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8 30 Fig. 7 Line repeater with pilot regulation Both amplifiers are constructed in the hybrid technique, and in each of them thick film technique is used for the active parts and most of the feedback network. This gives a short feedback loop and a small phase shift. A conventional pre-equalizer in the preamplifier shapes the gain curve at low frequencies and power separation filters at the input and output separate and combine the HF signals and the power feeding. A line building-out network provides simulated cable attenuation of up to 22 dB, i.e. almost a whole repeater section. The line building-out network can be placed in any line repeater. Parallel feeding is used for the power feeding of the line repeaters in such a way that one zener diode feeds both transmission directions, but with a separate diode for the pre-amplifier and the power amplifier respectively, fig. 6. This feeding method requires double the current but only half the voltage of series feeding, and hence almost twice the number of line repeaters can be fed with this method. This is particularly desirable in a 60 MHz system since the distance between the line repeaters is short. The line repeaters are well protected against external electrical disturbances taken up by the cable, such as lightning pulses. Gas discharge tubes with a striking voltage of 1400 V are provided at the input and output of the repeaters, between the inner conductor and earth. The limit frequencies for the power separation filters are chosen so that as little as possible of the energy in the lightning pulse gets into the amplifier part. The input and output of the amplifier part are also provided with diode chains and each transistor is protected by a base-emitter diode. Thus a whole series of protective circuits combine to give the greatest possible operational reliability. Line repeater with pilot regulation The line repeater with pilot regulation has the same construction as the repeater with fixed gain, except that a regulating circuit has been added. This circuit consists of a pilot receiver equipped with a digital memory and a thermistor. The gain is regulated automatically with the aid of the 61160 kHz pilot so that the level at the output of the line repeater is always held at the nominal value, fig. 7. The regulation process is as follows: The pilot signal is extracted at the output of the power amplifier with the aid of a crystal filter and is then amplified and rectified. The pilot voltage thus obtained is compared with a constant d.c. voltage in an operational amplifier. The voltage difference determines the amount of current through an NTC thermistor placed in the series branch of the pre-amplifier feedback network. If the pilot fails, a digital memory takes over the control of the thermistor with the same current that existed immediately before the loss of the pilot. The gain conditions that applied will then be maintained until the pilot returns. The memory circuit consists of an 8-bit shift register, with the aid of which the thermistor current can be reproduced so that the regulation range is divided into steps of 2 mB. The regulation range at 61160 kHz is ±3 dB, of which approximately ±2 dB is used for variations in the cable at- Fig. 6 One direction ot the regulating line repeater. The zener diodes teed the corresponding part in the other direction PRA Pre-amplifier POA Power amplifier PR Pilot receiver
31 Fig. 9 Regulation range for the main regulating pilot 61160 kHz tenuation caused by temperature changes, and ±1 dB for variations in length when installing the regulating line repeaters, fig. 9. All gain variation as a result of the regulation takes place in the pre-amplifier. Terminal repeater The levels between the cable side and the line terminating equipment are adjusted with the aid of a terminal repeater, which on the send side has the same design as a line repeater with fixed gain and on the receive side the same design as a repeater with pilot regulation. The transmission band is thereby regulated before equalization. A de-emphasis network on the output gives the desired flat level. An alarm circuit senses the level of the 61160 kHz pilot at the output of the power amplifier, and if the deviation after regulation exceeds a preset value, which can be set to ±0.7, ±1.2 or ±1.7 dB, an alarm is obtained. A separate outlet is provided, to which a recorder can be connected for continuously monitoring the pilot level. In order to avoid having too high a voltage in the terminal bay the terminal repeater is not fed with power from the remote power feeding system that feeds the remaining line repeaters. The terminal repeater is instead fed from a local 21 V d.c. converter. Power feeding The equipment can be fed with power from a 24 V, 36 V, 48 V or 60 V station battery. It can also be fed from the mains via a mains rectifier that gives a d.c. voltage of 41-72 V from 110 V or 220 V a.c. The mains frequency is allowed to vary between 45 and 65 Hz. The output power from the rectifier is 440 W. Fig. 8 Line repeater with amplifier part, pilot receiver and power separation filters
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: PER-ALRIK HALLBERG THORWALD LUNDMAR
Page 37 and 38: Fig. 12 Power feeding of the line r
Page 39 and 40: 35 oscillators also cease operating
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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