CABLES, Ltd. Aug. 26, 1952, No. 21422/52. Class 40 (5) In a space or frequency diversity receiving system for frequency-shift or amplitude modulated radio te'egraph signals D.C. signals different for " mark " and " space " are applied from amplitude demodulators 13 or frequency discriminators 7, corresponding to different signal paths or frequency channels equally to D.C. amplifier valves VI, V2 having common anode impedance R1 and a pair of gating valves V3, V4 having a common cathode impedance R2 are connected each in series with one of the valves V1, V2, and have a pair of control potentials representing the signal strengths in the paths or channels respectively applied to them so that one only of the gating valves V3, V4 is conducting at any time, due to the cathode coupling. Since the R.F. inputs to .the demodu'ators 13 and discriminators 7 are first passed through limiters 5, 6 and the valves V1 ... V4 form a bridge circuit the output signals from the impedance Rl are made constant in level before being applied, e.g. to a wave shaping flip-flop circuit and telegraph relay. Double pole switches 9, 10 permit changeover from A.M. to frequency shift operation. The signal strength voltages are derived, prior to the limiters, by tuned transformers T1, T2 and differentially connected diode detectors V5, V6 connected with the control grids of the gate valves V3, V4.