Patent GB-1158810-A (GB)
Title: Pulse transmission system
IPC: H04B17/40
Filed: 1967-04-27
Abstract: 1,158,810. Radio-frequency systems; data transmission systems. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 22 April, 1967 [30 April, 1966], No. 19471/67. Addition to 1,158,809. Headings H4L and H4P. A pulse signal transmission system of the kind described in the parent Specification is characterized by the transmitting station comprising an adjustable test pattern generator, and by those intermediate repeater stations which include code converters being connected on their output sides through test pattern detectors to a return circuit to the transmitting station. A test pattern detector at a repeater station will only supply a signal to the return circuit when a characteristic test pattern is applied during testing. As described, a transmitting station 2, Fig. 1, serving a receiving station 8 via three repeater stations 5, 6, 7, comprises a signal generator 3, an inverse code converter 24, an adjusting switch 49, and an output amplifier 4. The inverse code converter 24 comprises sections 25, 26, 27 in series each made up of a modulo 2 adder (or non-equivalence element) having one direct input and one input from its output delayed by one clock pulse period T by devices 31, 32, 33. The fixed contacts of the switch 49 are connected to the inverse code converter 24 so that either one or two or three sections may be in circuit during testing, according to which repeater station is concerned. The signal generator 3, the tapped inverse code converter 24, and the switch 49 function as an adjustable test pattern generator 34. Each repeater station 5, 6, 7 comprises an equalizing network 10, a pulse regenerator 12, a code converter 21 and a pulse amplifier 11. The pulse regenerator 12 comprises a gating device 15 which is connected through a bistable trigger 17 to the output of the equalizing network 10, and is controlled by a clock pulse generator 19, which is likewise connected to the said output. The converter 21 comprises a modulo 2 adder (or non-equivalence element) 22 with one input directly from the output of the pulse regenerator 12 and the other input from the said output after delay by one clock pulse period T at 23. The output of the code converter 21 is supplied to a test pattern detector 36 comprising a selective amplifier 40 tuned to the fundamental frequency f 0  of the characteristic test pattern, a rectifier 43, which is biased to provide a threshold against false operation, a smoothing filter 44, and an amplifier 45. Output from the amplifier 45 is connected to a return circuit 35, supplying direct current indicator 39 at the transmitting station 2. At the receiving station 8, there is an equalizing network 13, a pulse regenerator 14, and a reproduction device 9. When testing, for example repeater station 5, the switch 49 is placed so that section 25 only of the inverse code converter 24 is in circuit, and the characteristic test pattern is applied by the signal generator 3. This may consist of repetitions of four pulses "on" followed by four pulses "off" so that the period is 8T, and the fundamental frequency f 0  is 1/8T. This pattern is inverse coded by the section 25 of the inverse code converter 24 and is restored to its original form by the code converter 21. The test pattern detector 36 of the repeater station 5 consequently produces an output to the return circuit 35, and the indicator 39 is operated. Subsequent codings at the repeater stations 6, prevent their test pattern detectors 37, 38 being operated (Fig. 2, not shown). In a similar way, the repeater stations 6, 7 may be tested, by appropriately setting the switch 49. In another embodiment, test pattern detectors 50, 51, 52, Fig. 3, at repeater stations 5, 6, 7 each comprise a gating device 53 into which clock pulses are fed from the pulse regenerator 12, said gating device being controlled by output voltage from the code converter 21. The output of the gating device 53 is taken to an integrating device 54, which is shunted by a diode 55, and which is connected through a threshold device 56 and an amplifier 57 to the return circuit 35. In this case, the characteristic test pattern is a continuous signal (Fig. 4, not shown), which is recovered at the repeater station under test, but which appears as pulses or as no signal at the others. The gate 53 at the repeater station under test is opened, the threshold device 56 is overcome, and a signal is sent over the return circuit 35 to the indicator 39. The diode 55 at the station under test is biased to be non-conductive by the steady output voltage from the code converter 21, but at a station not selected for test where pulses are being received, discharges the integrating device during "off" periods, so that it does not build up sufficient voltage to overcome the threshold device.