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ERICSSON REVIEVol. XXXIX No. 3 962RESPONSIBLE PUBLISHER: HUGO LINDBERGEDITOR: SIGVARD EKLUND, DHSEDITOR'S OFFICE: STOCKHOLM 32SUBSCRIPTIONS: ONE YEAR $ 1.50; ONE COPY $ 0.50CONTENTSAn Experimental Data TransmissionSystempage62Crossbar P.A.B.X. ARD 561Duration Meter VMF 81L M Ericsson News fromQuarters of the WorldAll728085On cover: Operator's console forL M Ericsson's P.A.B.X. ARD 561COPYRIGHT TELEFONAKTIEBOLAGET LM ERICSSON PRINTED IN SWEDEN, ESSELTE AB, STOCKHOLM 1962

An Experimental Data Transmission SystemWWIDL, T E L E F O N A K T I E B O L A G E T LM ERICSSON, STOCKHOLMUDC 621.394.1LME 81During the last few years technical development has entailed an everincreasingdemand for the transmission of vast amounts of data betweengeographically separated centres. Particularly military defence systems are inurgent need of data transmission equipment permitting higher speeds. It istherefore natural that the system described below should have been developedto the order of Kungliga Flygforvaltningen (the Royal Swedish Air ForceAdministration), which also drew up the required basic specification. Thisresulted in the construction of a phase-shift data transmission system permittingthe transmission of binary digits at a speed of up to 1500 bauds overtelephone circuits.In the following chapters a description will be given of the function andconstruction of the system. In conclusion a few test results are given.621. General Information on Data TransmissionThe fields of application for data transmission systems are manifold, andmay be illustrated by means of the following two simple examples.To simplify the replenishment of supplies, each branch of a multiplefirm sends a list of required goods to the main office every evening. Thedata transmission system applied for this purpose is only used for a shortlength of time, but for the transmission of a large amount of information.The transmission may for instance be carried out over a switched telephoneconnection.The traffic on a railway line is controlled by data regarding trainmovements, switch positions, etc. In this case the data transmission systemoperates continuously. Its great transmission capacity is necessary to keepthe traffic supervisor informed about the situation. By its nature the systemrequires a leased telephone connection.As the examples show, a data transmission system always co-operates withdata-handling equipment in some way.A complete system, comprising data-handling equipment, control and checkingcircuits, receiving and transmitting devices as well as data transmissionsystems, is called an integrated data system. Obviously it will be profitableto standardize the inputs and outputs of the data transmission system as wellas their operating principles to make it possible to use them in various integrateddata systems. Proposals for a solution of these standardization problemsarc under discussion in the CCITT Special Study Group A. Thus theequivalence has been declared between:Binary digit 1 = "Mark" = positive current in the case of bipolar signals == condition ZBinary digit 0 = "Space" = negative current in the case of bipolar signals == condition AAn effective data transmission system should meet the following requirements:high speedlow vulnerability to noise and pulse interferenceslow vulnerability to distortion in the transmission pathconcentrated signal spectrum on the linesimple as well as economic terminal compositionWhen designing a system the above factors will give rise to a series ofcompromises closely related to the transmission line employed. From aneconomic point ot view it is advantageous to use for data transmission those

Fig. 1Pulse shapingX8366Fi(t) — Pulse shape> Incoming signalSi(f) — Amplitude spectrumFB(t) — Pulse shape 1 Signal after pulseS..(f) — Amplitude spectrum I shapingT^ — Bit period•h Bit frequency-Tb 0 Tb0 05fbtelephone and telegraph networks which already exist. When these networkswere designed, however, in most cases no regard was paid to the specialrequirements as to the phase and attenuation conditions of the network fordata transmission. The line distortion will limit the transmission speed of thesystem and its resistance to interferences. Consequently, if data are transmittedover leased telephone circuits, it is advantageous to compensate for thedistortion by means of equalizing networks. This is not possible in the case ofswitched telephone connections, because apparently it is not economic toequalize all types of telephone circuits in one network.In that case it is essential to choose the appropriate modulation and detectionmethods to obtain compensation for the decrease of the circuit quality.Fig. 2Data transmission system, senderFp— Pulse-shaping filterFi — Intermediate-frequency filterF2 — Low-pass filterG, — LC-Oscillator (7.4 ke/s)G: — LC-Oscillator (9.1 kc/s)R. Rv — Frequency dividerGj< — Quartz crystal oscillator (96 kc/s)Ai — Output amplifierDS — PadKl — Clock-pulse generatorMi, Mo — Modulator2. Basic SystemWhen designing the data transmission system developed by L M Ericsson,special attention was given to the desirability of having a concentrated signalspectrum on the line in order to reduce the need for equalization as much aspossible. This has resulted in a system which uses phase-shift modulationtogether with special pulse shaping at the sending end and synchronousdemodulation and pulse regeneration at the receiving end. With the aid offigures 2 and 4, a detailed description will be given of the function of thesystem at a transmission rate of 1500 bauds. For the sake of simplicity theinternal group delays of the system have been ignored in these figures.Block diagram for transmitterClock pulses Bipolarfb = 1500 c/s data signalWaveforms of data signalFrequency spectra of data signalt[ms]0 1.5 3 4 5 6 7 5 9ht [kc/s]nPhase-shifldata signalraJ * .0 63

Saving band width by pulse shapingIn the transmission of information a data flow in the form of a bipolarsignal is fed to the sending terminal of the data transmission equipment.An incoming "1" (E) is for instance represented by a positive square wavecurrent pulse and a "0" (N) by a negative square wave current pulse. Thedata flow can be considered as consisting of a series of positive and negativepulse elements or bits. To obtain an idea of the pulse shaping a single positivesquare wave is studied (fig. 1). The pulse contains a wide pulse-frequencyspectrum, which is limited and shaped in a pulse-shaping filter with a cut-offfrequency corresponding to half the bit frequency (the bit frequency /,, denotesthe reciprocal of the bit period, /,, (c/s) = 1/T,, (sec. 1 ).Thus, at a data speed of 1500 bits/second the spectrum is concentrated toabout 800 c/s bandwidth (baseband). In passing through the low-pass filterthe square wave is converted into a pulse whose form can be represented assin x/x, showing a peak at the middle of the pulse and zero crossings at intervalsequivalent to multiples of the bit period as measured from the middleof the pulse. If in a message bits are transmitted at a speed of /,,. thesin x/.v-pulses will likewise occur at intervals equivalent to multiples of the bitperiod i 6 .Therefore, we may state that every pulse peak coincides with the zerocrossings of the adjacent pulses. When the filtered pulse elements are scannedin the middle of the bit. amplitude values will be obtained which are independentof the polarity of the adjacent bits.Modulation at the sending endAfter pulse shaping in filter F p (fig. 2) the signals will cover a frequencyband of 0-800 c/s, a band which owing to its position is unsuitable for transmissionover telephone channels. By means of a balanced modulator M, anda first carrier frequency, a double-sideband signal is generated which coversa frequency band of 6.6-8.2 kc/s. Fig. 3 shows the circuit diagram of themodulator. In step with the carrier frequency either circuit A^D^-D 2 or circuit/4 X -D 4 -D 3 is closed. Thus, either path A 1 -D 1 -A 2 or path A^-D^-A., is openedfor the data signal. After modulation the intermediate-frequency band signalhas an envelope which is equal to the baseband wave form at the modulatorinput, and a carrier phase depending on the polarity of the baseband signal.A change of the signal polarity in the baseband will produce a 180 phaseshift in the carrier in the intermediate-frequency band. This is why this typeof modulation is termed "phase-shift modulation".The modulated signal passes through an intermediate-frequency filter, whicheliminates higher modulation products. In a further modulation stage—comprisingmodulator M 2 and oscillator C•.—a second carrier frequency is addedwhich translates the data signal to the line band, the envelope and phase relationsremaining unchanged. After filtration and amplification the data signalsare transmitted over the line. The line frequency band used for this purposeis about 1600 c/s, so that the present data transmission system requires fortransmission a frequency band which is only slightly higher than the bitfrequency.Demodulation at the receiving endOn their way to the receiver the data signals are exposed to line distortionsand interferences. At the receiver input a high-pass filter eliminates l.f. pulseinterferences, e.g. interference from d.c. signalling on adjacent telephone wires.The correct receiving level is ensured by means of a regulating amplifier,which stabilizes the signal level. A subsequent limiter reduces the disturbingeffect of transient pulses which exceed a certain voltage threshold. Fig. 4shows a distortionless received signal which is modulated in modulator M :1with carrier frequency f./. The subsequent intermediate-frequency filtermatches the width of the signal spectrum and attenuates interference

Block diagram for receiverWaveforms of data signalDS F-t[ms]Fig. 4 X 836Data transmission system, receiverDS — PadF3 — High-pass filterAa — Regulation amplifierB — LimiterM3,Mi — ModulatorG. — LC-Oscillator (9.1 kc/s)F^ — Intermediate-frequency filter (6.6—8.2 kc/s)DL — Full-wave rectifierF4 — Band-pass filter (14.7—14.9 kc/s)R, Rv—Frequency dividerD y — Delay circuitF, — Low-pas, filter (1.1 kc/s)G^ — Quartz crystal oscillator (96 kc/s)L — Logic circuitN — Zero-crossing detectorA3 — Limiter amplifierDet— Amplitude detectorP — Pulse regeneratorReg— Carrier regeneratorkl — Clock-pulse regeneratorFig. 5AccelerationperiodClock-pulse generatorI SF-0-~ s n ;'mrpF• Clock—r—r—1 pulsesI^L.EIil outputJRetardationperiodG^ — Quartz crystal oscillatorRv — Frequency dividerd — Pulse differentiation circuitLi, Lj, h, — And-circuitL, — Or-circuitFa, Fd— Flip-flopIV — Zero-crossing detectorR Frequency divider (Binary counter)Clock-pulsesfb = 1500 c/sBipolardata signaloccurring outside the signal band. Owing to frequency differences betweenf 2 and f 2 ' as well as the effect of frequency drift in the transmissionof signals over carrier channels it is not possible to demodulatethe signal in the intermediate-frequency band with a fixed carrier frequency//. On the other hand, the signal contains a spectral component which permitsregeneration of the carrier frequency necessary for synchronous demodulation.By full-wave rectification and selection of the double carrier frequency 2/,'in a narrow band-pass filter an exact reference frequency, independent ofdata, is obtained. After a frequency divider and a delay circuit the correctcarrier frequency is obtained, occurring in two possible phase positions, Aor B, having a phase shift of 180°. If a distortionless signal is demodulatedin modulator M, by means of carrier frequency /,' in phase position A,a data signal which is equal to the sender baseband signal after pulse shapingwill be obtained after filtration. If, on the other hand, the demodulationis carried out in phase position B, the polarity of the regenerated signal willbe changed, resulting in a transmitted "1" being perceived as a "0", andvice versa. (The signals are inverted). In chapter 3 a description will begiven of two possible means of eliminating ambiguity in transmission.Regeneration of the d. c. signalIf, after demodulation and amplification in the limiter amplifier, the datasignal is scanned in the middle of each bit, the information contained inthe signal element is obtained from the polarity of the amplitude. Therefore,it is essential to regenerate the bit frequency in the first place.If the data flow ensures a certain number of polarity changes per numberof transmitted bits, the zero crossings can synchronize a clock-pulse generatorthat generates the bit frequency. Fig. 5 shows the operating principle of aquartz crystal controlled clock-pulse generator. A quartz crystal oscillatorG k (96 kc/s) drives a 32-step ring counter via a frequency divider R, andlogic circuits L, and L 2 . A clock-pulse f-, is produced after every cycle ofthe ring counter. Flip-flop (toggle) F a is driven from counter R and is in the"acceleration condition" during the time f : to f 16 and in the "retardationcondition" during the time f 17 to f 32 - If a zero crossing occurs under theacceleration condition the synchronizing pulse is led from the zero-crossing65

detector JV over logic circuits L :t and L., direct to the input of the ring counter.The revolution period of the counter is diminished by l /s2 during one cycle.During the retardation period a synchronizing pulse will block the path viaflip-flop F A , differentiation circuit d and logic circuit L, for one of the pulsesproceeding from the quartz oscillator. Thus the revolution period of thering counter is increased by "32 during one cycle. If no zero crossings occurthe revolution period of the counter will not change. In the detector everybit is scanned in the middle by means of the regenerated bit frequency. Arepeating flip-flop will reproduce the data signal in the form of square waves.3. Use of the SystemAs was mentioned in the preceding pages, a data transmission terminalis connected to a transmission system as well as to a data-handling equipment.In order to facilitate the matching of the data signals to the lines their spectracan be shifted by changing the oscillators G L , of the data transmission terminals.A line connection over a loaded cable, for instance, requires a signal spectrumshift to 0.5—2.1 kc/s. This is obtained when /., = 8.7 kc/s. The flexibility inrelation to the data-handling equipment is increased by the possibility ofaltering the bit frequency by means of frequency divider R,. which is variablein steps. To achieve the best possible pulse shaping and interference elimination,the pulse-shaping filter of the sender and the intermediate-frequency filterof the receiver have to be changed when the bit frequency is changed.System using differential codingData transmission systems using differential coding are particularly suitablefor continuous transmission between data-handling equipment providedwith buffer stores.In order to eliminate ambiguity in demodulation a differential codingequipment is inserted between the data-handling equipment and the datatransmission equipment. At the sending end a "0"-voltage at the input ofthe encoder will result in a polarity change in the middle of the bit at theencoder output, whereas a "1 "-voltage will not affect the output voltage ofthe encoder (see fig. 6).With the aid of an external or internal bit-frequency clock-pulse generatora data flow (0, 1) is read out from the data-handling equipment and fedto the encoder, which in its turn produces a data signal (N. E). The outputsignals of the encoder will pass through the data transmission equipmentoutlined in figs. 2 and 4 and. when demodulated in phase position A, willPDBSKoDatasignalClockpulsesDifferential- coding data --un^^^F-Fig. 6Data transmission system usingcodingDBS — Data-handling senderQBM — Data-handling receiverP — Pulse regenerationKo — EncoderDe — DecoderKl — Clock-pulse regenerationKle — External or internal clock-pu se generationDTS — Data transmission senderDTM — Data transmission receiver66X 8368differentialKL 2 DTSKl\Distortion^linetOTM3 De'DBMssDifferentialcoding datasignalClockpulsesDatasignalI E 1 N3E3E3Phase position B 1J__^^^tHzFtftr'pB

esult in signal P A , whereas when demodulated in phase position B a signalPn will be produced. If two pulse elements of different polarity occur insuccession at the input of the receiver decoder a "0"-voltage will be generatedat the output during one bit period.Two pulse elements of the same polarity will produce a "1 "-voltage atthe output. Consequently, the output signal of the decoder is independent ofwhether the modulation is carried out in phase position A or B and correspondswith the input signal of the encoder at the sending end. In step with theregenerated bit frequency the bipolar data signal is fed to the data-handlingterminal at the receiving end.67

System using start codeIn certain data transmission systems, every data message is preceded by astart code consisting of a character combination (in its normal or invertedform) which does not occur in the subsequent message. The start code cantherefore be used at the receiving end for ascertaining whether the modulationhas been carried out in phase position A or B. When position B is useda change-over switch in the data-handling receiver or a phase shifter in thedata transmission receiver will invert the message which follows a start codeand will thus eliminate ambiguity in reception.4. The Mechanical Construction of the SystemEquipment constructionThe design of the mechanical equipment for this data transmission systemfollows the new L M Ericsson construction principles for transmissionequipment, involving the use of miniature components in connection withthe adoption of transistor and printed-wiring techniques.The sender functions are distributed among 12 units and those of thereceiver among 17 units. Each unit contains one function, such as a filter,modulator or amplifier. To facilitate maintenance the most important unitshave been provided with test points for fault location at the front of theunit. The adjustment of bit speed, signal centre frequency and level iseffected by means of links at the front sides of the units.The power supply for the sender and the receiver is obtained from an individualor a common mains supply unit. The alarm equipment indicatesfailure of the power supply and at the receiving end also the occurrence offaulty signal levels.Shelf and bay constructionThe units are mounted in a shelf construction developed for 19" wide bays.Each shelf is designed for 12 units. A horizontal connecting strip on theshelf comprises connecting links, pads, maintenance measuring points andfuses. A panel on the right-hand side of the shelf is designed for the baycabling. The units are protected by dust covers. The horizontal connectingstrip, however, is directly accessible. The data transmission sender occupiesone shelf (fig. 7), whereas the data transmission receiver occupies 2 shelves(fig. 8).5. Technical DataMiscellaneousModulation speeds /,,Signal centreLinerequirementsfrequenciesbandwidth requiredCode requirementsfor synchronizing the clockpulse generator of the receiver1 000 bauds1 500 bauds1 100 c/s1 300 c/s1 500 c/s1 700 c/s1 900 c/sswitched or leased telephone lines withmaximum frequency drift ± 10 c/s1 600 c/sat least one 0-elementper 75 1-elements

Tolerance to line interruptionThe bit frequency regenerationpermits breaks of approx.Stability requirementof external clock-pulsegeneratorAmbienttemperature1 000 (ms)±2- 10-i-f,, (c/s)0—45° CSenderLine sideData handling sidedata signal andexternal clock-pulseOutput impedanceOutput levelInput impedanceInput voltage600 ohms+ 6 dbm max.— 30 dbm min.3 000 ohms± 6 VReceiverLine sideData handling sidedata signal andregenerated clock-pulsePower supplyPower consumption, senderreceiver6. System TestsInput impedanceInput levelOutput impedanceOutput voltage across1 kilohm load+ 12 V3 W4 W600 ohms0 dbm max.— 30 dbm min.< 250 ohms±6 V— 12 V4 W8 WMost of the errors occurring in data transmission over telephone circuitsare caused by pulse interference and transient interruptions. Not even a datatransmission system of optimum design can prevent errors occurring in the eventof interruption. If the system is given appropriate dimensions, however, goodresistance to certain types of pulse interference may be obtained. Theresistance to interference is reduced by group delay and attenuation distortionin the transmission path and is raised when the signal frequency band isfiltered, owing to the limitation of the disturbing amplitude. In order togive the system parameters optimum design and to measure the deteriorationof the transmission channel on account of phase and attenuation distortionit is advantageous to test the system by means of a reproducible type ofinterference, e.g. a number of tape recordings of typical disturbing pulses. ItDataData test transequipmentI missionequipmentNoise test circuitITestobject11Fig. 9 X 8369Test circuit for data transmission systemsDCS — Data test senderDCM— Data test receiverFA — Error analyzerDJS — Data transmission senderDTM — Data transmission receiverDSHYpWLBG— Pad— Hybrid circuitBand-pass filter, bandwidth JI (c/s)Output power meter ImW)— Line— Noise generatorBG - %DSI*

is also possible to use white noise as interference. In this case it is assumedthat a system with good resistance to white noise will retain this property inthe event of pulse interferences.The system tests referred to here were carried out with a test circuit whichpermits the injection of white noise at a certain signal-to-noise ratio at the inputof the data transmission receiver. The test circuit employed is shown in fig. 9.A data test sender generates a data flow which in the data transmissionsender is converted into phase-shift data signals. The signals pass through thetest object, e.g. a loaded cable, which is connected via two transformers.White noise is added to the signals in a hybrid transformer circuit. A band-passfilter, whose passband is wider than the signal spectrum, limits the noise signalto an effective bandwidth of J /. After being disturbed by the noise, the signalis demodulated in the data transmission receiver and fed to the test receiver.In the test receiver the incoming messages are compared with a programmedreplica of the information sent out from the data test transmitter. An erroranalyzer will count both the number of incoming bits and the number oferroneous bits; in this way the error probability p,. is determined.number of bits in errornumber of received bitsFig. 10 aData transmission over loaded cableError probability pc with noise interference Rmr_X8370pt — Theoretical error curve for differentialcoding phase-shift systemp — Test object, free from distortion and interferenceError curves for 10, 15. 20 loaded cablesectionsFig. 10 bAttenuation A and group delaycableX8371of loadedBy means of an output power measuring instrument both the signal power(noise switched off) and the noise power (signal switched off) are measured,resulting in the signal-to-noise ratio R at the filter output. For a comparisonof theoretical and practical results a fictitious filter bandwidth, assumed asequal to /,,, is often used as a reference. The resultant normalized signal-to-noiseratio is /?,„,..average signal powerR = 10 log - - ; R„average noise powerR10 log—-(db)7 bThe curves in fig. 10a show error probability p, as a function of the normalizedsignal-to-noise ratio R lllr . Curve p, represents the theoretical valuemeasured for the data system, assuming the occurrence of a random dataflow ("random" refers to the unpredictable sequence in which "l's" and"0's" are sent out). Curve p 0 is obtained with the aid of the above-mentioned[db] HSignal widthat 1500 bits/sec.30-?n^i////////// ,/////T 20T 15/T 10A 2010A,5^^^"^A 102.5"•Frequency70

\Error probabilityPe'10A[db]Signal widthat 1500 bits/sec.in75-t32-•6//\ ( \ i\ i > '\ 1T 3\ \\ \\ \ \ \\ VA\0.5-0.4-0.3-02-0.1\ \\\ \ \\ \ \\\Po\\\\\PSF\ \\ \N \\ \ \ \ \N / ^ 2T l- - > — - - 'T BFP1P2P3A3nns2 Rmr[db]Signal-tonoise-ratio-^ —-—"'A2A,ABFIf [kc/s]FrequencyFig. 11a x 8;Data transmission over carrier circuitsError probability pe with noise interferencePuPBF';!Fig. 11 bRmrTest object, free from distortion and interferenceError curves for 2 carrier systems connectedin tandem- Error curves for carrier circuit with differentphase equalizersX8373Attenuation A and group delay T for carriercircuit with different equalizersnoise test circuit, if the test object is free from distortion and interference. Theinformation used in the test will imitate a random data flow.The register of the data test sender may for instance be programmed witha random binary-digit sequence. When sending, the register is subjected to acyclic read-out procedure; the test sender will generate a quasi-random dataflow.To demonstrate the influence exterted by line distortions a further diagramhas been given of the error curves that were obtained when the test object offig. 4 consisted of a loaded cable with attenuation and group delay values asshown in fig. 10b. The test was carried out over 10, 15 and 20 loaded cablesections with a data speed of 1 500 bits/sec. In the case of 20 loaded cablesections the group delay distortion between 0.9 and 2.5 kc/s was equivalent toabout the length of 2 bits. Nevertheless, when /?,. = 10 :! , the resistance offeredby the data transmission system to white-noise disturbances was reduced byonly 2.5 db in comparison with a distortion-free data circuit.By permission of the Royal Board of Telecommunications, tests have beenmade over two carrier systems connected in tandem. The attenuation A BFand the group delay curve i BF of the circuit are shown in fig. lib and thecorresponding error curves in fig. 11a. To reduce the envelope delay distortiona delay equalizer is introduced which, together with the carrier system, producesthe group delay curve TJ and the attenuation curve A x . The curve p, showsthat the resistance offered by the data transmission system to white-noiseinterference is increased by 2 db when the error probability p,. = 10 '•'•. Othertypes of delay equalizer produce the curves r 2 and T S and p 2 and p 3 , respectively.As is shown by the examples, a comparatively rough group delayequalization is sufficient to improve the transmission channel considerably. Toachieve curve p 0 , however, an exact equalization of the group delay andattenuation is required.The test measurements carried out so far show that the L M Ericsson datatransmission system has good resistance to white-noise interference. Hence,satisfactory data transmission can be obtained by using this system over telephonecircuits which are subject to distortion and interference.71

Crossbar P. A. B. X. ARD 561A EILERTSEN & S KILANDER, TELEFONAKTIEBOLAGET L M ERICSSON. STOCKHOLMUDC 621.395.25LME 8372The excellent performance of the crossbar switch is being increasinglyulilized for private automatic exchanges. In the last few years L M Ericssonhas brought out several types of crossbar private exchanges. One of them isthe P.A.B.X. ARD 561 presented in this article.P.A.B.X. ARD 561, with capacity range 60-270 extensions and 6-40 exchangelines, is intended for medium-sized organizations. In its standarddesign it is equipped with all modern facilities both for internal and externa)traffic and, with certain supplementary equipment, can offer some valuableextra facilities such as automatic call-back, direct access, and paging.The P.A.B.X can be easily adapted to the organizational form of theenterprise. It operates quickly and surely with a minimum of maintenance.The extension telephones are ordinary instruments of the same type as inthe public telephone system. Special instruments such as loudspeaking telephones,secretary extensions etc.. may also be connected to the P.A.B.X.rFig. 1P. A. B. X. ARD 56172

\3- poleoutletA'? /tt# ^ ^fe^S; I ISelectingbarSelecting Sixthbar barA.position Normal Traffic FacilitiesC-positionB-positionInletFig. 2 X 2647Schematic diagram of 30-line crossbar verticalInternal callsInternal calls are initiated in the ordinary way by dialling the wanted number.A two- or three-digit numbering scheme may be used, according to thecapacity for which the exchange is equipped.Every extension with 0 as last digit can be given priority facility by simplestrapping in the exchange.A priority extension can enter a circuit on which an internal call is proceedingby dialling 2 after receipt of dial tone. A warning tone is sent on thecircuit to indicate that a third party is connected.The priority extension can now deliver his message or, if he wishes to speakto the called party alone, may request both parties to replace their handsets.A new ringing signal is thereupon sent automatically to the wanted extension.SLA SLB90ext. Q f. f*Fig. 3A and B stagesExternal callsClassification of extensionsThe extensions may be divided into four categories as regards external trafficfacilities:1. Unrestricted extensions, which, in addition to calls within the local area,may also dial their own trunk calls.2. Trunk-barred extensions, which may dial calls within the local area buthave restricted facilities for trunk calls (see Extra Traffic Facilities).3. Semi-restricted extensions, which cannot make outgoing calls but canreceive incoming calls.4. Fully restricted extensions, which are debarred from all external trafficand can make internal calls only.Outgoing callsTo make an outgoing call the extension dials a code digit, e.g. 0, for connectionto the public exchange, followed by the subscriber's number.If there are several exchange line routes, each route can have its own codedigit.Outgoing calls may also be made with the operator's assistancetch 1LV)Baa sa^ aasSNK \-Enquiry and transferWhile speaking to an external subscriber, an extension can make an enquirycall to another extension. For this purpose he dials one impulse followed bythe wanted extension's number. The enquiry call cannot be overheard by theexternal subscriber.tch 3LV)FDR-CY-If desired, the extension can transfer the call to the other extension withoutthe operator's assistance.Enquiry or transfer to an operator can be effected by dialling, for example,9.Fig. 4Extension line terminations on the multiplefield90 extensionsIncoming callsIncoming calls from the public exchange are received by one or moreoperators, who extend them to the wanted extensions by means of a keyseton their consoles (fig. 16).73

The exchange lines are directly represented on the operators' consoles hycalling lamps and answering buttons. An incoming call is signalled on twooperators' consoles simultaneously. The first operator to answer deals withthe call.The operators have various facilities for handling calls, of v\hich only someof the more important will be mentioned here.Waiting circuitIf the wanted extension is engaged, the operator can place the incomingcall on a waiting circuit ("camp-on" position). As soon as the extension becomesfree, the call is put through automatically. During the waiting periodthe operator is recalled every thirty seconds.Announcementof trunk callOn receipt of a long-distance or other urgent call, the operator can enter anengaged circuit to announce the call. A warning tone is at the same timeextended on the engaged circuit.ParkingIf the operator is engaged in handling one call when a new call arrives, shecan park the original connection while answering the new call. After extendingthe latter, she can return to the parked connection.Sequence callsIf a calling subscriber wishes to speak to several extensions in succession,the operator can connect the call in sequence.fij. 5Trunking diagramOn the completion of each conversation, the call is then returned to theoperator, who extends it to the next extension.Night serviceWhen the operators have completed their duties for the day. incoming callsare automatically directed to predetermined night-connected extensions, atwhich they are answered and from which they are transferred to the desiredextensions.90extFig. 6Connection to registerExtra Traffic FacilitiesARD 561 can. if desired, be equipped for various extra traffic facilities.The more important of these are briefly described below.M—C90 ext.M—cA90 ext.Fig. 7Internal callbetween extensions in different 90-line groupsGroup callsAny 20 extensions can be combined into groups of 5 or 10. each grouphaving a "group number". This provides access to any one of a number ofpersons engaged on similar work, such as card index operators, by dialling thecorresponding group number. The call then goes to a free extension within thegroup.A group extension can also be rung on his individual number.Automaticcall-backIf a calling extension meets the engaged condition, he need not ring againbut can be automatically connected as soon as the engaged extension becomesfree.74

90 ext.This is effected by dialling a code digit on receipt of the engaged signal andthen replacing the handset. When the called extension becomes free, a callbacksignal is extended first to the caller. When the latter answers, the calledparty is rung and connection is established.The extension initiating the call-back procedure is not blocked during thewaiting period but can use his telephone for other calls.Direct accessFig. 8Outgoing callConnection to public exchangePersons in managerial positions may be given the facility of direct accessto their subordinates. For this purpose their extension instruments must beequipped with a separate keyset. A subordinate can then be rung simply bypressing the appropriate key on the keyset without employing the dial.PagingAn audible or visual paging system can be connected to the P.A.B.X. forpaging of up to one hundred persons.Interworking with other private exchangesM—090 ext.By dialling a given code digit an extension can connect to another privateexchange and obtain access to its extensions.TrunkdiscriminationIf the public system allows subscriber-dialled trunk calls, the P.A.B.X. canbe equipped with a device for supervision of outgoing calls. Extensions maybe debarred from dialling trunk calls or allowed to dial trunk calls only oncertain routes. Non-restricted extensions are not supervised but can dial trunkcalls on any route.MeteringTrunk-barred extensions may also make trunk calls, but only with theoperator's assistance. If the public exchange transmits metering pulses, suchcalls can be metered.Fig. 9 X 2653Connection of register on enquiry callSchematic DesignGroupingThe crossbar switch used in ARD 561 has thirty 3-pole outlets.The outlets are arranged in three "levels"-/!, B and C-with ten outlets oneach (fig. 2).g—G90 ext.I—090 ext.Levels A and B are selected through the two actuated positions of the sixthbar, and level C through its neutral position. Thus on actuation of the sixthbar and one selecting bar a particular outlet is selected on level A or B. Onactuation of a selecting bar alone, a particular outlet is selected on level C.Since the switch has a capacity of 30 outlets, the extensions are grouped inmultiples of 30, making three principal groups of 90 extensions each. Connectingcircuits SNR, exchange lines FDR-C. etc.. are reached from each90-line group through two switching stages SLA and SLB (fig. 3).Fig. 10Enquiry callx 2654The first stage SLA consists of three ten-vertical switches, each containingtwo multiple fields I and II (fig. 4). Each multiple field represents five verticals(V 1-V 5 and V 6-V 10).A group of 90 extensions is connected to these multiple fields in such away that every extension line appears on two fields.75

Fig. 11Trunking diagramThe principle of the twisted multiple is employed (fig. 4). This implies that agroup of ten extensions shares the verticals in one multiple field with certain10-line groups but, in the other multiple field in which it is represented, withcertain other 10-line groups. This arrangement provides the optimum accessibility.The 30 inlets of the SLA stage are wired to the outlets of the SLB stage, soforming the multiple field in this stage. The inlets of the SLB stage are thereafterconnected to the various switching units SNR, FDR-C, etc.The switching units may be defined as common and individual units. Thecommon units, comprising register REG and marker M, are used for thesetting up of calls and are released as soon as this has been done.The individual units—connecting circuits SNR and exchange lines FDR-C,etc.—are occupied until the call is completed.Fig. 12Circuit after transfer of a callThe connecting circuits are reserved for internal traffic and are not usedon external calls. Every 90-line group has five connecting circuits allotted to itfor normal traffic, and access to five common connecting circuits under peaktraffic conditions.Enquiry and transfer are effected through special enquiry units FFR. andso do not occupy a connecting circuit (see trunking diagrams, figs. 5 and 11).Initiation of call by extensionWhen an extension A raises his handset, his line is first identified by themarker. The extension is thereafter connected—via a connecting circuit SNR—to a free register REG, which returns dial tone. The marker restores (fig. 6).90 extIn order that the registers shall not remain occupied unnecessarily long,they are equipped with automatic time release which enters into operation ifmore than 5-8 seconds elapses before dialling is started.The extension can now dial an internal number or the digit for connectionto the public exchange. In both cases the marker is seized once again. If thecall is internal, the marker identifies the called extension B and sets up theconnection via the already seized connecting circuit SNR. A ringing signal istransmitted and. as soon as B answers, the connection is established (fig. 7).Fig. 13Extension of incoming callOn an outgoing call the marker selects a free exchange line. The connectingcircuit SNR on which the extension was connected to the register is immediatelycleared and the extension is connected to the exchange line equipmentFDR-C. The loop is closed to the public exchange HC, which returns dial toneto the extension (fig. 8).76

\To assure that outgoing calls can be made even in the rare case that allconnecting circuits are engaged, the switchboard has been equipped withauxiliary connecting circuits (HSNR). The extension is in such case connectedvia an auxiliary connecting circuit to the register and dials the exchange code.As soon as he obtains a free exchange line, HSNR is restored just like anordinary connecting circuit. The auxiliary connecting circuits are used exclusivelyfor this purpose and are never accessible for internal calls. If anextension attempts to make an internal call via an auxiliary connecting circuit,busy tone is returned.Enquiry and transferIf during an external call an extension wishes to make an enquiry call, hedials one impulse. The exchange line FDR-C is then switched to a free enquiryunit FFR and is extended thence to a register REG (fig. 9). The registerreturns tone to the extension, who can now dial the internal number.The marker then sets up the call in the same way as an ordinary internalcall. The register restores (fig. 10).For transfer of the call, the marker switches the exchange line to the newextension and the enquiry unit is released (fig. 12).Incoming callAn incoming call from the public exchange is signalled on the operator'sconsole FMA. When the operator answers, the exchange line is switched tothe operator's equipment FMT and FMA via a special switching stage FDKThe operator is now in connection with the calling subscriber.She extends the call with the aid of the keyset on her console. The extensionnumber is stored by a register in FMT.The marker then sets up the connection between the subscriber and thewanted extension B in the same way as between two extensions. FMT andFMA are restored (fig. 13).Fig. 14Rack unitMechanical StructureRacks and relay unitsWhen installed to full capacity, the P.A.B.X. consists ot eight rack units(fig. 14). The dimensions of all rack units are: height 2.455 mm (8 ft.), width1,025 mm (3'4"), depth 250 mm (10").One additional rack unit is required if extra traffic facilities are to be provided.All racks are supplied factory-wired with plastic-insulated wire.Relays and switches are combined into units which connect to the racks byplug and jack (fig. 15). Each unit has an enamelled metal cover as protectionagainst dust and damage.Racks, crossbar switches, relays etc. are made to withstand tropical climatesand are in other respects of the same high quality as in L M Ericsson's publicsystems.Fig. 15Relay unit with crossbar switch77

Fig. 16Operator's consoleOperator'sconsoleThe operator's console is modernly designed with casing of pastel-greypolystyrene (fig. 16). The buttons are formed as "lamp-buttons", i.e. withlamps built into the buttons, which reduces the size of the console andsimplifies the work of the operator. The lamp-buttons are made up in sets(fig. 17) which plug into the console. The sets can be easily released for inspectionor replacement.The operator's console has space for five counters, which are fitted if theexchange is to have metering facilities.The handset—also in grey pastel—is characterized by its low weight. It ismade for plug-and-jack connection.SignallingequipmentFig. 17 X 2661Lamp-button set for five exchange linesThe ringing voltage, 85 V, 40-60 c/s, is supplied from the commerciallighting system via a transformer. In the event of a power failure a standbypower unit is automatically switched into circuit to supply the ringing voltage.If desired, a signal generator or transistor unit for 25 c/s can be connected.The tones have a frequency of 425 c/s and come from a transistor unit inthe signal equipment. The output voltage can be varied.600 1025 1025 102510251025600I POM er equipment| SVSi V G Vfee - cSlV GvFORCSLV GVFDK-CITFDR-C0001 0 uJ1ARD 561 operates on 48 V, which, however, may fluctuate between 42and 54 V.TThe power equipment consists of a storage battery and automatic charger.2665Hl»^M.D.F.51The capacity of the power equipment depends ... on the size of the exchange.The average busy hour r power consumption in a fully installed s> system isnormally lallv about 25 A A.Fig. 18Exchange roomET Equipment for extra traffic facilitiesT Work benchB BatteriesR ChargerInstallation and maintenanceThe exchange is very easy to instal. The rack units are set up in pairs backto-back,the pairs being interconnected by plug-ended cables. The installationthus involves no soldering (figs. 18 and 19). It is still further facilitated by the78

fact that extension and exchange lines connect to the exchange by plug andjack. The exchange needs very little maintenance after its installation. Nopreventive maintenance whatsoever is required. Maintenance costs can thereforebe kept to a minimum.M.D.F.If the installation comprises less than 180 extensions, the M.D.F. may consistof a simple set of terminal blocks mounted on the end of one of the racks.For larger exchanges a more complete M.D.F. is recommended, type BAB.with protector strips and test jacks.Technical DataCapacityThe maximum capacity is:270 extensions 3 operators' positions40 exchange lines 6 registers20 connecting circuits 6 enquiry unitsThe exchange is made up of detached units which plug into one or moreracks. The initial capacity can therefore be easily adapted to the immediaterequirements of the organization, and further units added as desired.Usual numbering and codesFor a fully installed exchange the numbering scheme is as follows:110-199210-299310-399If only 60 extension lines are installed, two-digit numbers can be used, e.g.10-69.Code foroutgoing calls: 0 or 9enquiry to other extension: /enquiry to operator: 9 or 0tie lines: 6, 7, 8paging: 4 for paging call, 5 for answerautomatic call-back: 3 after busy tonepriority call: 2 after busy toneTraffic capacity: The SLV stage is dimensioned for 14.5 erlangs per groupof 90 extensions (outgoing and incoming), i.e. 0.16 erlang per extension with2°/oo congestion.Feed: Individual feed 2 X 400 Q, adjustable to 2 X 250 Q.Power consumption: 0.6 A on an internal call, 0.5 A external.Clearing: The connecting circuits can be strapped for first or last party release.Line resistance: The resistance of an extension line may be up to 1.000 Q,including the resistance of the telephone set.Dialling: The dial may have any desired numbering and impulse ratio. Thedialling speed should normally be 8-13 IPS, but the exchange can be adaptedto 20 I.P.S.Attenuation: The transmission attenuation on internal and external calls isbelow 1.3 db measured between 300 and 3,400 c/s.The crosstalk attenuation within the same frequency range is above 78 db.79

Duration Meter VMF 81N E R I C S S O N , A K T I E B O L A G E T E R M I , K A R L S K R O N AUDC 621.317.787.2LME 7953There are many fields of engineering in which plant and apparatus exhibitvariations in utilization, speed, output, temperature etc. For the proper operationof such plant it is often essential to have a knowledge of these processes.ERMI has designed a duration meter, type VMF 81, for simple and quickanalysis of the variations in the quantities of interest.By the duration of a load or other quantity is meant the aggregate periodduring which the quantity is attained or exceeded. If a graph is made of theduration of all quantities, and they are arranged in order of magnitude withoutregard for their sequence in time, a duration curve is obtained which presentsa clear and easily interpreted picture of the magnitude and variation ofthe quantities during a specific period.This curve can naturally be obtained by other means with a recording instrumentof some kind, but in such case the values will be arranged in chronologicalorder instead of in order of magnitude; and if the measurement coversa long period, the task of analysing the curve and converting it into a durationcurve is a very laborious one.Fig. 1 X 7847Duration meter VMF 81; right with reardoor openTerminal block for mains voltage and signal generatoris seen inside the door.ApplicationsThe duration meter VMF 81 was designed primarily for the use of electricityproducers and consumers. The duration curve of the load in an entireutility system, on a single line or of a particular consumer is of very greatsignificance for the solution of many engineering and economic problems

\concerned with the installation and operation of the plant, such as calculationsof rates and of line losses. In this case the duration meter is used in conjunctionwith a kilowatt-hour meter equipped with a contact device which deliversimpulses at a frequency proportional to the power.In its present form, however, the meter can be used for many other electricaland mechanical applications such as the measurement of flowing liquidsand gases, of various kinds of traffic intensity, and of rotary movements, e. g.the most utilized speeds of motors, etc. The only requirement is that a signalgenerator which delivers impulses at a frequency proportional to the quantityto be studied can be fitted to the apparatus concerned.PrincipleAs stated, the construction of the duration curve is based on a signal generatorwhich, during a given period, delivers a number of impulses proportionalto the quantity to be measured - kWh, cubic feet of gas, or revolutionsof a motor - but, as the quantity is related to a given interval of time, the impulsesalso represent the mean value per unit of time in kW, cu.ft./hr. orr.p.m. The duration meter contains a number of registers so arranged thatduring a fixed period of time - the recording period - they selectively accumulatethe impulses in the order of their delivery from the signal generator.The record on every register, after repeated series of impulses, will thereforerepresent the number of recording periods during which the register has beenin operation. Every impulse consequently corresponds to a given mean valueduring the recording period; if, for example, four impulses have been deliveredduring the period, the mean value of the quantity measured during the periodwill be 4 times the impulse value, and the 1 st—4th registers will have beenactuated. On the first register is read the number of periods during which 1 Xthe impulse value was attained, on the second register 2 X the impulse value,and so on.The result is reproduced graphically by plotting the sequence numbers orcorresponding values of the registers as ordinates and the records or correspondingnumber of seconds, minutes or hours as abscissa. The resulting pointsare joined together into a curve which shows the duration over the entirerange measured.Under the above circumstances the value would be confined to even multiplesof the impulse values, i. e. the test points on the ordinate would be evenly dividedalong the whole curve. Sometimes, however, one is not interested inthe entire curve but only in a small part of it, but in this part a very ac-Effectivelevel^No. 12 (230kW)No. II (210 kW)vNo. 10 (200 kW)No. 9 (190 kW)^No. 8 (ISO kW)^No. 7 (170 It W)No. 6 (160 kW)JVo. 5 (1 SO kW)No. 4 (130 kW)No. 3 (110kW)Fig. 2» Ja 'Duration curve for an electricity undertakingxNo. 2 (60kW)The measurement covers one month. The power inkW is read along the ordinate and the time inhours along the abscissa. The area within the curverepresents the total energy consumption in kWh.gis/er No. I (10 kW)81

curate analysis is desired. This is provided for in Ermi's duration meter throughthe fact that the 12 registers can be connected at choice to a large numberof test levels - altogether 29. The test points can thus be adapted entirely tothe conditions for each individual apparatus under observation. In fig. 2. representingthe duration curve for an electric load, the registers - the test points- have been concentrated to the upper portion of the curve, which is the partof interest for the utilities' rate calculations.Mechanical DesignDuration meter VMF 81 consists of a recording section with twelve registers,a timer for determining the length of the recording period, and a power unitwith rectifier for driving the components.The only external terminations required are therefore to 1 10, 127 or 220volts a. c. and to a signal generator with contact device fitted with a makecontact.The meter is enclosed in a case, the front and rear of which can be opened.Meter data can therefore easily be reset at the site of installation and thecomponents are readily accessible for inspection and service.Recording unitThe heart of the recording unit (figs. 3 and 4) consists of two rotary 30-step selectors RVF 1009 and twelve registers, ordinary telephone subscribers'meters, HSA 2002.The impulses from the signal generator are fed via relays to one of the30-step selectors (4), which serves as impulse collector; i. e. all impulses fromthe signal generator - " primary impulses" - enter this selector and, with theaid of the switch {8), one can select at choice the number of impulses to beFig. 3Duration meter with front door open4, 5781112131430-step selectorsRegistersPrimary secondar)TimerRelavsRectifierMains transformerimpulse switchx 837915 Terminal block for change of impulse duration82

0 ®Fig. 4 X 8380Duration meter with rear door open1 Terminal block2 Mains voltage switch3 Fuses4, 5 30-step selectors6 Jack strip for connection of registers8 Primary secondary impulse switch9 Entry for register leads10 Connector sockets for checking total numberof impulses received and recording periodscollected before a "secondary impulse" is sent on. The impulse collector thusserves as range switch since the number of primary impulses is multipliedby the number set on the switch. Any multiplicand between 1 and 25 can bechosen except 13, 17 and 19.The secondary impulses from the impulse collector are fed to the second30-step selector (5) - the level distributor - which distributes the impulses tothe desired level. There are 29 levels, represented in the meter by a strip of29 jacks (6), into which the twelve registers (7) can be plugged in any desiredcombination. The jack strip contains also two jacks (10) for recording thetotal number of primary impulses received and the number of recording periods.Two registers may thus be allocated for this purpose if desired.Signal generators with different impulsing characteristics can be connectedto the duration meter. The impulse duration, however, should not be less than0.08-0.1 second.TimerThe timer (//) is of standard Ermi type. It consists of a self-starting synchronousmotor which, via gearing, actuates a contact springset with makefunction. The closure time is 15 seconds. By change of gearwheels the durationof the recording period can be adjusted to 5, 10, 30, 60 or 120 minutes.Power unitAll components - 30-step selectors, registers etc. - are designed for 24volts d. c. But for greater convenience in use, the instrument has been equippedfor direct mains connection through a power unit consisting of a transformer(14), rectifier (13) and voltage switch (2). The transformer is protectedby two fuses (3). The voltage switch provides tappings for 110, 127 or 220 Vmains.83

Technical DataTappings: 110, 127 and 220 V, 50 c/s.Permissible voltage variation: ± 10 %.Permissible temperature variation: - 10 to + 40° C.Power consumption: approx. 75 mA at 220 V, 50 c/s, momentary values ofabout 150 mA.Load on impulse contact of signal generator: 12 mA at 24 V d. c.Number of test levels: 29 + 2 for checking total number of recording periodsand total number of primary impulses.Number of registers: 12 with 5-digit drums. Separate set of 20 registers forrecessed mounting can also be provided.Recording period: standard 15 mins.: 5, 10, 30, 60 or 120-min. periods canbe arranged if desired.Max. number of primary impulsesper recording period . . 725Restoring timeWeightDimensionsless than 1 sec.about 1 3.5 kg (30 lb).240 X 160 X 360 mm (9Va X 6V4 X 14V« in.).

\NEWS/romAll Quarters of the WorldLarge Orders for L M EricssonNew Danish Contractfor 50 million KronorL M Ericsson and the CopenhagenTelephone Company havesigned a contract for continued deliveriesof crossbar equipment for extensionof the Danish automatic network.The contract covers the deliveryand installation of automaticexchange equipment for 100,000 subscribers,as well as automatic trunkequipment.The Copenhagen Telephone Companyis the largest of the three privatetelephone operating companiesin Denmark, its area comprising Zealandwith Copenhagen, the islands ofLolland-Falster and Bornholm, withaltogether some 500,000 subscribers.A large part of the equipment forthe Danish market is manufacturedby Ericsson's Danish associates, TelefonfabrikAutomatic A/S, of Copenhagen,who in the past year havegreatly expanded their production resourcesfor crossbar equipment. Cableand power plant for the telephoneexchanges are also being suppliedby Danish factories.The new contract covers equipmentfor at least 50 million Kronor.key to operate on the Ericsson crossbarsystem, and 15,000 telephone instruments.After the installation of this equipmentL M Ericsson will have suppliedto Turkey automatic exchanges covering123,600 lines at 44 towns throughoutthe country.Lebanese Telephone Networkto be Extended to 100,000LinesIn hard competition with French,Italian, Japanese and German telephonemanufacturers, L M Ericssonhas been awarded a contract by theLebanese P.T.T. for automatic exchangeequipment and telephone instrumentsto a value of some 10 millionKronor. The installation of thisequipment will bring the Lebaneseautomatic network up to nearly100,000 lines, all of which have beensupplied by L M Ericsson.New Telephone Factoryin AustraliaA new telephone factory is to bebuilt at Broadmeadows near Melbourneby L M Ericsson's Australiansubsidiary, L M Ericsson-Trimax Pty.Ltd. The first stage is to compriseabout 120,000 sq. ft. of factory andoffice accommodation to permit expansionof the production of telephoneexchange and other telecommunicationmaterial. Substantial ordersfor modern crossbar switchingequipment for automatic exchangesof the Australian Post Office will bemet by the new factory, which is expectedto be in operation by the endof next year.Canada to Install Exchangesfor Intercontinental CallsL M Ericsson has received an orderfrom Canadian Overseas TelecommunicationCorp. for two automaticexchanges for intercontinentalcalls. They are to be installed atMontreal and Vancouver and willlink the national Canadian networkwith the Atlantic and Pacific cablesof the British Commonwealth roundthe-worldproject. The exchanges willconnect calls between Canada, Europeand Australia, and will be ofEricsson crossbar type. The value ofthis first order is only about 1 millionKr., but the installation carries withit a considerable prestige value.(Below) The new office building of L M EricssonLtd. in Montreal.30,000 Subscriber Linesfor TurkeyL M Ericsson has signed a newcontract with the Turkish P.T.T. forthe delivery of telephone equipment,the main item being the addition of30,000 subscriber lines at automaticexchanges already supplied by L MEricsson. The contract also includesa new 1000-line exchange, which willbe the first public exchange in Tur-85

Holger OhlinThe announcement of Holger Ohlin'sdeath on Friday the 17th ofAugust did not come entirely unexpectedlyto those who had followedhis stubborn struggle against illnessduring his closing months. The will towin was strong in him to the last.Holger Ohlin's lifework was devotedalmost entirely to L M Ericsson.He entered the company's serviceas Head of the Treasury Departmentin 1928. and in 1931 wasappointed Vice President and Headof Central Sales. During the troublesomeperiod for the company thatfollowed on the Kreuger crash, greatdemands were placed on his knowledgeand experience; and then, asin the difficult work of reconstructionin the subsequent years, his abilitiesand intelligence were a greatasset to the company. In conjunctionwith the reorganization of themanagement in 1940 he was appointedChief Financial Officer, being the firstholder of this appointment. From1954 to 1961 he held the powersand responsibilities also of ExecutiveVice President.Holger Ohlin held degrees in economicsand law, a combination whichproved to be of great value to him.He also had a wide knowledge oflanguages, which meant that he coulddevote considerable attention to theforeign problems of the company,both those of an economic and financialnature and those concerned purelywith business management. Hedevoted special interest to the Italiansection of the Group, where the problemshave been many and difficult.His efforts were acknowledged in theaward of the Order of Knight Commanderof Merito Italiano, a distinctionon which he rightly placed greatvalue.Despite the heavy load of workinvolved in his Ericsson appointments—he was also member of a number ofboards within the Group—he foundtime for various public assignments,in the conduct of which his sagacityand sound knowledge were highlyappreciated. When Holger Ohlin retiredon pension last year at the ageof 65. we in the management of thecompany hoped that we might continueto draw on his fund of experiencefor a long time to come.He himself looked forward to a periodwhich would give him the freedomto devote his time to many86in Memoriamquestions outside his previous sphereof work. But fate decreed otherwise.Holger Ohlin, the able, versatileand always helpful administrator, theconfident, cheerful and kindly Scanian,is no more. Among those whomourn his departure are the manythousands of Ericsson employees whojoin with me in a word of warmgratitude to our friend for what hehas meant to us all.Sven Ture Aberg120 British RailwaySignal Engineers VisitL M EricssonThe Institution of Railway SignalEngineers (IRSE) celebrated its halfcentenaryin 1962. The annual visitpaid by the Institution to railwaysignalling plants and manufacturersinside or outside the British Isleswas this year made to Sweden, wherethe State Railways and L M Ericssonhad the pleasure of cooperatingin the arrangements for the IRSEGolden Jubilee Convention.The party arrived in Stockholmon May 9 and immediately proceededto the Midsommarkransen offices ofL M Ericsson, where they were welcomedby the president, Sven T.Aberg. The group was able to studyL M Ericsson's products in the ExhibitionRoom and to make a quicktour of the factory.In the days that followed. IRSEvisited the Stockholm Central Station,where the State Railways demonstratedthe relay interlockingplant at present under constructionthere, for which L M Ericsson hadarranged a model of the track diagramto be used in the new plant.The State Railways had also arrangeda display of the signalling equipmentthey employ—principally of Ericssonmake.IRSE thereafter visited the AngeC.T.C. plant, the largest in Europe,also delivered by L M Ericsson.Ericsson C.T.C. forSpanish RailwaysCia Espafiola Ericsson and L MEricsson have received orders fromthe Spanish Railways, RENFE, forC.T.C. equipment on the Valcncia-Sagunto line, the southernmost sectionof the Valencia-Barcelona line.Cia Espafiola Ericsson is to supplyrelay interlockings for the seven remote-controlledstations, and blocksbetween them, and L M Ericsson isto supply the remote control equipments.Five of the seven stations havetwo main tracks and the other twostations three main tracks. The lineis single track, 20 miles in length,and normally carries 50 trains a day.The C.T.C. system will he ofstandard Ericsson type with keyboardoperation and a semicircular,sectional track diagram carrying indicationlamps only. The plant is tobe in operation by 1963.Spain will be the eleventh countryto which L M Ericsson has suppliedC.T.C. equipment.51,720 Kronor inAnnual LME GrantsThe Telefonaktiebolaget L M EricssonFoundation for the Promotionof Electrotechnical Research hasmade grants amounting to 16,000Kronor from the year's funds to eightpersons.The company's Foundation forTravel and Other Educational Grantshas awarded 35,720 Kronor to 25employees of the Ericsson Groupand to 5 employees of the SwedishTelecommunications Administration.

\President Tubmanat L M EricssonLiberia's President, William Tubman,paid an official visit to Swedenat the end of September, in the courseof which he made a call at L MEricsson's Midsommarkransen factory.The President, accompanied bythe Prime Minister, Tage Erlander,Cabinet Minister, Sven af Geijerstam,and a large following, was welcomedby the Chairman of the Board, DrMarcus Wallenberg. After a briefaccount of the company's activitiesby President Sven T. Aberg, the partywas shown round the ExhibitionRoom. Mr. Aberg presented the Presidentwith a set of Ericofons in theLiberian colours, red, white and blue,and an Ericovox.L M Ericsson's first large orderfrom the Liberian government hadbeen obtained in September 1%1. Itcomprised local automatic exchangesand outside plant for Monrovia andother towns to a value of nearly 9million kronor. A further contractwas recently concluded with Liberiafor the supply of carrier equipmentfor the national trunk network.President William Tubman with (right) DrMarcus Wallenberg and Mr. Sven T. Abergand (left) Mr. B. Thisell.The inauguration at Katmandu, capital of Nepal, of the1,000-line automatic exchange of Ericsson type ARF 101.King Mahendra Bir Birkram Shah Deva cuts the tapeacross the entrance to the Katmandu Telephone Exchange.On the left is Dhundi Raj, Secretary of the Minister ofCommunications, and on the right Chief Engineer HerambaPrasad I'padhyaya.(Above) From left: Director General Abdul Jabbar Ismail, Mr. Usama, andGeneral M. A. Baghdadi from the Iraq P.T.T. on a visit to Midsommarkransen.87

Ericsson MaintenanceConferenceCrossbar Comes to MalayaEricsson crossbar systems have begunto meet with an increasing demandin Southeast Asia. Public crossbarexchanges are already operatingin Burma, Thailand and Indonesia,and new exchanges are being installed.In March L M Ericsson was invitedby Malayan Telecoms to runan introduction course in crossbartechnique for exchange and installationsupervisors from the whole ofthe Malayan Federation. Concurrentlywith this course, an informationconference on the crossbar systemwas arranged which was attended bythe Central Operations Managementof Malaya Telecoms. The course andthe conference, both of which wereheld at the training centre of MalayaTelecoms at Kuala Lumpur, met withan enthusiastic reception, and theknowledge imparted will undoubtedlybe of value to the participators.For the first crossbar P.A.B.X.'s aresoon to be installed in Malaya—acountry whose telephone density isabove the average for Asia and isgrowing strongly.(Above) Some of the participators during abreak in the information conference. (Fromleft) Ericsson engineers A. Uvhagen, K. Albertssonand H.S. Andersson; L. Bywater,Lee Chye Watt, G. A. Langley, of Telecoms;and F. Loh of Singapore Telephone Board.At this year's maintenance conference,which was held in Stockholmfrom June 4 to June 8, most of theLatin American telephone administrations,as well as the Swedish, wererepresented. As in the preceding year,the conference dealt with "integratedmaintenance", comprising the waysand means of rational supervision andcontrol of the functioning of telecommunicationsplant. The term "integratedmaintenance" is here takenas meaning that the same principlesare applied in the maintenance of exchangeequipments, long distance andlocal cable networks.Since 1956. at maintenance conferencesand elsewhere, L M Ericssonhas advocated a radical reexaminationof the maintenanceprinciples as earlier practised. Theform of maintenance recommendedby L M Ericsson for automatic exchangesis called "controlled correctivemaintenance". These recommendationswere discussed at this year'sconference, as also different aspectsaffecting the choice of policy in themaintenance of telecommunicationplant.A special exhibition, "Maintenance62", had been arranged for the conference,at which were shown theequipments considered necessary forrational maintenance of Ericssonautomatic exchanges (see photo belowleft).The conference devoted special interestto the equipments for mechanizationof maintenance supervision,and the new methods of maintenanceorganization which the equipmentsrequire were extensively discussed.After the conference a round tripwas arranged to the local telephoneadministrations in Gothenburg, Aarhus,Odense and Copenhagen. Someof the Danish P.T.T. plants for longdistance telephony were also visitedin Copenhagen. The Swedish andDanish administrations gave a fullaccount of their experience of theoperation of subscriber-controlled networks.Sixteen administrations and operatingcompanies had sent delegates tothe year's conference. Representativesof the Swedish Air Force were alsopresent as observers. The discussionstook place in Spanish and Englishwith simultaneous interpretation betweenthe two languages.88

UDC 621.394.3LME 81WIDL, W: An Experimental Data Transmission System. Ericsson Rev.39(1962): 3, pp. 62—71.During the last few years technical development has entailed an everincreasingdemand for the transmission of vast amounts of data betweengeographically separated centres. Particularly military defence systems arein urgent need of data transmission equipment permitting higher speeds.It is therefore natural that the system described in this article should havebeen developed to the order of Kungliga Flygforvaltningen (the RoyalSwedish Air Force Administration), which also drew up the required basicspecification. This resulted in the construction of a phase-shift data transmissionsystem permitting the transmission of binary digits at a speed ofup to 1500 bauds over telephone circuits. In the article a description isgiven of the function and construction of the system. In conclusion a fewtest results are given.EILERTSEN. A & KILANDER, S: Crossbar P.A.B.X.Rev. 39(1962): 3, pp. 72—79.UDC 621.395.25LME 8372ARD 561. EricssonThe excellent performance of the crossbar switch is being increasinglyutilized for private automatic exchanges. In the last few years L M Ericssonhas brought out several types of crossbar private exchanges. One ofthem is the P.A.B.X. ARD 561 presented in this article.UDC 621.317.787.2LME 7953ERICSSON, N: Duration Meter VMF81. Ericsson Rev. 39(1962): 3, pp.80—84.There are many fields of engineering in which plant and apparatus exhibitvariations in utilization, speed, output, temperature etc. For the properoperation of such plant it is often essential to have a knowledge of theseprocesses. ERMI has designed a duration meter, type VMF 81, for simpleand quick analysis of the variations in the quantities of interest.

e Ericsson GroupAssociated and co-operating enterprises* EUROPE •DenmarkL M Ericsson A/S Kebenhavn F,Finsensvej 78, tel: Fa 6868, tgm:ericssonTelefon Fabrik Automatic A/SKobenhavn K, Amaliegade 7, tel:C 5188, tgm: automaticDansk Signal Industri A/S KebenhavnF, Finsensvej 78, tel: Fa6767, tgm: signalerFinlandO/Y L M Ericsson A/B Helsinki,Fabianinkatu 6, tel: A8282, tgm:ericssonsFranceSoci^te des T£l6phones EricssonCo/ombes (Seine), Boulevard de laFinlande, tel :CHArlebourg 35-00,tgm: ericssonParis 17e, Rue de Courcelles,tel: CARnot 95-30, tgrn: ericAteliers Vaucanson, Paris XX, BP. 28.20,tel: MENilmontant 83-40tgm: atelcansonGreat BritainSwedish Ericsson Company Ltd.London, W. C. 1, 329 High Holborn,tel: Holborn 1092, tgm:tel ericProduction Control (Ericsson)Ltd. London, W. C. 1, 329 HighHolborn, tel: Holborn 1092,tgm: productrol holbItalySETEMER, Soc. per Az. Roma. ViaG. Paisiello 43, tel: 868.854,868.855, tgm: setemerSIELTE, Soc. per Az. Roma, C. P.4024 Appio, tel: 780221, tgm:sielteFATME, Soc. per Az. Roma, C.P.4025 Appio, tel: 780021. tgm:fat meAgencies- EUROPE •BelgiumElectricite et Mecanique Su^doisesBruxelles 5, 56 Rue de Stassart,tel: 111416, tgm: electrosuedeGreece"ETEP" S. A. Commercials &Technique Athens 135, 11 LycavettusStreet, tel: 617041, tgm:aster-QthinaiIcelandJohan Ronning H/F Reykjavik,P. O. B. 45, tel: 14320, tgm:ronningIrelandCommunication Systems Ltd.Dublin 4, 138 Pembroke Road,Ballsbridge, tel: 680787 tgm:crossbarYugoslaviaMerkanlile Inozemna ZastupstvaZagreb, Po5t pretinac 23, tel:36941, tgm: merkantile, telex:02-139• ASIA •BurmaBurma Asiatic Co. Ltd. EricssonDepartmentRangoon, P.O.B. 1008,tel: 10999, tgm: ericssonCambodiaThe East Asiatic Company Ltd.Phnom-penh, P.O.B. 129, tel:762-1070-1071, tgm: pyramideCeylonVulcan Trading Co. (Private) Ltd.Colombo 1, New Caffoor Building,40. Church Street, tel: 36-36, tgm:vultraChinaThe Ekman Foreign AgenciesLtd. Shanghai, P. O. B. 855, tel:16242-3, tgm: ekmansNetherlandsEricsson Telefoon-Maatschappij,N.V. Rijien (N.Br.), tel: 01692-555,tgm: erictelden Haag—Scheveningen, 10, Palacestraat,tel: 55 55 00, tgm:erictel-haagNorwayA/S Elektrisk Bureau Oslo NV, P.B.5055, tel: Centralbord 4618 20.tgm: elektrikenA/S Industrikontroll Oslo, Teatergaten12,tel: Centralbord 335085,tgm: indtrollA/S Norsk Kabelfabrik Drammen,P. B. 205, lei: 1285, tgm: kabelA/S Norsk Signalindustri Oslo,P. B. Mj 2214, tel: Centralbord56 53 54, tgm: signalindustriPortugalSociedade Ericsson de Portugal,Lda. Lisboa, 7, Rua Filipe Folque,tel: 57193, tgm: ericssonSpainCia Espanola Ericsson, S. A.Madrid 13,Torre de Madrid 3erpiso, oficina 9, Plaza de Espana,tel : 241 1400, tgm : ericssonSwedenTelefonaktiebolaget L M EricssonStockholm 32, tel: 19 00 00, tgm:telefonbolagetAB Alpha Sundbyberg, tel:282600,tgm: aktiealpha-stockholmAB Ermex Soma, tel: 82 0100,tgm: elock-stockholmABErmi.Kar/sfcrona 1, tel: 23010,tgm: ermibolag-karlskronaAB Rifa Bromma 11, tel: 26 26 10,tgm: elrifa-stockholmAB Svenska Elektronror Stockholm20, tel: 44 03 05, tgm:electronicsCyprusZeno D. Pierides Larnaca, P.O.B.25, tel: 2033, tgm: pieridesHong KongThe Swedish Trading Co. Ltd.Hongkong, P. O. B. 108, tel:35521-5, tgm: swedetradeIranIrano Swedish Company AB,Teheran, Khiabane Sevom Esfand28, tel: 367 61, tgm: iranoswedeIraqUsam Sharif Company W.L.L.Baghdad, Sinak-Rashid Street, tel:87031, tgm: alhamraJapanGadelius & Co. Ltd. Tokyo C,P. O. B. 1284, tel: 408-2131, tgm:goticusKoreaGadelius & Co. Ltd. Seoul, I. P. O.Box 1421,tel: 2—9866, tgm: gadeliuscoKuwaitLatiff Supplies Ltd. Kuwait, P. O. B.67, tel: 2404, tgm: latisupLebanonSwedish Levant Trading (EMeB. H£lou) Beyrouth, P. O. B. 931,tel: 231624, tgm: skefkoPakistanVulcan Industries Ltd. KarachiCity, P. O. B. 4776, tel: 325 06,tgm: vulcanPhilippinesU.S. Industries Philippines Inc.Manila P. R., P. O. B. 125, tel:8-93-51, tgm: usiphilSaudi ArabiaMohamed Fazil Abdulla ArabJeddah, P. O. B. 39, tel: 2690, tgm:arabSingapore and MalayaThe Swedish Trading Co. Ltd.Singapore 1, 42 Chartered BankChambers, Battery Road, tel:249 64, tgm: swedetradeL M Ericssons DriftkontrollaktiebolagSolna, tel: 27 27 25, tgm:powers-StockholmL M Ericssons SignalaktiebolagStockholm Sv, tel: 68 07 00, tgm:signaibolagetL M Ericssons Svenska ForsdljningsaktiebolagStockholm 1, Box877, tel: 22 31 00, tgm: ellemMexikanska TelefonaktiebolagetEricsson Stockholm 32, tel:190000,tgm: mexikanSieverts Kabelverk AB Sundbyberg,tel: 282860, tgm: sievertsfabrik-stockholmSvenska Radioaktiebolaget Stockholm12, Alstromergatan 14, tel:22 31 40, tgm: svenskradioAB Ostmarks Ldsfabrik Eskilstuna,Munktellsgatan 5, tel: 31455SwitzerlandEricsson Telephone Sales Corp.AB, Stockholm, ZweigniederlassungZurich Zurich, PostfachZurich 32, tel: 325184, tgm: telericssonWest GermanyEricsson Verkaufsgesellschaft m.b. H. Diisse/dorf, Postfach 2925,tel: 844 61, tgm: erictel. ASIA •IndiaEricsson Telephone Sales CorporationAB New Delhi 1, P.O.B.669, reg.mail: 1/3 Asaf Ali Road(Delhi Estate Building), tel: 228512,tgm: indericCalcutta, P. O. B. 2324, tel: 45-4494, tgm: indericIndonesiaEricsson Telephone Sales CorporationAB Bandung, DjalanDago 151, tel: 8294, tgm: javericDjakarta, Djalan Gunung Sahari26, tel: Kota 22255, tgm: javericLebanonTelefonaktiebolaget L M Ericsson,Technical Office Beyrouth,Rue du Parlement, ImmeubteBisharat, tel: 252627, tgm: ellemTurkeyEricsson Turk Ticaret Ltd. $irketiAnkara. Adil Han, Zafer Meydani,Yenisehir, tel: 231 70, tgm:ellemSyriaGeorgiades, Moussa & Cie Damas,Rue Ghassan, Harika, tei:1-02-89, tgm: georgiadesThailandEricsson Agency Office, TelephoneOrganization of ThailandBangkok, Ploenchitr55183, tgm: telthai. AFRICA •Road, tel:EthiopiaSwedish Ethiopian CompanyAddis Ababa, P. O. B. 264, tel:11447, tgm: etiocompGhanaThe Standard Electric CompanyAccra, P.O.B. 17, tel: 627 85, tgm:standardKenya, Tanganyika, Uganda,ZanzibarTranscandia Ltd. Nairobi, Kenya,P.O. B. 5933, tel: 21931, tgm:transcandaLiberiaSwedish Agencies Liberia Co.Monrovia, P.O.B. 506, tel: 745,tgm: salco (Except sales to publicinstitutions)LibyaThe Gulf Trading Co. Tripoli,P.O.B. 417, tel: 5715, tgm: gultracoMauritiusMauritius Trading Co. Ltd. PortLouis, P.O.B. 201, tgm:agentouMoroccoElmar S. A. —SEYRE Tangier,Francisco Vitoria, 4, tel: 122-20,tgm: elmarIstanbul,Han, Kattel: 22 81 .„, .• AFRICA•Egypt (UAR)Telefonaktiebolaget LM Ericsson,Egypt Branch Cairo, P. O. B. 126,tel: 436 84, 505 53, tgm: ellemeNorthern and Southern Rhodesia,NyasalandLM EricssonTelephoneCo. (Pty.)Ltd. (Branch Office of LM EricssonTelephone Co. Pty. Ltd. in Johannesburg)Salisbury, SouthernRhodesia, P.O.B. 2891, tel: 270 01.tgm: ericssonSouth Africa, South-WestAfricaL M Ericsson Telephone Co. Pty.Ltd. Johannesburg, Transvaal, P.O. B. 2440, tel: 33-2742, tgm:ericofonTunisiaTelefonaktiebolaget LM Ericsson,Technical Office Tunis, Boite Postale 780, tel: 240520,tgm:ericsson• AMERICA •ArgentineCla Ericsson S. A. C. I. BuenosAires, Casilla de correo 3550,tel:33 20 71, tgm: ericssonCia Argentina de Tel^fonos S. A.Buenos Aires, Peru 263, tel:30 50 11, tgm: catelCfa Entrerriana de TelefonosS. A. Buenos Aires, Peru 263, tel:30 5011, tgm: catelIndustrias Electricas de QuilmeiS. A. Quilmes FCNGR, 12 de Octubre1090, tel: 203-2775, tgm:indelqui-buenosairesBrazilEricsson do Brasil Come>cio eIndustria S. A. Rio de Janeiro,C. P. 3601, tel: 43-0990, tgm:ericssonCanadaLM Ericsson Ltd. Montreal 9, P.Q.,2300 Laurentian Boulevard, Cityof St. Laurent, tel: 331—3310,tgm: canericToronto 18, Ont., P. O. B. 161,tel: BE 1-1306MozambiqueJ. Martins Marques LourencoMarques, P. O. B. 456, tel: 5953,tgm: tinsmarquesNigeriaI.P.T.C. (West Africa) Ltd. Lagos,P.O.B. 2037, tel: 26531, tgm:consultSudanVietnamTECOMA Technical ConsultingVo Tuyen Dien-Thoai Viet-Nam, and Machinery Co. Ltd. Khartoum,P.O.B. 866, tel: 2224, ext.Saigon, 34 Dai-lo Thong-Nhut,tel: 20805, tgm: telerad35, tgm: sutecomaAMERICA•BoliviaJohansson & Cla, S. A. La Paz,Casilla 678, tel: 2700, tgm: JohanssonCosta RicaTropical Commission Co. Ltd. SanJosi, Apartado 661, tel: 3432,tgm: trocoCuracao N. W, I.S. E. L. Maduro & Sons, Inc.Curocao, P. O. B. 172, tel: 1200,tgm: madurosons-willemstadDominican RepublicGarcia & Gautier, C. por A.Son/o Domingo, Apartado 771,tel: 3645, tgm: gartierGuatemalaNils Pira Ciudad de Guatemala,Apartado 36, tel: 62258, tgm;nilspira-guaternalaHondurasQuinch6n Leon y Cla Tegucigalpa,Apartado 85, tel: 1229,tgm: quin~"JamaicaMorris E.354, tel825 55, tgm: encsson-santiage.dechileColombiaCla Ericsson Ltda. Bogotd, ApartadoAereo 4052, tel: 41-11-00tgm: ericssonEcuadorTeleionos Ericsson C. A. QuitsCasilla 2138, tel: 16100, tgm:ericssonGuayaquil, Casilla 376, tel; 16892tgm: ericssonMexicoTelefonos Ericsson S. A. MexicoD.F., Apartado9958, tel: 464640,tgm: coericIndustria de Telecomunicaci6nS.A. de C.V. Mexico 6, D.F. Lond- !res No. 47, tel: 250405, tgm: in- 1dustelPeruCla Ericsson S. A. Lima, Apartado2982, tel: 34941, tgm: ericsjon !Soc. Telef6nica del Peru, S. A. IArequipa, Apartado 112, tel: 6060, •tgm: telefonicaUruguayCla Ericsson S. A. Montevideo,Casilla de Correo 575, tel: 9-26.11, tgm : ericssonUSAThe Ericsson Corporation New IYork 17, N. v „ 100 Park Avenue, }tel: Murray Hill 5-4030. 1gm:erictelNorth Electric Co. Ga/ion, Ohio,P. O. B. 417, tel: Howard 8-2420,tgm: northphone-galionohioVenezuelaCla An6nima Ericsson Caracat,Apartado 3548, tel: 543121, tgm:ericssonTelefonos Ericsson C. A. Corocos,Apartado 3548, tel: 543121, tgm:tevela• AUSTRALIA & OCEANIA •AustraliaL M Ericsson Telephone Co. Pty.Ltd. Melbourne C 1 {Victoria), 20Collins Street, tel: 635646, tgm:ericmelL M Ericsson Trimax Pty. Ltd.Coburg N 13 (Victoria), P.O.B. 2,tel: 35 1203, tgm: trimaxNicaraguaEdmundo Tefel Managua, D.N.,Apartado Postal 24, tel: 3401,tgm: edfalcoPanamaProductos Mundiales, S. A, Panama,R. P., P. O. B. 4349, tel:3-0476, tgm: mundiParaguayS. A. Comercial e Industrial H.Petersen Asuncidn, Casilla 592,tel: 9868, tgm: pargtradePuerto RicoSplendid Inc. San Juan, P. O. B.4568, tel: 3-4095, tgm: splendidEl SalvadorDada-Dada & Co. San Salvador,Aparlado 274, tel: 4860, tgm:dadaSurinamC. Kersten & Co. N. V. Paramaribo,P. O. B. 1808, tel: 4444,tgm: kerstenTrinidad, W. I.Leon J Ache - Ltd. Port-of-Spain,100 Frederick Street, tel: 32357,tgm: achegramUSAClark Walter Corporation Ntwark2, N. J., 744 Broad Street,tel: Mitchell 3-7333, tgm: wirewalter-newarknj.(For intercom)Slate Labs. Inc. New York 3, N. Y.,215 Park Avenue South, tel: Oregon7-8400, tgm: statelabs (Forelectron tubes)• AUSTRALIA & OCEANIA.