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Fig. 14 Location of a faulty line repeater. If one direction is faulty in line repeater No. 4 only frequencies t s-f a are obtained at terminal B, whereas all frequencies f, — t e are obtained at terminal A tion over the route is eliminated by means of equalization. The equalization process is divded into coarse and fine equalization. The coarse equalization is carried out with fixed equalizers, one in the send direction for pre-equalization of the line and two in the receive direction for more accurate post-equalization. Each such device holds three correction networks. Theamount of equalization available in each direction of transmission is 6dB. The fine equalization is carried out by means of what is called an echo equalizer, which is based on the use of a delay line. The device contains 30 outlets, each of which has a variation range of ±3 dB. Adjustments are made with a potentiometer that is accessible at the front of the unit. A residual deviation curve can quickly be equalized with this equalizer. This equalizer can also be set up when the system is in service by using external test equipment and sending additional measuring frequencies over the system from the other terminal and measuring them. In addition to the equalization in the line terminal an equalization board can, if necessary, be included in each transmission direction in one of the non-regulating line repeaters. This board is designed as a fixed equalizer and the number required on a certain route will depend on how well the attenuation-frequency characteristic of the cable and the gain-frequency characteristic agree. To sum up it can be said that on short routes it is sufficient to have only fixed equalizers, or alternatively an echo equalizer, whereas on long routes both these aids are required and perhaps also some equalizer boards. The aim of the equalization is that the residual deviation curve for the route shall be within the limits of ±1 dB recommended byCCITT. Fault location Faulty line repeater It must be possible to locate a faulty line repeater rapidly and easily. For this purpose each repeater has been equipped with a simple crystal oscillator that generates an individual identification frequency, which is fed into both directions of transmission. The presence of the frequency can be checked with a selective level meter in the receiving terminal, and only the frequencies that emanate from the line repeaters after the faulty one will then be obtained, fig. 14. The fault location frequencies lie at intervals of 2 kHz in the band 3640- 4000 kHz. This makes it possible to supervise 180 line repeaters, which corresponds to a homogeneous section of 280 km. If the distant terminal station is unmanned the incoming fault location frequencies can be looped there and double modulated with the frequencies 7400 and 7220 kHz and then sent back. Half the available band is then used, i.e. frequencies that lie in the band 3820- 4000 kHz are shifted to 3640 -3820 kHz, whereby both transmission directions can be supervised from one and the same terminal. Another way of using the looping equipment is to send the modulated frequencies on in the same direction. A general equipment for supervision of the fault location frequencies has been developed for the 4, 12 and 60 MHz systems. Cable break The power feeding of the line repeaters is cut off immediately if the cable is broken, and thus the fault location Fig. 15 Location of a cable break. The amount of current fed out indicates where along the route the break has occurred
35 oscillators also cease operating. In order to find the break the output current from the remote power feeding unit is measured when a constant voltage of 600 V is supplied to the line from this unit. Each line repeater contains a highohmic resistor between the two transmission directions, through which a small amount of current can flow. The current measuring instrument in the remote power feeding unit has a special scale for measuring this current. When installing the system it is easy to calibrate and obtain the scale readings that correspond to the different line repeaters, fig. 15. Mechanical construction and installation As may be seen from fig. 16 there is space in one bay for two complete systems. Each system consists of a line terminating shelf stack, a terminal repeater, a remote power feeding unit and a mains rectifier. The bay also contains a speaker circuit shelf that is common for the two systems. The shelves are in the M4 construction practice and the width of the bay is 600 mm. The line repeater is of the same mechanical design as in the other systems in the new generation. It consists of a small die-cast aluminium box with the dimensions 130x210x310 mm including the handle 4 . The line repeaters are installed in a waterproof cylindrical steel housing, which is buried in the ground or placed in a manhole. One of the types supplied by LM Ericsson holds three systems and this housing has a height of 750 mm and a diameter of 510 mm. When the line repeater is to be insulated from earth it is provided with an external case, fig. 17. This case is also used to absorb strong vibrations, which can occur when the cable is laid along motorways or railways. The line repeaters are easy to install if they are correctly equipped beforehand. This means that they are provided with — suitable gain — a crystal for the fault location — if necessary a line building-out network. Out in the field it is then only necessary Fig. 16 60 MHz terminal bay The equipment for a fully equipped system is shown TR Terminal repeater LT Line termination PFU Remote power feeding unit SCS Speaker circuit shelf FLS Fault location shelf MR Mains rectifier opt Optional Fig. 17 The cover for the line repeater, intended to Insulate it from earth and protect it from vibrations
Page 1: ERICSSON REVIEW 1 1978 OPERATIONAL
Page 5 and 6: ERICSSON REVIEW NUMBER 1 • 1978
Page 7 and 8: 3 STEN RIMBLEUS Stockholm Telecommu
Page 9 and 10: Fig. 4 (left) The operation and mai
Page 11 and 12: Types of faults, measures and subsc
Page 13 and 14: 9 ABDULLAH AL-SABEJ Chief Engineer
Page 15 and 16: Stored Program Controlled PABX, ASB
Page 17 and 18: 13 When the receiver is lifted the
Page 19 and 20: 15 five such matrices permit connec
Page 21 and 22: 17 Fig. 8 Printed board assembly fo
Page 23 and 24: Technical data Capacity Number of e
Page 25 and 26: 21 HENNING ANDERSEN VILLYK. PEDERSE
Page 27 and 28: 23 signalling was to be carried out
Page 29 and 30: 25 Fig. 10 Simplified block diagram
Page 31 and 32: Fig. 12 The principle for common tr
Page 33 and 34: PER-ALRIK HALLBERG THORWALD LUNDMAR
Page 35 and 36: 31 Fig. 9 Regulation range for the
Page 37: Fig. 12 Power feeding of the line r
Page 41 and 42: Technical data Electrical data Cabl
Page 43 and 44: 39 CHRISTOPHER LORENZ Financial Tim
Page 45 and 46: The Ericsson Group With associated

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