Patent GB-830121-A (GB)
Title: Improvements in or relating to telegraph systems
Inventor: HOLLAND JOHN DOUGLAS
IPC: H04L1/06
Filed: 1958-07-31
Abstract: 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. After a number of negative pulses determined by the setting of a potentiometer 33, a negative voltage passed via rectifier 32 is sufficient to cut off the normally conducting valve 31, so that the associated valve 38 conducts and operates the relay B. The shaping amplifier may contain two interconnected valves, similar to 11, 12, Fig. 2, and the triggering levels may be arranged to be close to the normal output voltages of the receiver 1 for mark and space respectively, whilst the valves 11, 12 of the discriminator are arranged to be triggered by relatively small positive and negative outputs from the receiver 1. If the reception on both antennas 2, 3 is much disturbed, the circuit, Fig. 1, may incorporate an auxiliary discriminator which, as described in the parent Specification, controls relays to disconnect the teleprinter 6 until the reception on one of the antennas is such as to provide a message-rate less than the prescribed value.