Popular Science Monthly, November, 1918, pages 149, 151-153:
A New Wireless Chain Between the Americas
By John V. L. Hogan
IT has long been the ambitious dream of wireless men to supplement the present cable systems between the North and South American continents by means of a chain of high-powered radio-telegraph stations. Difficulties in securing concessions and capital, and (by no means least) apparatus capable of working continuously and dependably over great stretches of land and sea, have invariably interfered with the completion of the projected Pan-American systems. At least, if the announcements issued through the press are to be relied upon, some or all of these handicaps have been overcome and the connection of New York and Buenos Aires by wireless will become a fact toward the close of the current year.
A new corporation, called the Pan-American Wireless Telegraph and Telephone Company, has been organized to make use of the Marconi and Poulsen patented systems in a group of powerful plants which will interlink the most important points in the American continents. Concessions which the English Marconi Company and the Federal Holdings Company (which formerly controlled the Poulsen patents in their relation to Pan-American work) had secured are reported to have been turned over to the new company. It is generally understood that the first work will be to complete the pair of stations for transmitting messages directly between New York and Buenos Aires which were undertaken and announced by the Federal Company some years ago but on which practically nothing other than the preliminary surveys was done. The Pan-American Company has not disclosed its plans for the location of the first station in the United States, but the Federal Company stated that their Northern station would be placed on the coast of Long Island some forty miles from New York. It seems likely that, instead of putting up a new installation, the Pan-American Company will utilize one of the Marconi plants (at New Brunswick, N. J. and Chatham, Mass.) which were erected for trans-Atlantic communication three or four years ago, but which have never been used.
"Damped" and "Undamped" Wireless Systems
The fact that the Poulsen patents are taken over in connection with those of Marconi, implies that the new installations will use the continuous wave system of wireless telegraphy, since the Poulsen arc transmitter produces radiation of the "undamped" or continuous type. There are, broadly speaking, two classes of wireless or radio transmission, viz., the "damped wave" and the "continuous wave." The former has been advocated by the Marconi interests for many years, and is characterized by the production of wireless waves in groups separated by intervals of idle time. The continuous wave system, as its name indicates, sends out the wireless waves in an unbroken stream and so uses all of the apparatus all of the time. This system, which the courts have decided was first proposed by Fessenden, has been found by experience to be far more effective than that using damped waves. It is much used by both the enemy and our allied governments in the great war, and forms the basis of the large and successful trans-Atlantic stations at Sayville and Tuckerton in the United States.
The Marconi stations have all been fitted with spark (damped wave) apparatus. However, experiments with instruments for generating continuous waves are stated to have been in progress for some time at the more important points, and the newer generators will doubtless be substituted for the spark type (which is now considered obsolete for sending messages over extremely long distances). Thus the new plants for Pan-American service may be expected to radiate waves in a continuous stream instead of in short, separated groups. The increase in effectiveness is much like that found when one puts out a fire by turning a hose upon it instead of attempting to do so by throwing water with a teacup.
A Typical Long-Distance Station
The inauguration of a new service over such extreme distance as the 4,000 miles which separate New York and Buenos Aires, is no small undertaking, and to establish commercial communication before the end of 1918 (which is the schedule announced) will be a remarkable feat. Some idea of the enormous quantity of detail involved may be secured from Fig. 1, which shows the plan of a typical trans-oceanic wireless operating and receiving station. This building is located at some distance from another which contains the powerful sending apparatus, so that the strong electrical disturbances created at the transmitter will not interfere with the receivers. Since the actual Morse operating must be concentrated for effective work, the house shown contains the sending keys as well as the apparatus for reception. This location of the sending control of course, necessitates wire line connections between the operating building shown and that containing the sending plant.
In the diagram, A represents telegraph and telephone lines connecting the wireless station with the outside world. Messages for transmission to South America arrive over these lines, and, passing through the switchboard and power room B, reach the receiving telegraph operator at desk C. Here the operator copies the dispatch upon a blank form and places it upon a traveling endless-belt carrier which runs along the rear of the desks from C to H, through the dividing walls shown. A second receiving desk is provided at D, so that in case of an overload of incoming messages an additional operator may be placed on duty to aid in relieving the congestion.
The written incoming message passes into the radio room in the center, and is automatically lifted off the bolt conveyor at the desk E, where the sending radio-operator is stationed. Here he works the key which controls the main radio sender by means of automatic switches in the power room B, connected over the lines I which run to the transmitting apparatus house. Duplicate apparatus and lines must be provided, so that a breakdown will not interrupt the service. On the table behind the sending desk E is installed an automatic tape transmitter, which is used to send out long press dispatches and deferred service radiograms. So much for the route of an outgoing wireless message,--the key on the desk E controls the big sending plant, so that once a word of the written message is formed in Morse characters by the operator there, it is immediately transformed into the dots and dashes of radio waves which speed off into space and reach the South American station a fraction of a second later.
How Incoming Messages Are Handled
Considering the reverse routing, messages which arrive from Buenos Aires as wireless waves strike the aerial wires at the North American station, and are converted into feeble high frequency alternating currents. These currents pass into the radio room by way of the leading-in wire I of Fig. 1. The wires I are connected to the receiving instruments on desk F; and the operator there listens to the dots and dashes, writing out the messages and placing the blanks upon the belt conveyor which takes them into the next room to the right. At F is installed a duplicate receiver for use in case of emergency or whenever it is desired to receive simultaneously from two distant radio stations.
The desks G and H in the next room are used for outgoing wire lines, over which the received radio messages are distributed throughout the United States. The room J is a small laboratory and shop, for adjustment of instruments and such minor repairs as are often required. The main traffic office is represented by K where the clerical work of the station is carried on and where the perforated tapes for the automatic transmitters are prepared upon special keyboard machines resembling typewriters. The power room B contains the switchboards for distributing the various telegraph wires to the desks desired. the motor-generators for converting power to the voltages needed for telegraph work, the relays, magnetic switches and other larger apparatus whose operation might disturb the telegraphers. The reason for locating the sending and receiving desks together in the radio room is that thus the receiving operator may at any moment interrupt the sending of outgoing radio messages to secure a repetition or confirmation of any obscure letters or words in an incoming dispatch. It is apparent that, with a station arrangement of this character, messages are simultaneously in transit In both directions, in other words, the wireless is "duplexed."
Duplex or double operation is much facilitated by the use of continuous waves, and only moderate separation of the sending and operating houses is required. With some special devices they may be only a few hundred yards apart, or even in the same large building.
The Receiver of the Poulsen System
The wireless receiver of the Poulsen system is the so-called "tikker," which is shown at S in Fig. 2. This diagram shows how the serial wires M are connected through the tuning coils N and O to the ground at P. It is through these wires and coils that the high frequency currents flow. A secondary coil Q and tuning condenser R are associated with the antenna circuit coils, and from the condenser wires lead to the "tikker" S, a telephone T and a telephone condenser U. The "tikker" is merely a rapid interrupter of any one of several forms, which serves to make the wireless signals audible to the operator who listens in the telephone receiver T. This "tikker" receiver was first put out some ten years ago, and has had extensive use. It is now largely supplanted by other more effective devices, one of which will doubtless be used in the Pan-American stations.
The Poulsen Arc Sender
A typical sender of the Poulsen undamped wave system is shown in Fig. 3, where the electrical power comes in over the power lines PL and goes to the motor generator MG, which produces the high voltage direct current needed. This current passes through the windings of two powerful electromagnets, N' and S', to the arc A', which is the most important element of the system. The arc has one electrode of copper and the other of carbon, and burns between the two magnet poles in an atmosphere of hydrogen gas. The carbon electrode is normally connected to ground G', and the copper to the aerial wires AW through a tuning coil TA. The unusual property of such an assembly is that the arc, when properly adjusted, converts the applied direct current into radio frequency alternating current suitable for wireless transmission. The waves of the frequency desired for sending are turned off and on by the magnetic switch or relay R', which is controlled from the desk E (Fig. 1) over the wire lines I.
Although the details may be altered a great deal without changing the general plan, the modern long distance wireless station is well typified by the above illustrative installation. The new Pan-American Company has not announced the exact arrangements which it proposes to use, but in principle they are not likely to depart very far from those just outlined. The radio profession, as well as the business world, is interested in watching this newest great wireless project; and only good wishes and encouragement are to be extended toward the men who now attempt to interlink more closely the two American continents.