Improvements in or relating to telegraph systems

830,121. Code telegraphy. STANDARD TELEPHONES & CABLES Ltd. July 31, 1958, No. 24649/58. Addition to 808,461. Class 40 (3). [Also in Group XL (c)] In a radio diversity telegraph receiving arrangement in which a carrier wave bearing marking and spacing telegraph signals is received by a plurality of diversity antennas to any one of which a radio receiver can be connected, a " message - rate " discriminator measures the rate at which mark-space (or space-mark) transitions take place in the output from the receiver and controls means for disconnecting the receiver from one antenna and connecting it to another when the " messagerate " exceeds a predetermined value. In the diagrammatic arrangement, Fig. 1, with the contact a in the position shown, signals are passed from antenna 2 to a radio receiver 1, and then in parallel to a message-rate discriminator 5 and to a shaping amplifier 4 feeding a teleprinter 6. If the message rate exceeds the predetermined value, relay B operates, and over released contacts d1, d2 operates relay C which at contact c1 energizes relay A operating its contact a to connect the receiver 1 to the antenna 3. Relay D is short-circuited at the unoperated contacts d1 and d2, and if the reception on the antenna 3 is satisfactory relay B releases and at opened contact b removes the short circuit of relay D which operates in series with relay C. When the message-rate on antenna 3 exceeds the predetermined value, relay B again operates and over contact b short-circuits the relay C which releases and switches the receiver back to the antenna 2. If the reception on the antenna 2 is normal relay B releases and opens the circuit of relay D which releases and restores the circuit to the condition shown. The switches 8, 9 are used for setting up and adjusting the radio receiver 1, and with switch 9 operated the receiver can be connected at will to either antenna by manipulation of the switch 8. In the discriminator circuit, Fig. 2, with positive marking potential at the input 17, the valve 11 conducts and the valve 12 is cut off, whilst a spacing potential reverses the conditions of the valves. The output of valve 12 is fed to a differentiating capacitor 22 and the positive pulses on the mark transitions are by-passed via rectifier 30 to ground, whilst the negative pulses on the space transitions are passed via rectifier 23 to an integrating circuit comprising resistors 26, 27 and capacitors 28, 29, and having a time constant of about 0.2 sec. Afte