Telephonic communication is now possible between London and almost every country in the world. A vast network of wore and radio links is controlled from Faraday Building, London, which has become the nerve-centre of world communication
RADIOTELEPHONY SWITCHBOARD at Faraday Building, London, with which the great transmitters at Rugby are connected. The row of names above the switchboard is a testimony to the enormous range of the modern telephone system. On the left is a double stopwatch used for timing the conversations: one of the watches is stopped during periods of interference.
FARADAY Building, in Queen Victoria Street, is one of London’s newer landmarks. Eleven stories in height, it is also one of London’s highest buildings. Such prominence befits a building which, by day and night, all the year round, is in telephonic communication with almost every corner of the world, and with ships on the high seas.
This building is, by its position and purpose, the telephone centre of Great Britain, of the British Empire and of the greater part of the world. From Faraday Building and its sister building in Carter Lane wire and wireless links radiate in every direction, and inside the buildings a maze of complicated apparatus embodies everything that human ingenuity and engineering skill have been able to devise in perfecting the telephone. Faraday Building may be regarded as the counterpart of the Central Telegraph Office; it is to the telephone what the C.T.O. is to the telegram. Inland telephones, however, are handled through local exchanges in many instances, so that Faraday Building has become the home of long-distance telephony.
As inland trunk calls are dealt with in a manner similar to that in which toll calls are handled (see the chapter “Modern Telephone Exhanges”), it is the purpose of this chapter to deal with Continental and overseas telephony, which is managed by “International Exchange” — surely one of the most marvellous rooms in the world.
The Continental Exchange, as its name implies, provides communication between Great Britain and important centres on the Continent of Europe. Some 140 direct circuits radiate from this exchange, connecting it with every country in Europe as well as with such islands as Corsica and Sardinia in the Mediterranean Sea.
These outgoing lines are brought to terminal points on control panels, which are multiplied to whatever extent may be justified by the importance of the circuit. For instance, Paris lines are handled by a larger number of operators than any others. Continental calls are handled in a way that differs little from that which is used for ordinary inland calls.
When a call arrives from such a centre as Paris it is visually shown by a light on the switchboard, and this light is multiplied on all the switchboards working with Paris. As soon as,it has attracted the attention of a free operator, who inserts a plug in the appropriate socket, the light — on all the switchboards — disappears, thus indicating to all the operators that the call has been dealt with. Calls from British subscribers are received on switchboards at a large central table. Their demands are noted and instantly recorded on a ticket. This ticket is “posted” through a slot which drops it on to a concealed band conveyer, and this conveyer takes it swiftly to a sorting position. From this position the ticket is inserted in a pneumatic tube conveyer which delivers it, in a few seconds, to one of the operators who deal with outgoing calls.
As soon as a circuit on the particular route required is free, an operator calls the distant exchange and asks for the Continental subscriber concerned. While this subscriber is being obtained, the local subscriber is called again, and finally connexion is completed.
An intricate and interesting system is in use for determining the delay that is likely to occur before the connexion can be made. An operator keeps watch on the amount of traffic being handled by each circuit, and sets indicators in accordance with these observations. These indicators are connected to press-buttons in front of all the operators who deal with incoming calls. When a
request for connexion with some Continental centre is received, the operator answering the subscriber simply presses the appropriate button, and by a coloured light code is immediately informed of the delay that is likely to occur. All information relating to payment for the call is recorded on the tickets, which are filled in for every call. There is also an interesting visual arrangement for showing the operator how long a call has been in progress. The same mechanism operates the “pips” which warn the subscriber that a certain time interval has elapsed.
Coloured strips face the operator at the switchboard, and when one minute has elapsed the figure 1, at the left-hand end of the strip, is illuminated by a bulb behind it. Within fifteen seconds of the completion of two minutes the figure 1 begins to “wink”, until finally it is extinguished and replaced by the figure 2 in an adjacent space. The last few vibrations are transmitted along the line in the form of an audible signal — the “pips”.
The timing device is automatically cut out of circuit and stopped when the calling subscriber replaces his receiver at the end of a call, and the length of the call — to the nearest minute — is recorded on the slip which carries all particulars concerning the call.
The operators sit in rows in front of long, orderly switchboards, each of them a maze of switches, sockets and light signals, and each bearing above it the name of the Continental centre at the far end of the line. To stand in this room and to read off “Moscow—Stockholm—Rome—Copenhagen—Oslo —Prague—Budapest—Vienna” is an experience that brings home, in no uncertain fashion, the wonders and the completeness of the modern telephone system.
Long-distance cable calls, however, involve the use of so much apparatus that all this complicated array at the exchange represents only an extremely small part of the whole. The London switchboard is connected with the distant point by a circuit consisting of two pairs of wires, one of which carries the speech current in one direction, and the other in the reverse direction.
TERMINAL CONTROL POSITIONS in London, where the outgoing speech from a telephone subscriber is “scrambled’’ or made unintelligible before being passed over the wire link to Rugby radio station. The same apparatus “unscrambles’’ incoming speech. Much intricate apparatus is used for the amplifying and “matching’’ of outgoing and incoming telephony.
For a connexion between London and Rome the circuit is some 1,300 miles long and consists of about 47 tons of copper wire, insulated with paper wrappings and enclosed for its entire length in a lead sheath. It is the thermionic valve — a device largely responsible for the development of radio during recent years — which has made long-distance cable connexions possible.
Without the aid of valve amplifiers along the route, the thickness of the copper wires necessary and the power that would be required to operate a telephone receiver in Rome would be so great as to make the service absolutely impracticable.
Every 2,000 yards along the route a device known as a loading coil is connected. The loading coil modifies the flow of current along the circuit. In addition, every fifty miles along the route there is a “repeater station” which uses a thermionic valve amplifier. On the London-Rome circuit there are twenty-seven such repeater stations — two in England, ten in France, five in Switzerland and ten in Italy. At each of these stations a skilled staff of engineers is employed for purposes of operation and maintenance.
All cables are laid underground, a submarine cable conveying the speech currents across the English Channel. The English repeater stations are at London and at Canterbury, Kent, the next amplification taking place at Boulogne, France — at the far end of the submarine cable.
If the Continental Exchange is wonderful, then the Overseas Exchange is surely miraculous. Ever since 1876, when Graham Bell demonstrated his telephone as a commercial proposition, engineers engaged on the development of speech transmission have been striving to annihilate distance. The fruits of their labours may be seen in the Overseas Exchange, in which the names over the switchboards form a girdle round the world.
“Sydney, Rio de Janeiro, Cape town, New York, Ships, Cairo” — these are some of the distant points with which the operators are speaking in ordinary conversational tones.
Radiotelephony is used for all these overseas connexions. This exchange may be said to have been founded in January 1927, when, after prolonged and patient research by engineers of the British Post Office and of the American Telegraph and Telephone Company, the Transatlantic Radiotelephone Service was established.
This service provided, at first, a channel of communication between the ordinary telephone systems of London and New York, but it was not long before the connexions on the British side embraced the whole of Great Britain and, on the American side, the whole of the U.S.A. Thus, through the medium of a single radio channel across the Atlantic, any telephone subscriber in Great Britain could ring up any telephone subscriber in the United States.
The next step was the duplication of the radio channel as the traffic grew. Then three additional channels were opened between Great Britain and the United States. Next, radio channels were opened between Great Britain and Australia, South Africa, Canada, India, Argentina, Brazil, Egypt and ships on the North Atlantic route.
Still the network was not complete until this almost world-wide radiotelephone system had been linked up with the entire cable system of Europe. This, however, was carried out, until now there seems to be no limit to the scope of the telephone system.
Not only are the radio channels linked up with local cable systems, but they are also linked one with another in London, so that connexions may be set up between North America and Australia, or between South Africa and Japan, using London as an “international exchange” in the strictest sense of the words.
MAIN BUILDING AT RUGBY RADIO, the station which handles most of the long-distance radiotelephony calls. The 820-feet mast in the centre is one of twelve that support the long-wave aerials; most of the long-distance telephony is radiated from directional aerials, some of the supporting towers of which are seen in the background. Rugby Radio is described in the chapter “Giant of the Ether”.
All the highly complicated apparatus demanded by this marvel of modern electrical engineering is completely hidden from the switchboard operators. All that they see is the familiar control board with sockets, switches, lamps and the pairs of plugs on flexible cords. On the Overseas Exchange switchboards are terminated the British ends of all radio channels, the British ends of many of the principal Anglo-Continental cable circuits and, in addition, the London ends of some of the main inland circuits.
The terminations, as in the Continental Exchange, are multiplied over a number of switchboards so that they are instantly accessible to all the operators. When an overseas connexion is to be set up there is often much preparatory work to be done, because most of the calls are personal. Much operating in a foreign language is involved, and the time variation over different parts of the world adds to the complications.
The General Post Office transmitting station at Rugby (see the chapter “Giant of the Ether”) is used for overseas work, and the incoming transmissions are picked up at the receiving station at Baldock, Herts. These stations, however, are regarded simply as cogs in the wheel which runs the telephone system. Rugby merely supplies a carrier wave on which the outgoing speech currents are superimposed. Technical operators at Faraday Building speak directly to the technical operators at the distant end, arranging for changes of wavelength and checking the state of the circuit. The engineers at Rugby switch off one transmitter and switch on another, or change the aerial system, but they do this only in accordance with predetermined timetables or with instructions received from the great nerve-centre in London.
As secrecy is of the greatest importance in a radio transmission, which any amateur with a short-wave receiver can tune in, elaborate precautions are taken in Faraday Building. The outgoing speech is “scrambled”, or inverted, and the same apparatus as performs this operation is used for “unscrambling” the incoming speech and making it intelligible. The speech that is transmitted through the ether is completely meaningless to any one who does not have the apparatus necessary for deciphering it.
This contingency is now extremely remote, as on certain important-channels the method of making the speech unintelligible is changed every twenty seconds. The inverter is run in perfect synchronism with an exactly similar piece of apparatus at the far end. While a London subscriber is in the middle of a syllable, the method of inverting his speech may be suddenly changed, but the person listening at the distant point will know nothing about the change.
The technical operators are responsible for continual checking of the noise level and for the reliability of the various overseas circuits. Most circuits are handled on short wavelengths, and these wavelengths undergo changes of character not only at different times of the day, but also at different seasons of the year. One particular wavelength may give excellent service between London and New York from 9 a.m. till 11 a.m., but it may then begin to fade out and become unreliable. There will, however, be no hiatus in the telephone service. The engineers at either end will know what to expect, and another channel, on a different wavelength, will be open and ready for use by the time the first channel shows signs of becoming irregular in operation.
RADIO CONTROL ROOM in Faraday Building. From this room many famous worldwide broadcasts have been controlled, the Post Office providing the channels between the point where the programme originates and the broadcasting authority which is radiating it. Australia. Canada, New Zealand, India and South Africa have often been “brought together” in this control room.
Observations spread over several years have acquainted the engineers with the normal behaviour of the short wavelengths, and the choice of a channel has almost become a matter of stereotyped routine. Occasionally, however, intense magnetic storms or periods of unusual solar activity will completely upset the engineers' calculations. At such periods, which are fortunately rare, the overseas telephone service may sometimes be interrupted and become somewhat unreliable. Generally, however, the day’s log is free from the dreaded word “uncommercial”.
In fairness to the subscribers, no charge is made for periods during which conversation is difficult or impossible. Operators at the London switchboards listen to the whole conversation and make notes on a printed “Radio Service Observation Slip”. At the same time they have in front of them double stopwatches, one recording the total time spent on the call, and the other, which they stop whenever a subscriber is obviously in difficulties or is being interrupted by interference or atmospherics, recording the chargeable time.
Between the switchboards and the line to Rugby or the line from Baldock are amplifiers, speechinverting apparatus and impedance-matching apparatus, the purpose of which is to provide a proper degree of “mixing” between incoming and outgoing speech. Two separate channels are used, but the speech currents travelling along these channels are arranged so that the subscriber and the listening operators hear either end at the same strength. The radio control room is thus the connecting link between the switchboards and the transmitting or receiving station.
The flexibility of the entire system makes it possible for complex connexions of almost every kind to be established. For instance, a subscriber in Chicago, Illinois, wishes to speak to someone in Bangkok, Siam. When the connexion is finally made, his speech is transmitted along a cable from Chicago to New York, being amplified by repeater stations on the way. From New York it is passed to the radio transmitter at Rocky Point, N.Y., where it is amplified again — this time to a power which is several million times greater than that at which it arrived in New York.
From Rocky Point the speech is radiated through the ether, and the minute proportion which is picked up at Baldock, Herts, is but a fraction of the speech which was sent along the cable in America. From Baldock it comes in to International Exchange in Faraday Building. After having been suitably treated in the radio control room there, it goes out to the switchboard and is fed to a cable connexion to Berlin. More amplification takes place at repeater stations along this line. In Berlin it is turned into radio once more, and radiated through the ether to its destination, where it once more goes into a local cable system.
Paris can transmit directly to New York by radio, but in spite of this many French calls to New York come to Faraday Building by cable and are then sent to Rugby and radiated thence. Another extremely important and interesting section of Faraday Building is concerned with international broadcasting. Programmes in which all parts of the British Empire co-operate are all dealt with here. The British Post Office, with its world-wide system of telephone services, provides the channels between the point where the programme or speech originates and the broadcasting authority which is radiating it for the benefit of its listeners.
While India is talking to Great Britain, her speech is being radiated to Australia, Canada, New Zealand and South Africa, so that each may hear the cue for her part in the transmission.
AN AMPLIFIER STAGE in one of the short-wave telephony transmitters at Rugby. A telephone subscriber talking to a distant country brings into use some of the most modern radio apparatus in the world, as well as all the intricate organization of the International Exchange in London.