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Terminal repeater Cable Dependent repeater Cable Dependent repeater } ^ q Recorder Fig. 4 Block schematic of h.f. line equipment for small-diameter coaxial cable A B C D E F G H K LL L2 La Equalization network for station cable Pilot suppression filter Mop-up equalizer on send side, if required Pre-emphasis network Pilot generation equipment Generation of test frequencies for supervision of intermodulation De-emphasis network Equalization equipment Line amplifier unit Equipment for frequency comparison pilot Pilot receiver for supervision of a line section Noise blocking receiver L* Receiver for supervision of intermodulation M Maintenance test point P Remote power feed unit Ref. Reference voltage Type A has been considered the best and is the standard type in Sweden. The reasons for this are its good impedance characteristics and high dielectric strength, and the anticipated better crosstalk characteristics, since the copperplated steel strips ensure good electrical connection across the slit in the outer conductor. This is important having regard to the future extension of the small-diameter coaxial system to 12 Mc/s. L M Ericsson's h. f. line equipment is designed for use in conjunction both with type A and type B. Fig. 3 shows the attenuation per kilometre at + 10° C for type A as function of the frequency. Repeater Spacing One of the most important factors in the economy and technical performance of a h. f. line is the choice of repeater spacing. This has been made 8 km for the 300-channel system having regard to the available repeater elements, remote power supply, and future convertibility. When converting to a larger system it is convenient to halve the repeater spacing and the following series of systems is realized: Repeater spacing 8 km 4 „ 2 „ System 300 channels 960 2700 Bandwidth 1.3 Mc/s 4.2 „ 12.4 „ These numbers of channels are in full accordance with what has already been standardized for the 9.5 mm coaxial cable. At its last plenary meeting C.C.I.T.T. also standardized 4 km as repeater spacing for 960-channel smalldiameter coaxial cable svstems. Electrical Features of the Line Equipment Fig. 4 shows a block schematic of a terminal repeater station and two intermediate repeater stations with remote power supply. In broad outline the arrangement is the conventional one for a four-wire coaxial cable system. 80
Signal level dbr * u -20 "-^ri*r-LQi m^E fW Fig. 5 Relative levels within the line repeater for 1.3 Mc/s system 1 i 60 100 400 700 1000 1364 • kc/s The function of the intermediate repeater is to compensate for the attenuation of the signal over a cable length equal to the repeater spacing, in the 1.3 Mc/s case 8 km, corresponding to 49.2 db at the highest frequency. The required gain curve is achieved by a combination of a three-stage amplifier, the gain of which rises with the frequency, and a special gain equalizing network at its input. The dependence of the gain on the frequency is achieved by means of negative feedback which varies with the frequency. This is essential to the use of pre-emphasis in the system and thus has a great significance on the repeater spacing that can be achieved with given types of transistors. Fig. 5 shows the level conditions in the 1.3 Mc/s repeater. A three-stage amplifier was chosen since it is the type which makes best use of the transistors. Each intermediate repeater is equipped with automatic level regulation under the control of the main pilot. Owing to temperature variations in the soil the cable attenuation varies by about 2"/oo per °C, which for the 1.3 Mc/s system and ± 10° C represents about ± 1 db per repeater section. For this purpose regulation at each third intermediate repeater station would be acceptable, but great advantages are gained by providing each intermediate repeater with a pilot receiver. Each regulator has a range of ± 4 db. Of this quantity ±1 db is allotted to temperature correction as noted above. The remaining ± 3 db can then be allocated as follows: • ± 1 db for manufacturing tolerance of the cable. • ± 2 db can be used to take up tolerances in the length of repeater sections, which in the 1.3 Mc/s case corresponds to about ± 300 m, without needing to lengthen the cable. This principle results in simplification of the installation work and eliminates the need for different types of amplifiers. On replacement of a line amplifier no adjustment of the gain need be made. If desired, the manufacturing tolerance for the cable and the repeater section tolerance can be eliminated at the time of installation. The entire regulating range of ± 4 db is then available for temperature correction, which means that overhead cable can be used. 81
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Page 4 and 5: L M Ericsson's H. F. Line Equipment
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Page 12 and 13: • The four-wire circuit permits a
Page 14 and 15: Fig. 12 Example of connection of ma
Page 16 and 17: AKD 735, Code Switch P.A.B.X. for 3
Page 18 and 19: Recall to operator. If an incoming
Page 20 and 21: Rack The rack has a light-grey enam
Page 22 and 23: The tones are generated by a transi
Page 24 and 25: Common night service. The operator
Page 26 and 27: Radio Alarming of Fire Brigade ANDE
Page 28 and 29: The system in its present form cons
Page 30 and 31: Aerial There is very little possibi
Page 32 and 33: Telephone Jubilee at Ericsson do Br
Page 34 and 35: G. H. Wieneke in Memoriam After a b
Page 36: The Ericsson Group Associated and c

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