Colour Display System SEMIGRAF 240 - The history of Ericsson

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Fig. 10 Branching for direct termination Fig. 11 Branching for remote termination Telephony channels Fig. 12 Remotely fed branching terminal Main traffic Branched traffic Fig. 13 Remote power feeding unit with instruments for output voltage and current. The press buttons on the right are used when locating a cable break A fault in a repeater is located with the aid of an oscillator built into the repeater. Each oscillator is tuned to a fault location frequency which is individual for each repeater station. The fault location frequencies lie in the band 4800- 5000 kHz at intervals of 2 kHz , and they can be measured in the receiving terminal using an ordinary selective instrument. Branching An important requirement for the category of line systems to which ZAX-ZAC 120 T and 480 T belong is that it must be possible to branch off the wanted number of channels at arbitrary places along the line, in an easy and economical way. This facility has already been exploited in many cases where the first generation of ZAX 120 T has been installed. The frequency plans that apply for the 120 and 480-channel systems, where the modulation frequency for the high line band is always accessible on the line, makes it easy to arrange both stop and leak branching. Stop branching in two-wire systems can only be arranged at a four-wire point, which means that the line group bands in both directions are terminated in the ordinary way by translation to the basic frequency band. In such a station it is also possible to arrange equalization and remote power feeding and it is also easy to carry out frequency frogging, which is advantageous as regards noise in the case of very long lines. Stop branching 5 , which is also utilized on large line systems, is well known and will not be discussed in detail here. Leak branching can be arranged on two-wire systems without the necessity of terminating the line group band in the main through path. The main advantages of this method are that it requires very little extra equipment and that local arrangements and power losses do not affect the main through-going traffic. The disadvantage of leak branching is that the frequency band that has been branched off cannot be used for new traffic after the branching point, which would be possible in the case of stop branching. Three types of leak branching are possible in the LM Ericsson 120 and 480channel systems: — branching for direct termination, fig. 10 — branching for remote termination, fig. 11 — remotely fed branching terminal, fig. 12.
Fig. 14 Interiorview of a repeater station with a branching hybrid for re mote termination Fig. 15 Portable carrier frequency service telephone Branching for direct termination implies that a desired frequency range in the line group band is terminated in a station with local power, which is in direct connection with the main line. This station can be arranged for traffic in one direction or both directions. The equipment that needs to be added to the main lineconsistsof a passive branching unit. The advantage of a passive unit is that a power failure in the local station does not affect the main line traffic. The frequency range of the line group band that is used for branching varies depending on whether the connected terminating equipment is equipped with subgroups, groups or supergroups. The carriers required can be generated from a basic frequency of 124 kHz, which is regenerated from the line pilot of the system. The station will thus be fully synchronized with its main station. Branching for remote termination means that the station for the branched traffic is situated so far from the main line that line repeaters are required in the branched line. The equipment that is required in the main line is a passive branching unit in this case also, and it is placed in the same housing as the line 103 repeater of the main line, fig. 14. The remote power in the main line is not affected by the branching and the line repeaters in the branched line are power fed from the terminating station. Remotely fed branching terminal means that the station for the branched traffic is powered from the power feeding on the main line. The station is installed in a sealed housing designed for burying in the ground, and can be equipped for up to 12 telephony channels with 4-wire or 2-wire termination with E and M signalling. Three channels can be provided with subscriber signalling units. In this case also, the carrier generation is based on regeneration from the line pilot. In this case the terminating group is placed in supergroup No. 2. The station is powered through a special DC/DC converter, which from the constant current of the remote powerfeeding gives a constant voltage of 12 V. A fault in the terminating equipment will not affect the traffic in the main line in this branching case either. The number of remotely fed branching terminalsthat can be arranged along a line is of course
Page 1: ERICSSON REVIEW 3 1978 COLOUR DISPL
Page 4 and 5: Colour Display System SEMIGRAF 240
Page 6 and 7: 88 Fig. 4 The three beams red, gree
Page 8 and 9: 90 Fig. 8 Keyboard for SEMIGRAF 240
Page 10 and 11: Operational Experience of ANA 30 in
Page 12 and 13: 94 Fig. 3 Changing subscriber categ
Page 14 and 15: New Generation of 120 and 480-Chann
Page 16 and 17: 98 Fig. 3 Translation of basic supe
Page 18 and 19: 100 Fig. 6 Line terminating shelf s
Page 22 and 23: Fig. 16 Housing for one line repeat
Page 24 and 25: AXB 20 - Operation and Maintenance
Page 26 and 27: Fig. 4 Display terminal connected t
Page 28 and 29: 110 Fig. 8 Procedure for changing d
Page 30 and 31: System data for AXB 20 Application
Page 32: TELEFONAKTIEBOLAGETLM ERICSSON ISSN

Colour Display System SEMIGRAF 240 - The history of Ericsson

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