Patent GB-997267-A (GB)
Abstract: 997,267. Supervision of carrier frequency equipment. TELEFONAKTIEBOLAGET L. M. ERICSSON. May 29, 1963 [May 29, 1962], No. 21560/63. Heading H4R. In a carrier frequency transmission system in which separate signals are fed to a number of modulators each modulator being fed with a different carrier frequency and the outputs of the modulators are filtered and combined in a hybrid circuit to form a sub-sub-group, and a number of sub-sub-groups are similarly combined by modulators to form sub-groups, and a number of sub-groups are combined to form groups, and a number of groups are combined to form a super group which is then fed over a transmission link to the receiving equipment where a similar number of stages of demodulation are employed to obtain the original separate signals. Each group is provided at the transmitter with a group pilot signal which is used at the corresponding stage in the receiver, i.e. after the super group has been broken down to a number of groups, to control a regulating circuit which controls the amplitude of the group signal in accordance with the level of the group pilot signal. A number of measuring points are provided in the system, a first measuring point at the input to the receiving equipment at which the levels of the group pilot signals in the super group may be checked, a second measuring point after the first demodulator at the input to the regulating circuit, a third measuring point at the output of the regulating circuit, and, in the transmission side of the equipment, a fourth measuring point before each final modulator stage where the group pilot signal is added and a fifth measuring point at the transmitter output to enable the group pilot signals to be checked in the super group signal, the pilot signal levels at the first and second, or second and third, measuring points being checked by comparing the levels against each other and against a reference level. General arrangement.-Fig. 1 shows three stations A, B and C at which subscribers 23 are connected via exchanges 22 to carrier terminal equipment 21 the stations being connected by cables 20. At station B two carrier equipments 21 are provided one connected to station A and the other to station C. To provide for transmission from A to C, and vice versa, some of the channels in the two carrier equipments at station B are directly interconnected. Carrier terminal equipment, Fig. 2.-Each incoming speech signal in the band 300-3400 c.p.s. is applied via a low pass filter 24 to one modulator 25 of a group of 3 modulators each modulator of the group being fed with a different carrier frequency, e.g. 12, 16 and 20 kc ./s - After modulation one sideband of each signal is picked out in bandpass filter 26 and the three signals of the group are combined in a hybrid 27 to form a 3-group or sub-sub-group occupying the band 12-24 kc./s. Four 3-groups are combined by a second modulation stage comprising modulators 28, fed with carrier frequencies 84, 96, 108, and 120 kc./s., and bandpass filters 29 to form, at the output of hybrid 30, a " 12-group " or sub-group in the band 60-108 kc./s. To this sub-group is added a pilot signal at 84-08 kc./s. Each " 12 group " is then fed via, an amplifier 31 to a modulator 32 in one of a number of groups of five modulators the outputs of the five modulators of each group being filtered and combined in a hybrid 34 to form a " 60-group " in the band 312 to 552 kc./s. The " 60 groups " are supervised by pilot signals at 411-92 kc./s. added in hybrid 34. Fifteen of the " 60-groups " are then fed via a distribution frame 35, attenuators 36 and low pass filters 37 to modulators 38 where they are modulated with independent carrier signals and filtered in band pass filters 39 and fed to a hybrid device 40. One of the " 60-groups " is fed direct to the hybrid device 40 via link 2 and an attenuator so that the total of 16 "60-groups" form a " 960 group " or super group which is fed to the transmission line 20 via a hybrid 42. A " 960-group " pilot is added to the " 960- group " in hybrid 40. In the receiving side of the equipment the " 960-group " pilot is removed from the incoming signal in device 43. The " 960-group " is then fed via band pass filters 46, which select the individual " 60- groups," to modulators 47 and low pass filters 48 so that the " 60-groups " are extracted in their original band of 312-552 kc./s. The 60-groups are then passed via amplifiers 49 to a regulating circuit comprising variable attenuator 50, amplifier 51, hybrid circuit 52, and pilot receiver 53 which is connected to both the hybrid and the variable attenuator. The output from each regulating unit is then fed via the distribution frame 54 to a hybrid 55 and to a group of 5 demodulators 57 which extract the "12-groups." The "12-groups" are similarly fed through two further stages of demodulation to extract the original speech band signals. For " 60-groups " which are to be transmitted via further carrier equipment, e.g. those at station B in Fig. 1 which are passing between station A and C, the sets of carrier equipments are interconnected at distribution frames 35 and 54, i.e. terminals 15 and 16 on frame 54 would be connected to the corresponding terminals 15 and 16 on a distribution frame 35 in a second carrier equipment whilst the terminals 15 and 16 on the frame 54 in the second equipment would be connected to terminals 15 and 16 on frame 35 in the equipment shown in Fig. 2. Supervisory equipment. Fig. 5.-The carrier terminal equipment, part of which is shown within the dotted block at the top of Fig. 5, is provided with supervisory measuring points at 71 on the hybrid at the input of the receiving equipment, at 72 at the output of the first modulators in the receiver, at 73 on the output of the regulating devices 50-53, and in the transmitting side of the terminal equipment the level of the pilot added to the "60-groups" is monitored at point 74 and again in the output of the " 960-group " at point 75. The pilot level in the " 960-group " is monitored by feeding the " 960-group " signal from testpoint 71 (or 75 in the case of the transmitting side) through an amplifier, e.g. 76, to a modulator 77. The carrier feed to the modulator is from carrier frequency generating device 79 through relays 78 which cyclically connect the carrier frequencies of interest in order that each " 60-group " pilot signal is available in turn at the output of the pilot frequency (411.92 kc./s.) crystal filter 82. The relay 80 is provided to by-pass the modulator when the second " 60-group " signal is being monitored, this signal being in the band 312-552 kc./s. and not therefore requiring modulation to extract the 411À92 kc./s. pilot. The pilot signals from filter 82 are fed through amplifier 83, and rectifier 84 to a comparator unit 90. To one other input of the comparator 90 is applied the amplified and rectified pilot signal selected by crystal filter 86 which is cyclically connected to the outputs of the sixteen modulators 47 at the test points 72. The signals at the test points 71 and 72 are compared in unit 90 and the difference compared with a reference signal; if this difference shows an intolerable divergence, alarm device 92 operates and registration device 92 registers the place, the type, and the time of the fault. In a similar manner the outputs of the regulating devices at test points 73 are cyclically connected to pilot frequency crystal filter 95 and the level of the pilot signal here compared with the level at point 72, and divergences from the expected value operate warning and registering devices 101 and 102. In addition the absolute level of the pilot signal at point 73 is compared with a reference level in comparator 103 and divergences made to operate alarm and registration devices 105 and 106. In the transmitter side of the equipment the level of the pilot signal added to the " 60-group " is checked against a reference in unit 114 and the level of the pilot in the gransmitted " 960- group " is checked in unit 127. The pilot in the 960-group being extracted by a modulator arrangement similar to that used for the monitoring of the level at point 71 in the receiving equipment. The comparison and registration device within the lower dotted block in Fig. 5 is shown in detail in Fig. 6 in which the two signals to be compared at the outputs of amplifiers 87 and 96 are rectified and the two D.C. voltages fed each to two similar comparison circuits 99a and 99b. In each circuit the difference voltage is amplified in a transistor 131 and applied to two " long-tailed pair" circuits, e.g. transistors 135, 136 and transistors 132, 133. Transistor 135 has a reference potential, derived from Zener diode 138, applied to its base and transistor 137, having the difference voltage applied to its base, has a relay coil 137 in its collector circuit. If the difference voltage exceeds the reference potential on the base of transistor 135, transistor 136 conducts and relay 137 is operated to perform alarm and registration functions. Similarly if the difference voltage falls below the reference potential applied to the base of transistor 133, transistor 132 is cut off, 133 conducts and relay 134 operates. The circuit 99b operates in a similar fashion save that whereas the reference potentials in circuit 99a are set so that the relays 134 and 137 operate when the difference exceeds a predetermined first numerical value, the reference potentials in circuit 99b operate when the difference exceeds a second larger numerical value. The alarm circuits and register operate as follows, if e.g. relay 137 operates relay 144 is energized and makes contacts which lights alarm lamp 151 and energizes the starting relay 183 of the register device. In addition contacts on relay 144 operate relay 163, to register the type of fault, i.e. a small negative deviation of the difference voltage, and the one of relays 164-179 whic