ERICSSON REVIEW

2 1988

DIALOG 2000 - A New Family of Telephone Sets Subscriber Multiplexers in the Swedish Network Components and Systems Applications in Integrated Optics Wavelength Division Multiplexing over Optical Fibre MINI-LINK Mk II - A New Member of the MINI-LINK Family Solar and Wind Power - Experience Gained in Argentina

ERICSSON REVIEW Number 2 1988 Volume 65

Responsible publ isher Gosta Lindberg

Editor Goran Norrman

Editorial staff Martti Viitaniemi

Subscr ipt ion Peter Mayr

Subscr ipt ion one year 20

Adress S-126 25 Stockho lm, Sweden

Published in Swedish, Engl ish, French and Spanish with four issues per year

Copyright Telefonakt iebolaget LM Ericsson

Contents 46 • DIALOG 2000 - A New Family of Telephone Sets

51 • Subscriber Multiplexers in the Swedish Network

56 • Components and Systems Applications in Integrated Optics

64 • Wavelength Division Multiplexing over Optical Fibre

69 • MINI-LINK Mk II - A New Member of the MINI-LINK FAMILY

75 • Solar and Wind Power - Experience Gained in Argentina

MINI-LINK Mk II is a member of Ericsson's family of compact radio links. Compared with older members of the family it offers more installation possibilities and better and more comprehensive operation and maintenance functions. It also utilizes the frequency spectrum more efficiently

DIALOG 2000 - A New Family of Telephone Sets

Olle Larsson and Toivo Wiklund

In 1987 Ericsson Business Communications AB Introduced a new family of telephone sets under the collective name of DIALOG 2000. The first sets on the market have an analog interface towards the line. They offer a wide range of user facilities. A new mechanical design of telephone sets, in three different sizes, has been developed for DIALOG 2000 This design is also used for telephones with a digital interface.

The authors describe the analog telephones, their various functions and the new design.

telephone sets packaging design engineering

When the first DIAVOX telephone was introduced in 1978 its predecessor was already fifteen years old. When Ericsson Business Communicat ions AB launch­ed DIALOG 2000 in 1987 only nine years had passed since the introduct ion of DIAVOX. The trend is clear; the life of each type of telephone set is becoming shorter. New generations are needed to meet the current demands as regards design and functional i ty.

Market requirements as regards design and funct ion have guided the develop­ment of DIALOG 2000 together with the need to use modern component tech­nology and manufactur ing methods. At the launch of DIALOG 2000 the range comprised four telephones with an ana­log line interface and different func­tions. Later telephones with a digital in­terface, for the business communica­t ions system BCS 150, were added and during 1988 the range wil l be further ex­tended by telephones with various facili­ty levels for the digital PABX MD110.

Design External design is an important aspect of the development of new telephone sets. Users have opinions and demands as regards - the appearance of the set - user-friendly design of the handset - user-friendly design of the push-but­

ton set.

Fig. 1 The DIALOG 2000 family contains telephone sets for several different applications

OLLE LARSSON TOIVO WIKLUND Ericsson Business Communication AB

47

The manufacturing process makes de­mands on the design in terms of - flexibility, so that the telephones can

be used in several markets and in dif­ferent applications

- adaptability to modern manufactur­ing methods with a high degree of mechanization.

During the development of DIALOG 2000 a number of basic requirements were formulated which meant that - all telephones, whatever the facility

level and type of interface, must con­stitute a uniform family as regards colour, appearance and handling

- the design must be economically correct both mechanically and with respect to user procedures

Fig. 2 Exploded view of the new telephone, size II

- the body of the set must be small and low

- the high quality of the sets must be emphasized by the exterior design

- the design must be suited to modern manufacturing technology

- the sets must match office products from other Ericsson companies.

Several design companies were invited to submit proposals for the exterior of the telephone sets. Roland Lindhe De­sign AB presented the overall best solu­tion and was given the task of designing the exterior of the new family of tele­phones.

Mechanical design and components A new construction practice has been developed for DIALOG2000, actually in three sizes in order to facilitate optimum design of all sets in the family, fig. 2.

Great attention was paid to making the body of the set stable and the handset rigid, with torsional strength. The dif­ferent parts of the set fit together in such a way that they form a shell with internal supports. As a consequence the set can withstand a fall from the top of a desk without any damage. The material in all outer parts is matt ABS plastic with high resilience to impact and scratching.

The design is very flexible so as to meet the requirements of different markets. This applies especially to the keyset panel, whose buttons and controls can be labelled in different languages.

The smallest size of the new telephones has the cover and keyset panel moulded in one piece. For technical reasons, per­taining to the manufacturing process, the other two sizes have a separate key­set panel which is fitted to the cover.

The keyset panel consists of a frame, an antistatic plate, a contact pad and a printed board assembly The parts are riveted together after testing and so form a sealed unit. The contact pad, made of silicone rubber, has a dual func­tion: as a contact and a return spring for the buttons. The printed circuit board

48

holds the rest of the contact elements whose contact material is carbon. Sur­face-mounted components can be placed on the underside of the board, e.g. for keyset decoding.

The keyset frames can be equipped with an optional number of buttons depend­ing on the type of set. The maximum number of buttons for the three sizes is 25, 39 and 60 respectively. LEDs can be fitted in 7, 21 and 35 button positions.

There are two types of cover for each of the two larger sizes: for sets with and without a display. The display, when provided, is mounted in a separate unit which is adjustable to five positions so as to avoid reflections and give better legibility.

The handset is designed in accordance with international standards for acous­tic properties and handling. It contains an electret microphone with RF noise suppression and an electromagnetic re-

Fig. 3 Analog standard telephone sets

ceiver. The handset can be equipped with a press-to-talk or privacy key.

The signalling device is a piezoceramic tone ringer fixed to the base of the tele­phone. In sets equipped with a loud­speaker the latter is also used as a ringer device.

The telephone can be equipped with printed board assemblies of optional sizes. The space between the board and the base allows surface-mounted com­ponents on the underside of the board.

In addition to the electronic compo­nents required for the set in question, the printed circuit board also holds gen­eral electromagnetic components, such as a hook switch assembly, switches for the pitch and volume of the tone ringer, a switch for pulse or DTMF signalling, potentiometers for the control of re­ceiver gain and loudspeaker volume, and various connectors.

The electronic components are dif­ferent in the different types of tele­phones. Analog sets contain a transmis­sion circuit, DTMF/pulse signalling cir­cuit and tone ringer circuit; all ICs. Tele­phones for digital systems contain transmission circuits specific to the sys­tem, together with codec and filter cir­cuits. Sets with special facilities also contain memory circuits, an operational amplifier, a speech control circuit and a microprocessor.

Common features All telephones in the DIALOG 2000 fam­ily have the following features: - they can be mounted on the wall by

means of a special bracket, common to all three sizes

- both the telephone and the handset cord are connected via a plug and jack for easy replacement

- they can be equipped with adjustable extra amplification of the sound in the receiver

- text and symbols on the set can easily be customized with the aid of the des­ignation board

- a headset can be fitted instead of the handset.

49

Telephone types Standard sets The first DIALOG2000 telephones to be marketed have an analog interface. They are designed to be connected to PABXs and public exchanges with ana­log lines. Four different types have been developed, f ig3 : - the basic sets DIALOG 2103 and

DIALOG 2104 - DIALOG 2137, a set with few facil it ies,

primarily single-button call ing - D I A L O G 2 1 6 6 , a multi-facil i ty set

providing single-button cal l ing, dis­play and speech-control led loud-speaking funct ion

In addit ion to the common features the basic sets are equipped with a tone ring­er having four-step adjustment of both volume and tone pi tch.

DIALOG2103 has only DTMF signall ing andean be equipped with a recall button for earth signal or t imed break register cal l ing.

In DIALOG 2104 the signall ing mode can be switched between DTMF and decadic impulsing, and the set also includes a memory for the last number dialled, f ig.4.

DIALOG 2137 offers single-button call­ing, which means that when the receiver is lifted and the appropriate button is

depressed the telephone automatically transmits the whole number. The set has ten buttons for this funct ion and is powered entirely from the line, so no battery is required.

DIALOG 2166 is a multi-facil i ty set with such funct ions as: - speech-control led loudspeaking

funct ion, which allows the user to have both hands free for work dur ing calls

- nine single-button call ing numbers with automatic connect ion to the line. When one of these buttons is de­pressed the telephone is switched to the loudspeaking mode and the num­ber is dialled automatical ly

- three extra memories in which the three last numbers dialled are stored for the user to connect himself to as required. When a number has been chosen it is called automatical ly by depressing one button

- fifty memory posit ions, which are ad­dressed by two-digit abbreviated numbers for automatic call ing

- programmable volume and tone pitch for the tone ringer

- a display that shows the dialled sub­scriber number and programming state

- volume control for the receiver and loudspeaker

- power feeding f rom the line, render­ing batteries unnecessary.

Fig. 5 Telephones for the digital business communica­tions system BCS150

Fig 4 DIALOG 2104 mounted on a wall

50

Fig. 6 Telephones for the digital PABX MD 110

Telephones for digital systems The telephones for business communi ­cations system BCS150, f ig. 5, and the digital PABX MD 110, f ig. 6, also have the features common to all DIALOG 2000 sets. In addit ion they have a large num­ber of facilit ies specific to the system in question. However, the sets can be di­vided into the fo l lowing general types:

- basic sets and sets with few facilit ies. These have up to five programmable keys, receiver amplif ier and a tone ringer with adjustable volume and tone pitch

- medium-facil i ty sets which in addi­t ion have a monitor ing loudspeaker, 10 -12 programmable keys and triple access line

- multi-facil i ty sets, which in addit ion to the basic funct ions mentioned above have a speech-control led loud­speaker, a display and 12 or 26 pro­grammable keys.

Summary With the launching of DIALOG2000 Ericsson can offer a wide range of very competit ive telephones for home as well as office use. The sets can be connected to both public and private networks. The use of a common, standardized con­struction practice and custom inte­grated circuits has resulted in tele­phones with - small volume and low height - user-friendly procedures and fun-

tions - ergonomic design of control devices

and display unit - high reliability and environmental en­

durance and a long mechanical life.

References 1. Boeryd, A. and Wiklund, G.: New Tele­

phone Set. Ericsson Review 54 (1977):3, pp.112—113.

2. Reinius, J. and Sandstrom, O.: DIA-VOX Courier 700, Digital System Tele­phone for MD 110. Ericsson Review 59 (1982)2, pp. 58-66.

3. Jansson, U. and Larsson, O.: DIA-VOXCourier605. Ericsson Review 61 (1984):3, pp. 114-118.

Subscriber Multiplexers in the Swedish Network

Stefan Davidsson, Lennart Johansson and Erling Ohlsson

Since 1983. the Swedish Telecommunications Administration has used Ericsson's digital subscriber multiplexers (RSM CSM) to connect ordinary telephone sets to the analog telecommunications network. The Administration also wanted conversation time limiters. coin-box telephones and PABXs to be connectable in the same way. and Ericsson has now modified RSM CSM accordingly. RSM can be supplemented with the functions required for the equipment mentioned above. It is also possible to replace some of the line circuits in an RSM with a repeater for signalling between exchanges, while the other line circuits are used to connect ordinary telephones.

The authors describe the advantages of the upgraded RSM CSM and some applications in the Umea telecommunications area and discuss the operational experience gained.

multiplexing equipment maintenance engineering testing telephone networks

Both the remote subscriber multiplexer, RSM, and the central office subscriber multiplexer, CSM, have been described previously in Ericsson Review.1 An RSM can connect up to 30 subscribers to a digital AXE10 exchange via a 2Mbit /s interface and a digital line system. The transmission medium can be paired ca­ble, optical cable or a radio link. If the subscribers are to be connected to an analog exchange it is necessary to place a CSM between the line system and the exchange. RSMs can be provided with equipment for testing lines and line cir­

cuits. Tests can be initiated either auto­matically or manually f rom AXE 10 or CSM.

The Swedish Telecommunicat ions Ad­ministration uses the designation PMA for the funct ion connect ing a subscriber via a digital multiplexer. The need for subscriber mult iplexers arose at the end of the 1970s when digital ization of short-distance routes in the junct ion network started. The first PMA equipment con­sisted of a combinat ion of separate PCM mult iplexers and subscriber repeaters (ZAS01-7) placed in cabinets indoors or outdoors They were tested by the Administrat ion together with line sys­tems over optical cable and special paired cable for PCM circuits.

New demands on RSM/CSM Surveys carried out by the telecom­munications areas when PMA became available showed a need for greater flex­ibility so that the fo l lowing requirements could be met: - It should be possible to connect

PABXs with single-wire signall ing and/or direct in-diall ing via PMA

Fig. 1 Rural exchange

LENNART JOHANSSON Swedish Telecommunications Administration STEFAN DAVIDSSON ERLING OHLSSON Ericsson Telecom AB

Fig. 2 Umea telecommunications area

- It should be possible to connect aux­iliary equipment, such as con­versation time limiters, subscribers' check meters and coin-box tele­phones, via PMA

- It should be possible to mix line cir­cuits for the connection of telephones with circuits that function as repea­ters for signalling between ex­changes - FUP, FIP, E&M - in the same magazine. The 30 RSM chan­nels can then be divided so that some are used for subscriber lines and the rest for junction circuits with DC loop or E&M signalling

- It should be possible to use different digital signalling diagrams for the conversion between analog and digi­tal signalling. Then Ericsson's digital signalling diagram could be used for general RSM/CSM applications and the Administration's digital P7 or P8 in special cases, such as the connec­tion of analog PABXs to the digital group switch in AXE 10 or of digital PABXs to analog exchanges

- It should be possible to connect leased lines, for example point-to-point circuits and different types of data circuits, via PMA.

System design In order to meet the demands for greater flexibility the system design has been modified as follows: - The existing RSM and CSM systems

are basically unchanged - The additional line circuit functions

necessary when a PABX with single-wire signalling or direct in-dialling is to be connected to an RSM have been placed on a separate board, the PABX interface unit. The boards are in­stalled in a magazine of their own, the RSM PABX signalling magazine. A generator for the transmission of a 12kHz or 16kHz signal to subscrib­ers' check meters and a generator for a 425Hz ringing tone can also be placed in this magazine.

- The additional line circuit functions required in CSM, if the above-men­tioned types of PABX are to be con­nected via PMA to an analog ex­change, have been placed on a sepa­rate board, the B-wire grounding unit. Such boards are installed in a maga­zine of their own, the CSM PABX sig­nalling magazine.

- Three new line circuit boards, FUP, FIP and E&M, having the same func­tions as repeaters for signalling be­tween exchanges, have been de­veloped. They are placed in the ordi­nary RSM and CSM magazines and can be mixed with the ordinary line boards. All these boards are equipped with a terminating set for the con­version to a four-wire speech path. The path is connected to the channel units in the PCM multiplexer via the wiring side of the magazine.

- A new signal control unit, based on a microprocessor, for the control of the line circuits has been developed. The microprocessor controls the con­version between analog and digital signals. The signal control unit is the same regardless of the function of the system, i.e. whether it is used as an RSM, CSM or FUP, FIP or E&M multi­plexer. The control unit senses the types of board installed and selects the appropriate conversion process. The signal control unit in RSM also controls the line circuits in the RSM PABX signalling magazine. A cable is then run from the front connector of the control unit to the magazine, fig. 3. In a similar way the CSM signal control unit controls the line circuits in the CSM PABX signalling maga­zine, fig.4.

- The additional RSM line circuit func­tions for such equipment as con­versation time limiters, subscriber's check meters and coin-box tele­phones are located on a separate board, the SE-RCIC unit. Such boards are mounted in a magazine of their own, the RSM SE-RCIC signalling magazine. The SE-RCIC unit is con­nected to the line circuit boards in RSM via cables to the front con­nectors. Charging pulses can be transmitted from the public exchange via RSM to the same types of auxiliary equipment that are normally con­nected directly to the public ex­change.

Advantages of RSM/CSM Economy and complexity There are major advantages in using RSM and CSM instead of combining separate PCM multiplexers with signal­ling equipment, particularly in cases where the number of subscribers is small. When separate equipments are

Fig. 3 The connection of the RSM PABX signalling magazine to the RSM magazine

Fig. 4 The connection of the CSM PABX signalling magazine to the CSM magazine

used it is usual for the PCM multiplexers and signalling equipment to be installed in different racks which is not the case with RSM and CSM. In the subscriber multiplexers the four-wire interface is placed at the wiring side of the maga­zine. Hence, there is no need for sepa­rate four-wire connections between the multiplexer and the signalling equip­ment. Such four-wire connections are often run via a main distribution frame. Consequently, the RSM/CSM equip­ment has advantages with respect to in­stallation, space and economy Savings vary with the application but are esti­mated to be approximately 45-75% for installation and up to 50% as regards space and costs.

Connection of rural exchanges via RSM/CSM RSM/CSM provides an excellent solu­tion when problems arise in rural ex­changes as regards capacity, quality and shortage of numbers. Often no more than 30 junction lines are required between a rural exchange and the par­ent exchange. With RSM/CSM the need for junction lines for a 60-subscriber rural exchange can be met by 8-14 cir­cuits. The remaining 16-22 line circuits in the RSM can then be used to connect subscribers direct to free numbers in the parent exchange, which could solve the problem of number shortage in the rural exchange. Companies and other major users who have been connected to the rural exchange can have direct lines to the parent exchange. They will then not

load the junction lines to the rural ex­change and will also have access to fa­cilities that the rural excange cannot provide, such as group numbers for PABXs and data network services. Umnas in the county of Vasterbotten is one exchange where RSM/CSM have been used in a way similar to the one described here, fig.5. If the parent ex­change is an AXE 10, such AXE services as DAMAXE and CENTREX are avail­able.

Cheaper cable maintenance Today, many cables require quite an amount of maintenance if a satisfactory transmission quality is to be preserved. Digital circuits are less sensitive to inter­ference, crosstalk and other quality problems than analog circuits and, hence, the amount of cable mainte­nance required is less when PCM is used. The potential savings can be turn­ed into cash only if PCM is used for all circuits in the cable, however.

The upgraded RSM/CSM has greatly in­creased the possibilities of improving quality through reducing the need for investment when converting to PCM. The opportunity for mixed equipping plays a major part. When physical cir­cuits in a cable are replaced, for reasons of maintenance or capacity, by radio links or optical cable the result is that all channels must be transmitted via PCM. RSM/CSM then often provides the best solution. Figs. 6 and 7 show networks where cables with high maintenance re-

Fig. 5 Application featuring RSM/CSM with mixed equip­ping

Digital line system

54

Fig. 6 The system comprises six RSM and six CSM magazines equipped with FIP/FUP boards. The system has spare capacity which can be used to connect subscribers at the subordinate ex­changes direct to Savar. The total length of the digital route is approximately 35 km

Fig. 7 The system comprises six RSM and six CSM magazines with E&M boards mixed with subscrib­er boards. When A204 is converted to AXE 10 all subscribers will be connected to AXE 10 via the RSM magazines, and the rural exchanges (Std41) will become redundant. The subscribers will then have access to the AXE 10 services. The total length of the optical route is approximately 45 km

quirements and low capacity have been equipped with PCM systems or replaced by optical cable.

Network coordination benefits In order to reap the benefits of coordina­tion when running optical cable for long-distance or cable-TV networks, 2Mbit/s tributaries are branched off a-long the cables. The tributaries can be used for circuits in the short-distance network. In the example in fig. 7 several branches have been arranged along a 34 Mbit/s line system from an analog ex­change (A204). The tributaries are termi­nated in RSMs equipped with boards for E&M signalling, which provides junc­tion circuits to rural exchanges (Std41). Coordination benefits are obtained in both the long-distance and short-dis­tance networks, and in the latter both for junction and subscriber lines thanks to the flexibility of the RSM. A similar ar­rangement has been made for the Umea AXE 10 exchange, fig. 8. In this case the RSM is connected to the digital group switch in AXE 10. The RSM is equipped with FIP/FUP boards for the circuits be­tween AXE 10 and A204 and Std41, and also between two A204 exchanges.

Testing and operational experience Testing FIP/FUP boards in RSM/CSM When evaluating systems for the optical network to the Umea AXE 10 exchange,

fig. 8, and the network to the Savar A204 exchange, fig. 6, it was found that RSM/ CSM with FIP/FUP would be the least expensive system. The FIP/FUP boards had been developed when the tender was made, but had not been tested in the exchange systems concerned. The nec­essary tests were carried out during the autumn of 1986 jointly by the Umea tele­communications area and Ericsson Most of the RSM/CSM magazines were taken into service during the spring of 1987 and the rest in the autumn. The operational experience of FIP/FUP in RSM/CSM has been very good. Some faults were discovered during the tests. Only a few more faults were found when the equipment was put into operation. All faults concerned the signalling and were quickly corrected by means of pro­gram modifications in the signal control unit.

Trial with outdoor cabinets When the Swedish Telecommunica­tions Administration started using PMA the equipment was installed in cabinets. Lacking sufficient experience of elec­tronics installed outdoors, the Admin­istration placed a PMA in an outdoor cabinet in the Umea telecommunica­tions area. The equipment has been in operation since 1980. Experience shows that PMA can be placed outdoors without any major disadvantages as re­gards operation and maintenance. The very few service irregularities that have occured have been caused by over-dis­charging of the battery due to power failures of some duration. The power supply equipment has now been provided with a battery disconnection function that eliminates the risk of over-discharging.

In order to gain more experience of the performance of the equipment out­doors, two RSMs were installed in out­door cabinet BYB 905 in 1983, one in the town of Umea and one on the outskirts. The cabinets, which consist of an inner cabinet and an outer cover, have no

34 Mblt/s line system over optical cable with digital multiplexers with branching facility

Digital line system

Fig. 8 Optical network with RSM connection to the Umea exchange

heating. The temperature dropped to -35CC occasionally, which meant that the RSM equipment worked below the specified lower temperature limit. In order to avoid this the cabinets installed in 1987 have been equipped with a ther­mostat-controlled heating bar. Experi­ence gained from the earlier installa­tions has also led to the modification of other details. Both the inner and outer cabinets have been provided with doors instead of the previous lids hinged at ttie top. The cabinets have thereby been im­proved both as regards working condi­tions and safety.

Summary During 1987, some RSM/CSM maga­zines for different applications have been installed in the Umea telecom­munications area. Project planners, in­stallers and operating staff have all found the equipment easy to handle. The operational experience of the ap­plications concerned has been very good. Few faults have occured, and the great flexibility of the RSM/CSM maga­zines has meant that alterations caused by new subscriber requirements have been more easily effected, both prac­tically and economically.

Fig. 9 RSM installed in an outdoor cabinet

References 1. Larsson, C. and Olsson, E.: Remote

Subscriber Multiplexer, RSM. Erics­son Review 60 (1983):2, pp. 58-65.

34 Mblt/s line system over optical cable with digital multiplexers

Components and Systems Applications in Integrated Optics

Anders Djupsjobacka, Per Granestrand and Lars Thylen

The rapid breakthrough and expected dominance of fibre optics in the transmission field has led to greater interest in opto components also for switching eguipment in the communications systems. Opto components in this application would make it possible to retain the large bandwidth of the transmission systems throughout the circuit, from terminal to terminal. Integrated optical components are now available for many functions which, so far. have been realized only through electronic components. The authors describe some integrated optical components developed by Ericsson and their applications in systems.

integrated opt ics integrated optoelectronic computer interfaces semiconductor |unct ion laser

Fig. 1 An example showing some of the functions that can be integrated in a monolithic integrated optical circuit, IOC. All incoming channels are connected via optical waveguides on the chip to the switching matrix, SWM. which is used as a non-blocking cross-connection. The laser ampli­fier SCLA amplifies the light signal from SWM in each channel in order to compensate for losses in the circuit. The signal on one of the channels is wavelength division multiplexed.5 In this case it consists of two signals with the wavelengths /1 and i,2. Signal sbtgl2 is branched in the wave­length demultiplexer WDM and detected in the photo diode PD. It can be used to control SWM. The high-speed coupler SW is used either to branch incoming traffic on its waveguide to PD or to modulate light from the laser diode LD and thereby generate traffic out on its signal path. This is done bit by bit. The semiconductor material is InP since a laser diode, laser amplifier and photo diode are included. In this example the electronic control circuits SE have not been incorporated in the integrated circuit

The term integrated optics was coined in the 1970s to emphasize similarities to the better known integrated electronics technology. The term denotes the art or technology of designing, manufactur­ing and using integrated optical circuits. Integrated optical circuits are compo­nents manufactured through a planar process and in which active and/or pas­sive circuit elements are integrated on a chip. The active elements include modu­lators, switch matrixes and laser ampli­fiers and the passive ones include power dividers, WDM couplers and mode fil­ters.

Optical waveguide channels intercon­nect the circuit elements similarly to the way metallization is used in electrical ICs, fig. 1. A circuit with only optical de­vices is called an integrated optical cir­cuit, IOC. Recently attempts have been

made to integrate both electrical and optical switching elements on one and the same chip. Such a component is called an opto electronic integrated cir­cuit, OEIC. For example, a laser has been integrated with its electrical drive circuits. Compared with hybrid circuits the integrated optical circuits offer the same general advantages as electronic ICs. Low-cost mass production of com­plex circuits with reproducible data be­comes feasible.

The rapid breakthrough of fibre optics occurred in applications for the trans­mission of information over point-to-point circuits. It is only natural that the possibilities of processing information in its optical state, i.e. without con­version to electrical signals, should also be investigated. The optical medium al­lows the transmission and processing of signals of extreme bandwidth in time and/or wavelength multiplexed mode.

Components and subsystems based on integrated optics and optoelectronics can be used in both transmission and switching systems.

Optical components can be used on both the send and receive sides of opti­cal fibre transmission systems. On the send side there would be intensity mod­ulators in direct detection systems, and phase, amplitude or frequency modula­tors in coherent systems. On the receive side switching devices, local oscillators

Metal electrode

Light waveguide

Electrical connection

ANDERS DJUPSJOBACKA PER GRANESTRAND LARS THYLEN Ericsson Telecom AB

Fig. 2 An electric 8x8 "quadratic matrix" which in its function is equivalent to the optical switch matrix

and phase shifters could be used in co­herent systems. Detectors and control electronics could also be integrated on the receive chip.

Space division switching devices Three basic principles underlie switch­ing functions: space, time and wave­length division At present space divi­sion components are the only practical alternative for fully optical systems.

Space division optical switching de­vices have been tried in telecommunica­tions systems in applications such as: - cross connections for wideband sig­

nal routing - protection switching systems, which

are used to switch to standby lines - integrated wideband networks for fu­

ture applications with two-way video communication, TV distribution, tele­phony, data communications etc.

Ericsson has developed an 8x8 switch matrix in lithium niobate (LiNb03) with diffused titanium waveguide chan­nels.14 The matrix is strictly non-block­ing: a free input can always reach a free output wihout rearrangement, i.e. with­out existing connections having to be rerouted. Fig. 3 shows a switch matrix chip. The switching elements in the ma­trix consist of voltage-controlled direc­tional couplers.

Fig. 3 Ericsson's 8x8 switch matrix

The matrix contains 64 directional cou­plers which are controlled by voltages across eletrodes placed above the chan­nels. A directional coupler consists of two waveguides, channels, which are placed close to each other in an interac­tion region, fig.4 Light fed into one channel is gradually coupled overto the other channel in the interaction region. When all light has been coupled to the second channel the process is reversed and the light is coupled back to the first channel. The result is an oscillation of the light power between the two chan­nels in the direction of propagation. The distance required to couple the light completely from one channel to another is called a coupling length and is desig­nated Lc. The refractive index profile of the waveguide can be altered by electric fields set up in the interaction region of the chip by means of electrodes.

If the effective length L of the electrodes and the interaction region equals an even multiple of Lc, e.g. 2xLc, light fed into the upper waveguide 11 comes out on the upper waveguide U1, and light fed into 12 comes out on U2. The direc­tional coupler is then said to be in the bar state.

If the electrical field is changed it is pos­sible to obtain a state in which light fed into the upper waveguide 11 comes out on the lower waveguide U2 and light fed into 12 comes out on U1. The directional coupler is then said to be in the cross state. In order to be able to obtain these two states by applying different voltages across the electrodes, the effective length of the interaction region, L, has to be between one and three coupling lengths, LC<L<3LC. The directional cou­pler used in Ericsson's 8x8 matrix is of the type shown in fig.4, with L approx­imately 2 mm.

The directional coupler device can also be used as a modulator. The electrode

Fig. 4 Electrically controlled directional coupler with light waveguides and electrodes

Electrode

Waveguide

58

Fig. 5 Non-blocking Clos network

Fig. 6 4x4 strictly non-blocking polarization-indepen­dent switch matrix

has been designed as a transmission line for microwaves, a travell ing wave­guide, so that high modulat ion frequen­cies can be used.

A prerequisite for satisfactory funct ion of the directional couplers in the 8x8 matrix is that the polarization of the E-field of the incoming light is perpen­dicular to the surface of the chip. The reason in that the coupl ing length Lc is different for plane and vertically polar­ized light. The polarization also affects the change of the refractive index as a funct ion of the electrical f ield. Circuits requiring a specific mode of polariza­tion of the light are called polarization-dependent circuits.

In practice it is not possible to achieve complete coupl ing of all light in the bar and cross states: there will be a certain amount of crosstalk. In Ericsson's direc­tional couplers the crosstalk is typically < - 3 0 d B . After quadratic detection this corresponds to - 6 0 d B in "electr ical dB" .

The insertion loss of the matrix is ap­proximately 4.5dB when the signal pas­

ses through one directional coupler. Each addit ional coupler included in the signal path contr ibutes a further 0.1 dB (approximately), which means that the insertion loss of the longest path, which contains 15 direct ional couplers, is ap­proximately 6dB.

The voltage across the electrodes of the directional couplers is 20V. Both posi­tive and negative voltages are required, and it must therefore be possible to gen­erate ±20V.

Many appl icat ions need more than eight inputs and outputs. Larger systems can be formed by interconnect ing several 8x8 matrixes. In cases where not even brief interruptions of traffic in progress are acceptable a conf igurat ion can be used which gives a network that is non-blocking wi thout rearrangement, a Clos network, f ig. 5.

In large systems the insertion loss be­comes a problem. For example, a signal path in a Clos network must pass through several chips, and the available margin is soon used up. Another prob­lem is the increased amount of crosstalk obtained when the signals pass through many directional couplers. This prob­lem is emphasized if large differences in the power level of the incoming signals are al lowed. The crosstalk problem can be reduced considerably if more sophis­ticated network topologies are used.2

Polarization-independent lOCs for conventional fibre systems Ericsson's 8x8 matrix is polarization-de­pendent, i.e. the light fed into the circuit must have a certain, well-defined polar­ization. This requirement often applies to L iNb0 3 devices. A normal monomode fibre cannot maintain the polarization of the light as it is propagated along the fibre. This consti tutes a problem as inte­grated optics is often intended for use

Fig, 7 Block diagram of a transmitter with an external modulator. The transmitter was used in the Euro­pean collaboration project in which transmission systems tor 2.4 Gbits were studied. In the block Bias T a d.c. voltage is superposed on the modulating HF signal

Fibre

Electrical connection Electrical connections Optical connection

Table 1 Data of the externally modulated transmitter used in the European collaboration project in which transmission systems for 2.4 Gbit/s were studied. Data of a commercial transmitter with a bit rate of 600 Mbit s are included for the purpose of com­parison

2,4 600 Gbit/s Mbit/s

Wavelength 1,55 1,3/1,55 \im Type of laser DFB FP/DFB Pmean modulated -2,2 -3,0 dBm Destructive interference ratio 25 20 dB Modulation mode External Direct Input impedance 50 50 ohm Lower cut-off frequency 20 100+ kHz Upper cut-off frequency 2500 400+ MHz + The figures refer to the bandwidth of the receiver

with optical fibres. There are four basic solutions to the problem: - Polarization stabilization

The polarization state is stabilized by means of a regulating circuit. This method is based on the refractive in­dex being different for the two direc­tions of polarization and on control of the refractive index, e.g. by means of an electric field. It is then necessary to be able to measure the polarization state. This is no problem in some ap­plications; in others it is quite imprac­tical.

- Polarization-maintaining fibre This fibre maintains a linear polariza­tion state if it is correctly excited. The main disadvantages of this method are that the fibre is much more expen­sive than ordinary fibre and that it has not yet been used in any existing tele­communications system; neither is it likely to come into use in the foresee­able future. Another difficulty is that the fibre must be orientated to the correct angle of rotation around the symmetry axis of the fibre when it is spliced and attached to connectors.

- Polarization diversification Thesignal isdivided into two different polarization states, each of which is processed individually. This means that the system becomes more than twice as large, and in addition polar­ization-maintaining methods must be used in both parts.

- Polarization-independent compo­nents Integrated optical circuits with so­phisticated design can be made to work for both polarization states si­multaneously. The design takes into account the fact that the coupling length and the effect of the electrical field on the refractive index are dif­ferent for the two directions of polar­ization The disadvantages of such components are that the manufactur­ing tolerances are much narrower, higher operating voltages are nor­mally necessary and hitherto the crosstalk has been greater than in "ordinary" lOCs.

Ericsson has developed different types of polarization-independent directional coupler which have given good results in experiments. The electrodes are dif­ferent from those in the ordinary cou­pler in fig. 4. They make reasonable de­mands as regards manufacturing toler­ances, require only a moderate increase in the control voltage - a factor of 3 to 5 compared with polarization-dependent directional couplers- and give low crosstalk: - 24 dB for the two polariza­tion and the two switching states. The relatively mild requirements for man­ufacturing tolerances is because there is a certain amount of electronic tuning capability in the circuit. Ericsson has demonstrated, in march 1988, a polar­ization-independent strictly non-block­ing 4x4 switch matrix with a tree-struc­ture, fig6. The crosstalk in this device, which contains 24 directional couplers, was well below 35 dB. Due to the above-mentioned electronic tuning capability it was possible to reduce the require­ments for manufacturing tolerances. The switch matrix performs point-to-point switching as well as interconnec­tion of one transmitter with a number of receivers at the same t ime-commu­nicative and distributive switching.

2.4 Gbit/s system experiment with an external modulator During theautumn of 1987 Ericsson par­ticipated in an European collaboration on studies of transmission at 2.4Gbit/s. Ericsson contributed an optical fibre transmitter consisting of a DFB (Dis­tributed Feed-Back) laser with its reg­ulator system and a LiNb03 modulator, fig. 7. Table 1 gives data of the transmit­ter and a commercial system with a bit rate of 600 Mbit/s.

The transmitter was driven by a com­mercial drive stage which required an input signal of 1 Vp.p for full modulation of the modulator. The capacity of the externally modulated transmitter was estimated to be approximately 4Gbit/s.

Fig. 8, right Eye diagram for the externally modulated laser transmitter in fig. 7. Bit rate 4.0Gbit/s

Fig. 10, far right Received eye diagram for the externally modu­lated system. Bit rate 2.4Gbit/s. BER = 10 9. The measurement was performed by CNET

Fig. 9 Bit error rates obtained with Ericsson's externally modulated transmitter and a directly modulated transmitter respectively. Length of the fibre route = 40 km. The measurement was performed by CNET

Fig. 11 Bus chip. The diagram shows how the couplers S1 and S2 switch the data stream and the high­speed modulator XM modulates the light from the laser. In the passive state, the bypass function, the light passes straight through S1 and S2

Fig. 8 shows an eye diagram for the transmitter at 4Gbit/s.

On delivery the transmitter was tested with a receiver developed by CNET (Centre National D'Etudes des Telecom­munication) in Lannion. The results of the test were compared with those ob­tained when a directly modulated trans­mitter was used with the same receiver. The input sensitivity obtained with the externally modulated transmitter was -32.4dBm for 40km of fibre with a BER (Bit Error Rate) of 10 9. With the directly modulated transmitter the correspond­ing value was -28.3dBm. Thus, the ex­ternally modulated transmitter had bet­ter performance, mainly because of the absence of chirping. This is a phe­nomenon whereby, with direct modula­tion, the charge carrier dynamics give rise to a frequency sweep during the pulse. An eye diagram was recorded for the externally modulated system -transmitter + receiver - at 2.4Gbit/s. Fig. 9 shows BER curves and fig. 10 eye diagrams. The measurements were per­formed by CNET.

Optical fibre bus for 2.4 Gbit/s Local area networks, LAN, i.e. optical fibre communications networks within a

building or between adjacent buildings, can be configurated in different ways. The most common types are ring, star and bus networks. Integrated optical chips can be used in a LAN as controlla­ble drop points and access couplers. lOCs can also be used as bypass devices in point-to-point circuits. The bypass function increases both the flexibility and the reliability of a communications system.

Ericsson has developed a bus chip with bypass function, which can be used in a high-speed data bus for example. Fig. 11 shows the chip in a medium attachment node. The devices on the chip are two low-frequency directional couplers (S1 and S2) and a high-speed modulator for 2.4 Gbit/s (XM). When the data terminal connected via the node is in its active state, the incoming traffic-carrying sig­nal is connected via directional coupler S1 to a detector and subsequently de­multiplexed and processed. The termi­nal regenerates continuously the traffic to be sent on over the bus, branches off the part of the incoming traffic ad­dressed to itself and communicates the traffic it has generated. The outgoing traffic signal is generated in modulator XM and is fed through directional cou­pler S2 and out on the bus fibre. If a fault should occur in the data terminal the

Externally modulated transmitter

Directly modulated transmitter

Wideband amplifier

Optical Waveguide

Electrical connection

Electrode

Fig. 12 Measuring HF leakage In the bus chip of fig. 11. An optical pulse train was fed in on the incoming bus fibre; a, right, with modulation and b, far right, without any modulation in the high-speed modulator XM. The pulse train was recorded on the output detector fibre

incoming traffic bypasses the terminal - going through S1 and S2 direct to the output fibre - which means that the sys­tem, after resynchronization, remains in operation.

The attenuation of the bus chip is less than5dBfrom input to output. XM has a destructive interference ratio of better than 25dB and its driving voltage is 5.5VP.P The bandwidth of the modulator is 3 GHz. The directional couplers have a destructive interference ratio of better than 20dB and need a driving voltage of 79VP.P

The HF leakage between the circuit ele­ments is an important parameter for an integrated circuit with a high-speed modulator placed close to a low-fre­quency optical directional coupler. The HF leakage was measured in the follow­ing way. An electrical 2.4Gbit/s pulse train was fed into the modulator while a constant light level was maintained on

the incoming bus fibre. The HF leakage from XM to S1 was measured. The re­sults are shown in table2.

In the active state the signal level caused by HF leakage is 20dB lower than the level of the incoming traffic signal, which is sufficient for most applications.

The HF leakage was also measured as follows. An optical pulse train was fed into the optical fibre at the same time as another pulse train was fed into modula­tor XM. Fig. 12 shows the pulse pattern in the detector fibre when the chip is active; fig. 12a with and fig. 12b without a pulse train to the modulator. There are only minor differences between the two cases. The ringing to the left in the fig­ures was caused by the drive circuit.

The performance of the system at 2.4Gbit/s was simulated by calculating the eye diagram when the system's up­per cut-off frequency was 1.5GHz. The red colour in fig. 13 shows the eye dia­gram at 2.4Gbit/s and the blue colour the eye diagram for the system in ques­tion with a non-linear modulator. The eye diagrams show that the time the sig­nal is above 90% and below 10% is long­er for the non-linear modulator. It is therefore likely that non-linearity im­proves system performance.

Fig. 13 Calculated eye diagram for a linear modulator

Calculated eye diagram for the non-linear modu­lator in question. The system bandwidth Is 1.5 GHz in both cases

Table 2 HF leakage from XM to S1 in the bus chip of fig. 11

Chip state Active Faulty

HF power in detector fibre -20dB -21 dB output bus fibre -19dB -20dB

Fig. 14 The fibres to the integrated optical circuits are aligned with the aid of a microscope and micro-translators. The tolerance requirements are <1 nm

Fig. 16 shows the optical chip installed with the connections made to high and low-speed electronic circuits. The high-frequency bit stream comes in to the chip via a transmission line connected to the travelling-wave electrode on the chip. The low-frequency control signals are connected via an ordinary printed circuit board.

Laser amplifiers Amplification of light is a prerequisite for the construction of large systems, e.g. Clos networks, using LiNb03 cir­cuits without any conversion of the opti­cal signals into electrical form. This re­quires laser amplifiers. In its simplest form this amplifier consists of an ordi­nary semiconductor laser, whose ends have been coated with an antireflection (AR) substance. If a light signal issent in at one end the signal will be amplified in the medium that is created when the laser is pumped with current. In a light amplifier the gain normally obtained in the cavity formed between the ends of the laser is undesirable. In practice the

AR coating is, unfortunately, not perfect and a cavity is formed because of the residual reflectance at the ends. The am­plification will therefore vary with the wavelength of the light.

Another problem with laser amplifiers is that noise is added to the signal. Con­sequently, the amplifier works best at relatively high input signal levels. This requirement can be met in systems with LiNb03 circuits, since the attenuation in each chip is moderate.

Ericsson has built an experimental sys­tem which includes a directional cou­pler and an optical amplifier, fig. 17. A narrow-band DFB laser is modulated by a 990Mbit/s NRZ (Non Return to Zero) pattern. The signal passes through an LiNb03 circuit and is then amplified in a laser amplifier, after which the light sig­nal is detected and the transmission quality determined at a BER test station. The net gain from fibre to fibre was 12 dB. The bit error rate was < 1CT10. The results show that laser amplifiers are feasible, and complex optical systems can thus be built.

Fig. 15 Sophisticated measuring instruments are used to determine the characteristics of high-frequency optical components. Here a directly modulated laser having a bandwidth in the GHz range is being measured with a network analyzer

62

Fig. 16 The bus chip installed with connections made to low and high-speed electronic circuits. Fibres are fixed to the short ends of the chip (not shown)

The laser amplif ier amplif ies signals equally in both directions. This property may give rise to problems with external reflections, for example f rom fibre splices. There is a risk that the system wil l start to oscil late. This problem is solved by placing optical isolators in the signal path. The isolators let light through in one direct ion but block it in the other.

Summary The integrated optical circuits that can now be manufactured and, in the long view, monol i thic OEIC offer advantages over a wide range of system applica­tions. It is important that the potential of the optical medium as regards band­width should be util ized and that the number of opto-electr ical conversions should be kept at a min imum.

Fig. 17 Block diagram of Ericsson's experimental system with a bus chip and laser amplifier

References 1. Granestrand, P., Stoltz, B., Thylen, L,

Bergvall, K., Doldissen, W., Heinrich, H. and Hoffman, D.: Strictly Non-blocking 8x8 Integrated Optical Switch Matrix. Electronics Letter Vol 22(1986), pp.816-818.

2. Spanke, R.A.: Architectures fo Large Non-blocking Optical Space Switches, IEEE Journal Of Quantum Electronics, Vol QE-22 (1986), pp. 964-967.

3. Thylen, L: Integrated-optic Device for High-speed Databuses Electronic Let­ters, Vol 63, No. 2, (1986), pp. 60-80.

4. Lagerstrom, B. and Stoltz, B.: Modula­tion and Switching Using, Optical Components in Lithium Niobate. Ericsson Review 65 (1988):2, pj5.64-68.

5. Hansson, A:-K. and Pers, O.: Wave­length Division Multiplexing over Opti­cal Fibre. Ericsson Review 65(1988):2, pp. 64-68.

63

Wavelength Division Multiplexing over Optical Fibre

Anna-Karin Hansson and Olle Pers

Ericsson Telecom AB has developed equipment for simultaneous transmission of

signals from two line systems over one and the same optical fibre. The capacity

per fibre can thus be doubled on routes already in existence. The equipment

consists of standard line systems with different wavelengths and optical

components for wavelength division multiplexing of light.

The authors describe the basic principle of wavelength division multiplexing, the

components used and how they affect the multiplexed systems.

multiplexing equipment frequency division multiplexing fiber optics design engineering testing

Fig. 1, right The basic principle of wavelength division multi­plexing, WDM. Concerning S- and R-points; see text

WDM MUX DEMUX WDM coupler

Wavelength No. 1

Wavelength No. 2

Fig. 2, below Two-way 2x565 Mbit/s system with wavelength division multiplexing

LT Line terminal M Multiplexer DM Demultiplexer LR Intermediate repeater

The basic principle of wavelength division multiplexing Wavelength division mult ip lexing, WDM, gives better uti l ization of the large bandwidth of optical fibres and can in­crease the capacity of a cable network. Through WDM, signals from two or more line systems are transmitted over the same fibre. The signals, which have different wavelengths, are separated on the receive side into the original signals,

which are then detected in the ordinary way, f ig. 1. The same type of component, a WDM coupler, is used for both multi­plexing and demult ip lexing. Signals from the different line systems can be transmitted in the same or in different directions.

Application WDM can be used to increase the capac­ity of an exist ing system, particularly when all available fibres are fully uti­lized. WDM can then increase the total transmission capacity of the existing fibres wi thout the bit rate of the multi­plexed systems having to be raised. Er icssons WDM system has been de­signed for the mult ip lexing of 565 Mbit/s but it can also be used for systems with other bit rates. Line systems with dif­ferent bit rates can be mult iplexed.

The WDM couplers are completely pas­sive and contain no moving parts. Their

65

ANNA-KARIN HANSSON OLLE PERS Ericsson Telecom AB

reliability is so high that the overall sys­tem reliability is not affected. Fig.2 shows an example of a WDM system for 2x565 Mbit s. With the S and R points, in accordance with CCITT Rec. G.956, situ­ated as in f ig. 1 there will be no indica­tion in a line system that its signals are being transmitted over a fibre con­currently with those of another system. The line systems remain completely in­dependent of each other. Fault location systems, service telephones, protection switching systems etc. can be used in the normal manner. The only difference is that the S-R attenuation increases slightly since two new components have to be introduced into the signal path. Even a failure of one system does not affect the other, which will cont inue to operate as usual.

The systems The line systems used in the first WDM applications, ZAM 565-11 and ZAM 565-22, are standard systems with a bit rate of 565 Mbit/s. They were developed for the US and CEPT markets respectively. The two systems differ only as regards the mult iplexing parts. The optical parts are identical and available in two versions: for optical wavelengths of 1300nm and 1550nm respectively.

As the attenuation of an ordinary optical fibre is lower at 1550nm than at 1300nm, f ig.3a, and the transmitter out­put power and receiver sensitivity are approximately the same in the two sys­tems the repeater spacing can be made

longer for the 1550nm system. On the other hand the dispersion is consider­ably higher at 1550nm, f ig .3b, and hence this wavelength requires a laser with very small spectral width. In this case a DFB (Distributed Feed-Back) laser, which has a very narrow spec­trum, is therefore used.

There are great advantages in being able to use standard systems for WDM applications, but it also means that very stringent demands are made on the per­formance of the WDM coupler, for ex­ample as regards wavelength ranges and optical crosstalk.

Design The range of a system is specif ied in terms of permissible f ibre attenuation. The range is equivalent to the ratio of the input power in the fibre at the transmit­ter to the receiver sensitivity. ZAM 565 has a guaranteed range of 26dB at a bit error rate (BER) of 1CT9.

When WDM is introduced and the nor­mal transmitters and receivers in the wavelength division mult iplexed line systems are retained, the range of the systems will be reduced by a number of dB corresponding to the attenuation of the extra components required. More­over, some light f rom one line system may reach the detector in the other sys­tem, resulting in optical crosstalk. The receiver then requires a stronger signal in order to maintain a low bit error rate. This deterioration of receiver sensitivity

Fig. 3 Attenuation and dispersion of an optical fibre as a function of the wavelength

Fig. 4 Relationship between penalty and optical crosstalk

is called penalty and is measured in dB. Penalty also reduces the system range.

Calculations showed that it was possi­ble to reduce the range deteriorat ion to 4dB when using components already available. The WDM couplers as well as the attenuation of the extra splices and connectors must be taken into consid­eration. The range is not used to the full on most routes. Typical repeater spac-ings correspond to 1 5 - 2 0 d B fibre at­tenuation. Almost all repeater sections have a margin greater than 4dB . One of the system requirements if therefore that the range must not be reduced by more than 4 d B when WDM is intro­duced.

The system requirement must be con­verted into measurable requirements for the individual components. For the WDM coupler this means requirements for optical attenuation values between different inputs and outputs at different wavelengths. In particular the isolation, i.e. the attenuation of the non-desirable wavelength, must be sufficiently high to keep the penalty at an acceptable level.

The relationship between penalty and optical crosstalk has been measured for the receiver in ZAM 565, f ig. 4. The result shows that the penalty is very low, less than 0.2dB, as long as the disturbing signal is suppressed by 15dB or more,

but that it increases very rapidly with increasing interference. However, it is not enough to demand 15 dB isolation in the coupler; the fact that the two wave­lengths may have been attenuated to dif­ferent degrees in the fibre must also be taken into considerat ion. Differences in the output power of the two lasers and different detector responsivity at the two wavelengths may also affect the result. The overall requirement for the WDM coupler, to satisfy the most unfavour­able combinat ion of characteristics, is 26dB isolation in the 1300nm channel and 18dB in the 1550nm channel, see Technical data.

The laser wavelength can be anywhere in the bands 1290-1320nm and 1530-1570 nm respectively. Hence, the re­quirements for attenuation and isola­t ion must be met for all wavelengths in these bands. It is not possible to match WDM components with lasers in series product ion.

WDM couplers The WDM couplers in the system are used either as mult iplexers, MUX, or de­multiplexers, DEMUX. MUX has two in­puts and one output and is used to com­bine the signals. DEMUX separates the light on its single input according to its wavelength and distr ibutes it to two out­puts, f ig. 1. The isolation requirement only applies to DEMUX. As regards MUX it is more important that the attenuation is low and that the coupler does not give rise to any reflections that can be fed back and interfere with the laser.

There are two basic types of WDM cou­pler for monomode fibres: the fused and the microopt ic. Ericsson uses both, f ig.5.

The MUX component consists of two monomode fibres fused together and tapered over a length of approximately one centr imetre. The energy in the opti­cal fields in the two fibres is coupled in the fused section. This coupl ing is de-pendenton the wavelength, and by care­ful selection of the length of the coup­ling region and the distance between the f ibre cores it is possible to obtain complete coupl ing for one selected wavelength and none for another. This

66

67

Fig. 6 WDM couplers mounted on boards and installed in a separate magazine

Fig. 5 The two types of WDM coupler used

is a waveguide effect and is not found in classical optics. It has the advantage that the attenuation can be made very low; a disadvantage being that the in­sulation is high for only one wavelength, never over a band. For this reason the fused coupler cannot be used as a DEMUX.

The DEMUX is a microoptic component based on an interference filter. Such a filter transmits certain wavelengths and reflects others, but absorbs practically nothing. Graded index miniature lenses are placed between the filter and the fibres and focus the light into the fibre cores. The whole unit is glued together so that there is no air in the path of the light. The main advantage of a microop­tic WDM is its good isolation, 30dB over a wavelength band of more than 50 nm. However, the attenuation is higher than in the fused type.

The optocomponents are packaged and equipped with connection fibres. The couplers are supplied either loose or mounted on a board, in both cases with connectable fibres. Loose couplers can be installed in cable ducts, for example. Couplers on boards can be mounted ei­ther in a separate magazine, fig. 6, or in a free slot in an existing magazine. The

two fibres towards the equipment are so long that in most cases there is no need to splice in extra fibres. Superfluous fibre can be coiled and fastened to the board.

Test results The WDM couplers are designed to meet the same environmental requirements as the line equipment. Component and system tests in accordance with the re­quirements of the US National Elec­tronic Bureau of Standards, NEBS, have verified that the couplers meet these re­quirements. A field trial has also been carried out in collaboration with the Swedish Telecommunications Admin­istration. It involved two line systems ZAM 565-2, with wavelengths of 1300nm and 1550nm respectively, which with the aid of WDM couplers used the same fibre over the 35 km long test route. The trial lasted a few weeks and showed that the WDM system works well in the field. At the same time the 1550 nm line system, without WDM, was also tried over a 88 km route having an attenuation of 30.1 dB and a dispersion of 1476 ps/nm, both considerably higher than the specified requirements. The measured bit error rate of the system was 2.7x10"11.

Typical performance of WDM couplers

Fused (A) Microoptic(B) Attenuation <0.5dB 1 dB Isolation (X,±20 nm) 18 dB <30dB Reflection < - 4 0 d B varies

Summary Wavelength division mult ip lexing, WDM, is a simple means of increasing the transmission capacity of a f ibre link. WDM is particularly suitable when all fibres are in use and no systems with higher capacity are available. There are no detectable differences between sig­nals transmitted over individual fibres and those mult iplexed via WDM cou­plers over a shared fibre. The WDM cou­plers can be installed in an empty board space, in a separate magazine or in a cable duct and are connected by means of the same type of connector as normal rack cable. The only new demand made on a link in which WDM is to be intro­duced is that its guaranteed range must have a margin of 4dB , which is the total amount of attenuation added by the WDM couplers.

References 1. Johansen, B. and Stjernlof, B.:

565Mbit/s Optical Fibre Line System. Ericsson Review 62 (1985):3 pp. 130-137.

2. Hansson, A.-K. and Linden, K.: Optical Fibre Line System for 4x140Mbit/s, a New 565Mbit/s Application. Ericsson Review 64 (1987):3, pp. 102-109.

Technical data of the optical interface of the line systems Symbol rate 800Mbaud Optical signal code Scrambled bin­

ary with parity bit insertion, 16B1P

Wavelength 1300 nm Output power (before con­nector) 3-4 dBm Receiver sensitivity (BER = 10-9) =S-31dBm Loss in optoconnectors < 1 dB Wavelength 1305±15nm Spectral width (FWHM) < 5 nm

Wavelength 1550nm Output power (before con­nector) 3-4 dBm Receiver sensitivity (BER=10"9) S-31 dBm Loss in optoconnectors < 1 dB Wavelength 1550±20nm Spectral width (FWHM) < 0.25 nm Spectral width (15dB from max) < 1 nm Side mode suppression >30dB

Transmission medium Fibre Monomode,

low loss Maximum system attenua­tion S-R defined in accor­dance with CCITT G.956 26 dB Permissible dispersion at wavelengths

1285-1330 nm 140ps/nm 1530-1570nm 1400ps/nm

Mode field diameter 10±1nm External diameter of fibre 125±3nm Cut-off wavelength 1.1-1.27nm

Technical data of the WDM couplers Connector attenuation included. Max. attenuation, WDM-MUX 1.5dB Max. attenuation, WDM-DE-MUX 2.0dB Isolation WDM-DEMUX

1550 to 1300 nm channel 26 dB 1300 to 1550 nm channel 18dB

Max. penalty caused by crosstalk 0.5 dB Max. total deterioration caused by a pair of WDM cou­plers 4dB Wavelength bands 1285-1330 nm

1530-1570nm

MINI-LINK Mk l l - A New Member of the MINI-LINK Family

Per-Olof Nilsson and Staffan Reinefjord

MINI-LINK Is the collective name of a family of compact radio links designed as flexible means of extending telecommunications networks. The wider use of microwave links has led to demands for better spectrum efficiency and more extensive supervisory functions. In order to meet these requirements Ericsson has added Mk II to the MINI-LINK family. It operates in the frequency range 10-18GHz and has a transmission capacity of up to 2x8Mbits. The authors describe the differences between MINI-LINK Mk II and its predecessors, different installation possibilities and the new operation and maintenance functions and also illustrate how existing variants of MINI-LINK can be upgraded to Mk II.

radio links microwave l inks instal lat ion maintenance engineer ing

The growing demand for digital circuits - for voice, image, text and data trans­mission - has resulted in more stringent requirements as regards the quality and capacity of public networks. The main routes between large centres are rapidly being expanded by means of optical fibre cables with very high capacity. However, a chain is only as strong as its weakest link. Hence the peripheral parts of the network must also be improved or

the subscribers cannot benefit f rom the wider range of services offered. MINI-LINK is a digital radio link ideally suited for this purpose. It has the flexibil i ty and short project planning period necessary at a t ime of rapidly changing traffic re­quirements.

In a deregulatory cl imate it becomes quite usual for large users of telecom­munications to bui ld networks of their own. Such organizations lease long-dis­tance circuits but f ind it more expedient to install their own radio link routes, for example within a city, either for eco­nomical reasons or because the local te lecommunicat ions cannot provide digital circuits of satisfactory quality.

Digital microwave links are now com­mon in the networks, and users as well as frequency administrators t ighten up their demands as regards maintenance funct ions and spectrum efficiency. In order to meet these demands Ericsson Radar Electronics has added MINI-LINK Mk II to the family of microwave links.

Fig. 1 MINI-LINK Mk II for outdoor Installation has all the electronic units mounted in a weatherproof box behind the antenna

PER-OLOF NILSSON STAFFAN REINEFJORD Ericsson Radar Electronics AB

MINI-LINK Mk II MINI-LINK Mk II is a compact microwave radio for transmission of voice and data having a capacity of up to 240 PCM channels. It is available for 10,13,15 and 18 GHz. The choice of frequency band is dependent on the general regulations in the country in question, the availability of frequencies and to a certain extent also on the hop length. One hop can be up to approximately 30 km.

The technical structure of MINI-LINK and its use in the Swedish telecom­munications network has been de­scribed in previous issues of Ericsson Review.12

MINI-LINK Mk II differs from its pre­decessors in several important aspects: - It can be installed either outdoors, in­

doors or part indoors, part outdoors (split installation)

- A radio route can be looped at the far end on command from the near end

- It has higher capacity - It utilizes the frequency spectrum

more efficiently. It also contains

- a service channel - a remote supervision channel - integrated second-order multiplex.

Fig. 2 shows a simplified block diagram of MINI-LINKMkll.

Traffic capacity NINI-LINKMkll is available in five dif­ferent capacities for both the CEPT and the Bell PCM hierarchies, fig.3. The ca­pacities are 2, 4x2, 8, 8x2 and 2x8Mbit/s (CEPT) and 1.5, 4x1.5, 6, 8x1.5 and 2x6 Mbit/s (Bell). In addition, a variant for analog video with a band­width of 5 MHz has been developed. The digital transmission interfaces conform to CCITT Recommendation G.703.

Higher capacity or redundancy with au­tomatic changeover in case of failure can be arranged by having two or more radio terminals operating in parallel on a route.

Installation A radio link requires a free line of sight between thetransmitterand receiver an­tennas. This can often be achieved with the antenna mounted on a roof, without any mast, fig. 4. There are three possible installation modes: indoors, outdoors and split installation. The choice is de­pendent on the siting of the antenna and

Fig. 2 Simplified block diagram of MINI-LINK Mk II. The signal to the baseband unit can have any of the bit rates 1.5, 2, 6,8, 2x6 and 2x8 Mbit/s

Fig. 3 Variants of MINI-LINK Mk II. Frequency band, GHz

Fig. 5 Variant for indoor installation mounted in a cabi­net. All electronic units are placed indoors. Only the antenna is situated outside

the telecommunications equipment that is to be connected to MINI-LINK Mk II.

Printed board assemblies for indoor equipment are mounted in Ericssons BFD magazine. The magazine is placed in Ericsson's standardized shelves or in a cabinet, fig. 5. The equipment can also be installed in 19" racks.

Outdoor Installation Radio terminals to be installed outdoors are placed in a compact, weatherproof box, fig. 6c. Radio terminals conforming to CEPT standard are connected to the telecommunications equipment via a special cable containing two coaxial ca­bles, power feed and signalling wires.

A 60cm standard antenna is normally mounted on the equipment box. If nec­essary, it can be exchanged for an op­tional, larger antenna, which must be connected via a flexible waveguide.

Indoor installation The whole radio terminal can be in­stalled indoors. It is then connected to the antenna via a waveguide, which is the traditional method for radio links. It has the disadvantage of the maximum range being reduced because the at­tenuation of the waveguide - 1 0 to 15dB per 1 0 0 m - is added to the at­tenuation over the hop. A larger antenna can be used to compensate for the extra attenuation, but it requires greater me­chanical stability in the antenna sup­port

Indoor installation may be preferable if placing the radio terminal at the antenna makes it difficult to reach for servicing, or if it is impossible to place the radio terminal near the antenna.

Split installation With split installation the antenna and RF unit are placed outdoors, fig. 6, and

Fig. 4 The installation of MINI-LINK Mk II outdoors can be very simple

72

Fig. 6 MINI-LINK Mk II for split installation. No waveguide is required between the RF unit and the units placed indoors. The majority of the electronic units are installed indoors and thus easily ac­cessible for service

Fig. 7 Frame structure of the radio channel

J Justification bit JC Justification control bit O Remote supervision channel S Service channel

the rest of the electronic equipment in­doors. No waveguide is required be­tween the indoor and outdoor parts. A multicable is used, since communica­tion between indoor and outdoor equip­ment is on lower frequencies. With split installation the larger part of the elec­tronic equipment is easily accessible in­doors.

Operation and maintenance The prerequisites for high availability in a radio link network are that the operat­ing staff is informed immediately about service irregularities, that faults can easily be located geographically and that the maintenance system can pin­point the faulty unit or give recommend­ations as to suitable action. The core of the maintenance system of MINI-LINK Mk II is a remote supervision chan­nel for the transmission of alarms and initiation of tests etc. The channel can be connected to an existing operation and maintenance system or to a PC pro­grammed for the maintenance of MINI-LINK Mk II.

Remote supervision channel The supervision channel is extended through the whole radio link network

and occupies a time slot in the radio channel, fig. 7. The channel can be con­nected to an operation and mainte­nance centre via a leased or switched circuit in the public telecommunica­tions network. The outputs to the centre should preferably be arranged at two widely separated points in the radio link network. Such an arrangement ensures that contact with the supervision chan­nel is retained on both sides of a break, fig.8.

The interface for the remote supervision channel conforms to CCITT Re­commendation V.24 (RS-232C).

A stationary or pocket-size portable PC, fig. 9, can be connected to the radio ter­minal. A menu-driven program enables the service technician to check the al­arm status of all radio links. He can also order remote looping, switch transmit­ters on and off and carry out level and bit error rate measurements.

Alarms Alarms are indicated locally by LEDs on the various units of the radio terminal. They can also be fed via relay outputs. Two local external alarms, for example

Fig. 8

Alternative methods of extending the supervision channel

MINI-LINK Mk II

Public network Dial-up modem Service telephone Personal computer (stationary service terminal)

Portable service terminal

Traffic-carrying channel

Supervision channel

Service channel

Time division multiplex: traffic, supervision

and service telephone

burglary alarm and mast lights, can be connected to the terminal. All alarm sig­nals are also transmitted over the re­mote supervision channel, which ex­tends throughoutthe radio link network.

Fault tracing Fault location can be initiated from a hand-held terminal - and naturally from a maintenance centre, too. Faults are then pinpointed down to the unit level. A menu-driven program makes it possible to collect information concerning the operational status of the network and to initiate remote testing of any radio ter­minal in the network, fig. 9.

For most types of fault the supervision system can immediately specify where in the network the fault is located and

which unit should be replaced. If neces­sary, the service technician can use his terminal to order looping at the RF and baseband levels, or measurements of certain levels, and the bit error rate at any radio terminal in the network.

A stationary PC connected to the super­vision channel can also be used to order automatic collection of data for a statis­tical analysis of network performance.

Service channel In addition to the remote supervision channel the service technician has ac­cess to a service channel with a portable or fixed microtelephone. He can make general calls to all service telephones in use or ordinary one-to-one calls.

Fig. 9 A hand-held PC can be used to check the alarm status of all links in the network

74 Technical data Frequency 10 GHz 13 GHz 15 GHz 18 GHz Frequency stability <±1x10~4 <±1x10-'1 <±2x10- 5 <±2x10~5

Modulation 4-level FSK Effective bandwidth > 1 Hz/bit/s (99%) RF output power - without booster >13 >20 >14 >12 dBm - with booster - - >20 >19 dBm Noise figure 12 12 11 12 dB Receiver threshold, BER10-3,8Mbit/s -80 -80 -80 -81 dBm Antenna gain, 60 cm antenna 34 35 37 39 dBi Digital interface CCITT G. 703 Channel encoding scrambling and 2/4 level Gray conversion Looping facilities RF, baseband composite and baseband tributaries Feeding voltage 24 or 48 V DC Power consumption 24 35 27 21 W Environmental endurance - outdoor equipment

temperature -40to+55°C humidity < 100%

- indoor equipment temperature 0 to+45°C humidity < 95%

The service channel is an asynchronous 64kbit/s bus with facil it ies for E&M sig­nall ing. It is mult iplexed with the traffic and supervision channels in the radio channel. The interface is of the balanced four-wire type in accordance with CCITT Recommendations G.712, G.711, and also includes E and M terminals for the detection and generation of calls.

Compatibility Customers using the earlier version of MINI-LINK can upgrade their systems to MkII . Electrically and mechanically the units in Mk l l are fully compatible with the earlier MINI-LINK. The upgrade con­

sists in changing one or two printed board assemblies and possibly adding a MUX board. In the case of indoor or split installation a new magazine is also re­quired.

Summary Microwave links constitute a flexible transmission medium which facilitates rapid extension and reconfiguration of public and private networks. MINI-LINK Mk II is a new version of MINI-LINK which provides more options as regards installation mode and maintenance funct ions. It also meets very stringent requirements for frequency efficiency.

Dimensions and weight Frequency 10 GHz 13 GHz 15 GHz 18 GHz Dimensions, mm (HxBxD) - outdoor installation,

including antenna 670x623x679 - indoor installation,

including cabinet 375x603x346 - split installation

antenna unit 623x623x527 RF module 420x350x200 420x350x200 indoor unit,

including cabinet 375x603x346 375x603x346

Weight, kg - outdoor installation,

including antenna 19 20 25 26 - indoor installation,

including cabinet 28 29 - split installation

antenna unit 11.3 11.3 11.3 RF module 10 9 10 indoor unit, including cabinet 25 25 25

References 1. Bergman, S. and Johnsson, K.-A.:

MINI-LINK 15. Ericsson Review 59 (1982):2, pp. 76-81 .

2. Norremark, J., Skyttermark, B. and Wallgren, R.: MINI-LINK in theSwedish Network. Ericsson Review62(1985):2, pp. 42-51 .

Solar and Wind Power — Experience Gained in Argentina Lars Ejdling

Installing radio stations in inaccessible or remote places often involves great problems. In particular the power supply requires careful investigation. Conventional power supply equipment, for example diesel generators, have the disadvantage of requiring fuel refills. If solar cells or wind generators are to be used it is necessary to make a detailed on-site study of the number of sunshine hours and the variations in wind-force Moreover, solar cells require large battery reserves so that operation can be maintained in sunless and calm conditions. The author describes how Ericson's system ERIGEN. which uses three power sources - the sun. wind and a mini-diesel power plant - has solved the power supply problems for a radio relay link station situated on a mountain peak 4.300m above sea level.

LARS EJDLING CAT, Argentina

power stations solar power stations radio stat ions maintenance engineer ing telecontrol

Fig. 1 The picture illustrates normal weather conditions at the radio relay station with clouds below the peak. The wind turbine is being erected. The building behind the mast provides accommoda­tion 'or staff temporarily working at the station

Compahia Argentina de Telefonos S.A. is in charge of a large area in Argentina and responsible for approximately 10% of telephone services in the country. The company serves 350,000 subscrib­ers, and the total number of telephone sets amounts to 340,000. The automa­tization factor is 96.2%. All telephone exchanges owned by the company, both electromechanical and electronic, have been supplied by Ericsson,

The topography of the company's terri­tory varies from desert to mountains

with interjacent valleys where farming or forestry is practised. Different meth­ods are needed to maintain the links be­tween population centres in the compa­ny's territory. In this article is described how an obstacle consisting of a moun­tain range with a height of 4,700 m above sea level is bridged.

Geographical conditions The north-western part of the country contains mountain ranges which be­come successively higher until they reach the Andes, whose peaks are more than 6,000 m above sea level. The slopes up towards the Andes contain inhabited valleys with population centres, someof considerable size, which are tourist at­tractions or have mineral deposits. Other places have special climatic con­ditions favourable to viniculture and, hence, considerable wine production.

76

Technical data for the radio equipment Radio relay link terminals

NL125 2 Frecuency band 7,125-7,425 MHz RF power 30 dBm Configuration 1 + 1

"hot stand-by" Baseband 300 channels

60-1364 kHz Power consumption 130 W

Radio relay link terminal 2TM 120/900 1

Frecuency band 790-960 MHz RF power >5 W Configuration 1 + 1

"hot stand-by" Baseband 120 channels

0,3-600 kHz Power consumption 120 W

A radio link station, whose power supply system is described below, is situated at Valles Calchaquies, a pre-Columbian In­dian site comprising several valleys be­tween the 4,700m high mountain ranges Quilmes and Cumbres Calchaquies. The latter separates Valles Calchaquies from San Miguel de Tucuman, capital of the Tucuman province.

Studies of the possible ways of con­necting the telephone network in these valleys with the network in the provincial capital indicated that the best solution would be to put an active relay station on the peak El Negrito, 4,330 m above sea level. The station was named after the peak.

Radio equipment Right from the start the station was plan­ned with consideration paid to expected future expansion and to what places could be reached by radio realy link from the chosen site. The choice of ra­dio equipment was based on previous experience and made with the objective that it should provide maximum safety during installation, operation and main­tenance.

Aerial system The climate is such that ice formation had to be considered in the calculations for the aerial mast. The surface of the large antennas are made of wire netting in order to reduce the wind load.

Technical data of the antenna Stayed mast. Lattice with triangular cross-sec­tion, sides 110 cm wide, ladder inside

Height 15 m Load assumptions

Wind speed 27,5 m/s Ice formation 6 mm

Antenna data in calculations at a height of 12 m Parabolic antenna with

smooth surface, 2.4 m di­ameter Parabolic antenna with smooth surface, 1.2 m diameter

at a height of 9m Parabolic antenna made of wire netting, 4 m diameter

at a height of 5 m Parabolic antenna made of wire netting, 4 m diameter

at a height of 4 m Dipole with corner reflector

Power supply The company did not have any previous experience of the powering of remote sites and based its choice of power sup­ply system on the following require­ments and conditions: - The power supply should be uninter­

ruptible - Equipment should be easy to trans­

port and install - Only minimum maintenance should

be required - The available meteorological data

was meagre.

It was clear that a system based on the use of renewable power sources, i.e. the sun or wind, had to be used, but avail­able meteorological data was not suffi­cient for determining whether a system with only a wind generator or only solar

Month Temperature (°c) Wind speed (m/s) max.abs. min.abs mean max. mean min, mean

Jan 14 -2,7 2,31 8,50 Feb 12 -4,1 1,42 5,40 March 16,8 -2,3 1,17 4,38 0,15 APf i ! 8,1 - 8 4,18 10.86 0,76 May 7,1 -7,9 1,53 6,00 0,03 June 7,8 -12,2 3,89 11,09 0,18 July 3,8 -13 2.85 9,50 0,30 Aug 7.8 -12 1,24 5,61 Sept 12,3 -12,6 4,01 11,45 0,56 Oct 15,3 -8,1 1,90 6.60 Nov 16 -3,9 2,90 8,92 0,26 Dec 14 -6,0 1,81 6,39 0,10

Summer 1,81 6,63 0,09 Winter 2,89 9,09 0,31

Table 1 Measured meteorological data

Sunshine hours: the number of days during the year without any sunshine is approximately 32

77

Technical data of power supply system Solar panels

Type M-51 52 st Power 420 W Voltage 48 V

Diesel generator Power 3 kW Voltage 48 V

Wind turbine, vertical axis, Darreius type with three blades, Savenius rotor

Max. power 950 W Blade length 3 m

Battery Capacity 2x770 Ah Reserve time: 7 days

panels would be feasible. The lack of "exact" meteorological data would have resulted in overdimensioning of the battery and solar panels or wind generator.

The meteorological data that was avail­able and could be considered fairly rep­resentative had been collected at a place 4,150 m above sea level, situated approximately 3 km from the chosen site and in different terrain, table 1. It was a reasonable conclusion that the actual wind-force would be better than the measured values. However, the only possible way of obtaining sufficient me­teorological data -detailed enough to justify the choice of one single type of power source - would have been to camp at the chosen site and collect data for at least a year.

The company chose a combined sun/ wind system with an Ericsson ERIGEN

mini-diesel generator as a standby, which had several advantages: - The delay that recording of mete­

orological data would cause was avoided

- The combined sun/wind system is smaller than a system with only one power source would have been

- The battery could be made smaller since the need for standby power is reduced when the system has three power sources

Remote data In addition to the power sources. ERIGEN includes a computer that con­trols all system functions so that max­imum use can be made of the solar and wind energy, fig. 2. The computer also controls transmission of data in both di­rections between the relay station and the terminal station where the mainte­nance staff can be reached. At the relay

Fig. 2 Diagram showing the function blocks in ERIGEN and the connection of the system

78

station, meteorological data and data from the different power sources is col­lected and transmitted. Control data is received from the terminal station and distributed to the respective power sources by the computer. The data/con­trol signals transmitted by ERIGEN are described in the box "Measured quan­tities...".

Accommodation of equipment Temperatures below zero reduce bat­tery capacity and also the starting ability of the diesel engine, but heating the power supply equipment room would require more energy than the amount used by the radio equipment. In order to achieve a suitable temperature without any heating devices the equipment was installed in a buried container. The soil levels out the temperature variations that occur above ground. This fact was exploited to the full by designing the container with thin walls, 8 mm, made of glass fibre reinforced plastic. Heat can then be transferred in both directions, and the internal heat, dissipated from both the radio equipment and the diesel generator, is conducted out into the soil. For easier transport the container was constructed of panels, 0.8 m wide and of different lengths, which were as­

sembled on site. The joints were sealed with silicon.

Premises for a staff of five people were built on the ground using conventional building materials.

Installation In Argentina there is very limited avail­ability of large helicopters that can fly to such heights as the radio relay station site. There is certainly no such helicop­ter stationed in the relevant part of the country, so no helicopter assistance could be expected for the installation. It would have been even more hazardous to base the opportunities for fault cor­rection and maintenance on the avail­ability of helicopters.

Helicopter assistance must always be booked at least two months in advance, and even then it might not be forthcom­ing if the helicopter was needed for some other urgent task. Under these cir­cumstances mules were chosen for the transports to the station.

The starting point for the last climb up to the station is situated at 3,000m above sea level and can be reached comforta­bly by a road that is trafficable all the year round. From there it takes 3 1/2-4 hours to reach the peak by an accept­able footpath.

Fig. 3 A part of the radio relay station with the solar panels in the foreground

79

Fig. 5 Living quarters for staff temporarily working at the station

Installation was divided into the follow­ing stages: - Construction of a building for installa­

tion personnel - Erection of masts and assembly of so­

lar panels - Assembly of antennas and radio

equipment - Assembly of wind turbine.

Installation times were normal apart from the expected extra time necessi­tated by the mode of transport and the inconveniences caused by the altitude of the site.

The wind turbine was installed after the station had been put into operation sin­ce it was delivered later than the rest of the equipment. As a result the turbine had to be mounted on a separate, small­er mast, because with the antennas al­ready in position it was not possible to lift the turbine to its intended place.

Maintenance Only one fault has occurred since the relay station was taken into service. It occurred on October 1, 1986, after more than two years of operation, and caused an outage of the signalling system of the station which lasted for five hours and 35 minutes. The fault occurred in the microprocessor board in the control

equipment, which stopped charging the battery.

The remote supervision immediately alerted the maintenance staff to the fault. The battery reserve time is seven days and the fault clearing visit could thus be planned in advance. There was no interruption in the radio system, and it returned to normal operation when the fault had been cleared. Since then there have been no operational disturbances.

The number of visits for preventive maintenance has been reduced to a minimum: visits required to check lubri­cation, battery density, the cleanliness of the solar panels etc. At the same time the serviceman carries out the stipul­ated maintenance routines for the radio equipment.

Conclusions The feasibility of installing an active re­lay station at a remote site was analysed and compared with the possibility of using passive reflectors, at the same or another site. Particular attention was paid to the differences as regards main­tenance. An assessment was made of the economical and technical prere­quisites, and the final conclusion was that the chosen alternative was prefer­able. An active relay station has the add-

Fig.4 View of the radio relay station with the wind turbine in the foreground. The ventilation tubes for the power supply unit and the entrance to the container can be seen in the background

Box Measured quantities, alarms and other signals communicated by ERIGEN

Meteorological data Wind speed

instantaneous mean value for 30 seconds mean value for 6 hours

Wind direction instantaneous mean value for 6 hours

Temperature five points indoors and outdoors

Relative humidity

Wind power data Current

Power, mean value per 6-hour period Alarm signals for

processor faults regulator failure generator overload low output voltage

Diesel generator data Current Power, mean value per 6-hour period Operating time Indication of equipment being in operation Remote start/stop Failure alarm

Solar panel data Current Power, mean value per 6-hour period Failure alarm

Battery data Voltage Capacity, Ah

Load data Power, mean value per 6-hour period

Other alarm signals Overvoltage Undervoltage

ed advantage of providing several func­tions that are not available with a pas­sive reflector.

From the chosen site, the coverage east­wards - the region which is most dense­ly populated - encompasses an area of plains with a clear line of sight for over 150 km throughout an angle of more than 90°.

The company knew from previous expe­rience that the radio equipment had high reliability, so the only problem was to find a reliable and uninterruptible power source. The problems of running some type of conventional power supply to places difficult of access make sun/ wind systems the natural choice in such cases. The amount of energy obtained from the sund and wind varies greatly with time and also in a random manner, but normally the two power sources supplement each other well in the long run.

The station was taken into service on July 15, 1984, and has been operating for three years. On the part of Compahia Argentina de Telefonos S.A. the choice of ERIGEN from Ericsson's Power Divi­sion has been entirely justified both as regards operation and reliability. Once the good performance of the system had been verified, decisions were made to extend the relay station with digital links to other localities. As plans were made for these projects the company started to collect meteorological data. The sta­tion is now transmitting weather data automatically, from appropriately lo­cated transducers to the manned termi­nal station. It will thus be possible to calculate how much energy can be ob­tained from the sun and wind and to what extent the mini-diesel will have to be used. This knowledge will be ex­ploited for subsequent expansion.

References 1. Aker lund, J.: ERICSSON SUNWIND

Ericsson Review 59 (1982):1, p p . 4 0 -47.

2. Ottosson, J.: ERIGEN Data Logger for the Supervision of Solar and Wind Systems and the Collection of Mete­orological Data. Ericsson Review 64 (1987):3, pp. 110 -115 .

80

Fig. 6 Measurements at the control rack of the ERIGEN system

ERICSSON

ISSN 0014-0171 Telefonaktiebolaget LM Ericsson Liungforetagen. Orebro 18