The American Monthly Review of Reviews, August, 1904, pages 191-197:
WIRELESS TELEGRAPHY TO-DAY.
BY WILLIAM MAVER, JR.
(Member of the American Institute of Electrical Engineers, and author of "Wireless Telegraphy, Theory and Practice.")
IT is now more than ten years since the successful transmission of intelligence to a distance by electric waves without wires was first announced by Marconi. Prior to Marconi's work several practical attempts had been made to transmit intelligence to a distance by means of electro-magnetic waves without the aid of connecting wires between the sending and the receiving stations, its chief application at that time being to afford a method of communicating with moving trains. A number of such systems were in actual operation on railroad lines in this country. These were termed induction telegraph systems. There was, however, no great demand for telegraph systems of this nature, and they gradually went out of existence. Sir William H. Preece, on the other side of the Atlantic, also experimented on a larger scale with induction telegraphy between lighthouses on islands and stations on the mainland, with some success, but the distances traversed did not much exceed four or five miles.
These induction telegraph systems employed in their operation the well-known principle that when an electric current is varied in one wire it induces a current of electricity in a neighboring parallel wire. In Preece's experiments, a wire several miles in length was strung on poles along the coast of the mainland, and a parallel wire was placed on poles on the island. By having a battery and key in one of the wires and a telephone receiver in the other, it was possible to transmit and receive Morse telegraph signals across the intervening space. In these induction telegraph systems, the frequency of the electric pulsations employed ranged from thirty to forty per second.
In the transmission of signals by modern wireless telegraphy, the electric vibrations or waves radiated into free space are of an immensely higher order, varying from several hundreds of thousands to many millions per second.
WIRELESS TELEGRAPH APPARATUS AND OPERATION.
As all the world now knows, the apparatus required for the operation of this wireless telegraphy is a generator for setting up the electric oscillations in a vertical wire, or antenna, as it is called, from which the electric waves are radiated into free space, together with a vertical wire at a receiving station, which intercepts and absorbs some of the electric waves which are transformed into electric oscillations in that wire, where they are detected by a receiver of electric oscillations. The received oscillations are obviously very weak as compared with the oscillations in the transmitting wire, but by employing very sensitive detectors of such oscillations the signals transmitted may be received at a great distance from their source.
In the operation of wireless telegraphy in its simplest form, electric oscillations are established in a vertical wire by an induction coil, in the primary circuit of which a telegraph key is introduced. While the key is held passive, a continuous train of electric oscillations is maintained in the vertical wire, and consequently a corresponding train of electric waves is radiated therefrom, but when the key is opened the oscillations and the waves cease. Hence, by opening and closing the key as an ordinary Morse telegraph key is operated, the train of waves is broken up into what correspond to dots and dashes of the telegraph code, and may be received as such at the receiving station.
To obtain successful wireless telegraphy, much depends on the generator of the oscillations, the height and arrangement of the vertical wires, and the sensitiveness and reliability of the wave-detector. The first generators of electric oscillations employed in wireless telegraphy consisted of the ordinary Ruhmkorff, or induction, coil, which developed about one-fifteenth of a horse-power (see illustration, fig. 1). The secondary wire of the induction coil is connected with the vertical wire, which it charges with electricity until the air at the spark gap breaks down, whereupon electric oscillations surge back and forth in the vertical wire, radiating electric waves in the ether. The detector of the radiated waves employed by Marconi was a modification of what is known as the filings coherer, the operation of which is due to the fact, discovered by Dr. Branly, that metal filings when thrown loosely together and made part of an electric circuit have a normally high electrical resistance, but in the presence or under the influence of electrical oscillations this resistance vanishes and they become conductors of an electric current. It was assumed that the electric oscillations cause the filings to cohere more closely together, thereby making a better contact with one another, hence the term coherer as applied to this form of electric-wave detector. It was further noticed that when the filings had thus cohered they retained their electrical conducting property even after the cessation of the oscillations until they were tapped or otherwise jarred, whereupon they resumed their normal high-resistance condition. Therefore, to make this device operative, a means of jarring the filings continuously to restore them to normal condition was necessary, and this was easily found in the shape of a vibrating bell, the hammer of which was caused to tap the tube containing the filings (see fig. 2).
DEVELOPMENT OF THE DETECTOR.
The speed of signaling with the "tapping backs" coherer is inherently slow, probably from eight to twelve words per minute, and the instrument is also more or less unreliable, requiring frequent and careful adjustment. Hence, it was evident to all concerned in the advancement of wireless telegraphy that the production was desirable of a detector more sensitive and more reliable than the filings coherer, and one which upon the cessation of the oscillations in its circuit would at once automatically resume its normal condition. A number of detectors capable of fulfilling these requirements have been devised in the past five years, among them the Solari mercury autocoherer, used by the Italian navy; the Marconi and other magnetic detectors; the De Forest electrolytic detector; the Fessenden "heat" detector, and the Lodge-Muirhead oil-film detector. Each of these electric-wave detectors, or, more correctly, electric-oscillation detectors, while differing more or less in principle, effect the same final result,--that is, they either produce or vary a current in a local circuit in which is placed a telegraph relay or a telephone receiver, or they vary the resistance of that circuit and thus cause the relay or telephone to respond to the received signals.
At the present time, almost every civilized nation has developed one or more systems of wireless telegraphy. In the United States there are the De Forest and Fessenden systems; in Great Britain, the Marconi and Lodge-Muirhead systems; in Germany, the Slaby-Arco and the Braun systems, which are now consolidated under the name of the Siemens-Halske wireless system; in France, the Ducretel and other systems. Italy, naturally, also claims the Marconi wireless method. In Russia, the Popoff system is used; while in Japan a wireless system has been developed the inventor or inventors of which are not definitely known.*
IN ALMOST UNIVERSAL USE.
It is difficult to ascertain the actual degree of perfection to which several of these systems have been brought, owing to the varying statements that reach the public. But enough is known to make it clear that for distances ranging from twenty-five to two hundred and fifty miles over water wireless telegraphy is now fairly reliable for commercial business and other purposes. Wireless systems are now installed on a large number of ocean-going steamers, with results that are admitted to be fairly satisfactory. Numerous circuits are in operation between the mainland and lighthouses in this country and Europe, where messages to and from passing vessels equipped with wireless systems are regularly exchanged. The important war vessels of every navy are now equipped, or are being equipped, with wireless outfits; the British Government, for example, is expending about one hundred thousand dollars per annum for this purpose. The military authorities of the world are also utilizing this system to the utmost by the equipment of forts with the most practicable systems procurable. Wireless outfits are also made a part of the signaling system for land operations, for which purpose the apparatus is carried in two carts, on one of which is usually placed an oil engine which operates an alternating current generator. The transmitting and the receiving apparatus are carried on the other cart. As the masts used to support the vertical wires at fixed stations weigh from four to six tons, and therefore are not readily portable, small balloons charged with hydrogen are used in ordinary weather to uphold the vertical wires. In stormy weather, the wires are supported by four or six kites.
ITS MOST PRACTICAL USE.
It has long been pointed out that one of the most practical uses of wireless telegraphy commercially is between places divided by the ocean where it is not feasible to lay a cable, either on account of the expense involved because of the rocky nature of the shore, which would speedily chafe and destroy a cable. A notable example of this use of wireless telegraphy is the recent installation of a De Forest wireless circuit between Boca del Toro, Panama, and Port Limon, Costa Rica, for the convenience of the fruit-growers and merchants of that neighborhood. The distance between these points is seventy miles, and the service has been satisfactory from the start. In a number of instances the ability to communicate between the fruit-grower and the shipper at critical times has resulted in the saving of many thousands of dollars. The masts supporting the vertical wires and the interior of the station at Port Limon, are shown in the accompanying illustrations. In the interior picture, the Leyden jars, or condensers, and the spiral wire, or inductance coil, of the oscillating circuit are shown at the far end of the table. The wireless receiving apparatus, including the De Forest electrolytic receiver and the head telephone, are shown on the rear end of the table. A commercial telephone set, for ordinary telephone use, is shown at the left side of the table. It will be understood that the head telephones of the wireless outfit are used for the reception of the Morse signals, which are heard as long and short sounds in the receiver. There is no reasonable doubt that there are numerous other places where a similarly valuable use of wireless telegraphy could be made. In addition to examples of this kind, there have also been numerous occasions upon which wireless telegraphy has been employed to great advantage by vessels requiring assistance, and such instances will multiply as the use of this system increases.
WIRELESS TELEGRAPHY IN THE FAR EAST.
The recent successful employment of wireless telegraphy in the far East in affording a means of communication from the beleaguered Port Arthur, and especially in the transmission of war news from the war zone, has renewed attention to its potential utility. It is known that a wireless station was established at Golden Hill, at least as long ago as the spring of 1903; for regular communication between Port Arthur and the Russian warships in the Gulf of Pe-chi-li. In the waters of the far East there are at least five different systems of wireless telegraphy on the various warships and in the forts. The British have more than twenty vessels in those waters equipped with the Marconi system in which the filings coherer is used. The Italians, also, employ the Marconi system with the Solari coherer. The Germans are using the Slaby-Arco or the Braun system. The French vessels are probably equipped with the Braun system. The Japanese are employing a system which, it is asserted, is a modification of Marconi's; but this is denied by the Japanese. It is known that wireless experiments have been carried on by the Japanese Department of Communications and the Japanese navy since 1896.
SOME DIFFICULTIES.
When it is considered that all of these vessels and stations are endeavoring to use the ether for signaling purposes at one time, it is evident that, unless it be possible to cut out, or in some way to eliminate, the effects of the signals of outsiders, more or less confusion must result. For instance, at the time of the British naval maneuvers in 1903, it was stated by a newspaper correspondent that, owing to the "interference" of one set of signals with the other, both sides ceased to pay any attention to the disjointed messages; hence, the wireless system was of no use to either side.
This question of interference is obviously a very important one, since if it can be successfully carried out in warfare it renders nugatory any attempt of the belligerents to carry on communication by its means. The same statement may be made with regard to commercial wireless telegraphy.
CAN "INTERFERENCE" BE REMEDIED?
It is, however, measurably true that by an arrangement of the wireless circuits termed tuning a system can be so adjusted that it will respond to but one set of waves, regardless of how many other sets may be passing. An understanding of the manner in which this result is effected may be gathered by considering the manner in which a practically similar result is obtained by mechanical means in a wire telegraph method known as harmonic telegraphy. In this system, three or four forks attuned to different notes, and consequently to different rates of vibration, are so placed in a telegraph circuit that they set up current pulsations in that circuit corresponding to their fundamental rate of vibration. The pulsations set up by each of these forks are controlled by telegraph keys. At the receiving station, four ordinary electro-magnets are placed in the circuit. The armatures of these magnets consist of tuning-forks each of which is attuned to vibrate at a rate corresponding to that of one of the transmitting forks, and it will respond only to the pulsations of current set up by that particular transmitting fork. Hence, it is possible by these means to send four, or even more, separate messages over one telegraph circuit.
In an analogous way, the attempt is made, more or less successfully, in wireless telegraphy, to tune the respective systems so that each will only respond to a given set of electric waves in the ether. It is not possible to employ in wireless telegraphy the mechanical method of tuning just described, but it is found possible to tune the oscillating circuits at the transmitting and receiving ends by electrical means. This is done by taking advantage of the fact that the rate or frequency of electric oscillations in a circuit is governed by the resistance, the capacity, and the inductance of the circuit, which properties of an electric circuit may be likened to friction, elasticity, and inertia in mechanics.
In actual practice, however, while fairly successful results have been obtained by tuning the oscillating circuits, it has not hitherto been found feasible to entirely prevent or cut out interference between different systems if the interfering waves are of sufficient strength, especially if the oscillations are approximately of the same order or frequency. When, on the other hand, the rate of oscillation employed by different stations is quite dissimilar, attempts to cut out interference are much more successful.
But it is a fortunate fact that when the telephone is used as a receiver in wireless telegraphy it is not absolutely necessary to success that the signals of other stations shall be cut out altogether. It suffices if by tuning or distance the interference is minimized. In such a case, the signals intended for a given station may be read by an expert operator, while the extraneous sounds are disregarded, in virtually the same manner, for instance, as when a number of people are conversing at one time in a room a listener may select the conversation of any one speaker in the room and hear him to the exclusion of all the other speakers, notwithstanding that the sounds of all the voices are falling upon the tympanum of the listener's ear.
EXTENSIVE USE IN ORIENTAL WATERS.
According to advices from the operators of the De Forest wireless system in Chinese and Japanese waters, there is an unending train of wireless signals going on day and night in that vicinity. The signals of the Russians and the Japanese, and especially of the latter, can be heard at all hours, these nations, in common with all others, using in telegraphy a modification of the Morse telegraph alphabet. The telegraph alphabet used by the Russians contains thirty characters; that of the Japanese is said to contain forty characters, while the American Morse contains but twenty-six characters. But, apart from this difference in the alphabets, the belligerents use cipher codes which render their communications unintelligible to outsiders, even if they were otherwise readable.
The De Forest wireless station in North China from which the wireless war news is cabled to Europe is situated on a cliff somewhat east of Wei-Hai-Wei. The height of the vertical wire used is about one hundred and fifty feet, which is also the height of the station above sea level. The Chinese steamship Haimun, which was chartered by the London Times for news-gathering by wireless telegraphy, has a vertical wire about ninety-six feet high. The transmitting and receiving apparatus employed at Wei-Hai-Wei and on the Haimun are practically identical, and the operating-rooms virtually correspond to those of the Panama and Port Limon stations. Messages were freely sent to and from the boat at distances ranging from ten to one hundred and fifty miles. The signals could be heard at greater distances from the boat to the shore than contrariwise, the rolling of the boat at times interfering with the reception of signals. At the time of Russia's announcement that correspondents employing wireless telegraphy in the war zone would be treated as spies, the Haimun was on the Korean coast and those on board were promptly informed of the interesting situation by wireless telegraphy.
EXCELLENT SERVICE TO THE "HAIMUN."
This vessel has had several interesting experiences. One day last April, when the Haimun was within twelve miles of Port Arthur and eighty-five miles from Wei-Hai-Wei, on the look-out for war news, she was held up by a shot across her bows from the Russian warship Bayan. Not knowing what might happen, Captain James, the correspondent of the London Times on the Haimun, sent a wireless dispatch to Wei-Hai-Wei, notifying that station that they were about to be boarded by officers of the Russian battleship Bayan. "If you do not hear from us in three hours," said the message, "notify commissioner, captain of British gunboat Leviathan, and London Times." There was some natural anxiety to know if the message had been received, but presently all anxiety was relieved by the welcome signal "O. K." from the Wei-Hai-Wei operator. In a short time a reply came stating that the commissioner and the commander of the British fleet at Wei-Hai-Wei had been properly notified, and that from the window of the operating-room it could be seen that the fleet was getting up steam,-- "and that," added the operator, "is no dream." Two Russian officers boarded the Haimun, inspected the wireless apparatus, and took a copy of the last message sent. In the midst of their inspection, the officers were hurriedly recalled to the Bayan by apparently excited signals from that ship, which immediately returned to Port Arthur. It was surmised by those on the Haimun, as an explanation of their hasty return, that the Russians had detected Japanese wireless signals. On the other hand, it is quite possible that the Bayan's wireless operator may also have received the messages sent from the Haimun and from Wei-Hai-Wei relative to the boarding of the Haimun, and this, for prudential reasons, may have occasioned the hasty recall of the boarding officers. On this point it may be noted that while the ether itself transmits all forms of electric waves impartially, it is quite within the probabilities that some characteristic in the method of transmission, or some peculiarity of code used by one vessel or fleet, might after a little experience be quickly recognized by other fleets, and in this way the presence of friend or enemy could be recognized without a regular message.
AN INTERNATIONAL AGREEMENT.
The fact that the operation of powerful wireless coast stations has been found to seriously interfere with the operation of wireless telegraph systems on shipboard has already led to protests from maritime interests, in various countries against the indiscriminate extension of such powerful stations. It is manifest that ordinary steamships or sailing vessels, and lightships and lighthouses, cannot maintain powerful installations, nor can they command the services of experts to manipulate wireless tuning apparatus to minimize or eliminate interference. Furthermore, the attunement of wireless systems on shipboard or on lighthouses to one or more set of electric waves is obviously not desirable, inasmuch as in case of need these vessels and stations should be able to interchange communication with any system within their influence.
An international wireless telegraphy conference was held in Berlin last summer for the consideration of matters of the nature just mentioned, and of others analogous thereto, and a number of rules were adopted for the proper regulation of wireless telegraph operations in the best interests of all concerned.
ACTION BY THE UNITED STATES GOVERNMENT.
It has recently been reported that the United States Government has under consideration the advisability of obtaining, by Congressional enactment or otherwise, the exclusive control of all wireless telegraph stations on the coasts of this country, on the ground that only in this way can the coast be properly defended in time of war, so far as wireless telegraphy may be useful to that end. In no other way, it is intimated, can interference between conflicting wireless stations be prevented and the proper control and systemization of the wireless service be successfully brought about. At the present time, at least four different wireless systems are employed by various departments of the United States Government,--namely, the Slaby-Arco, by the navy department; the Braun system, by the army, for land operations; the Wildman system, by the Signal Corps of the army, and the Fessenden system, or a modification of that system, by the Weather Bureau. The Wildman system is understood to be a combination, with improvements by Captain Wildman.
It would certainly seem desirable that a standard system should be adopted for all branches of the Government, in order, if for nothing else, that a ready interchange of men and apparatus might be feasible. Under existing conditions this is evidently not the case. To determine in what manner the foregoing results may best be obtained, and to consider the subject in all its bearings, the President has appointed a board consisting of representatives of the army and navy, whose findings, it is intimated, will shortly be reported. In the meantime, the Government has entered into a contract with one of the existing wireless telegraph companies for the establishment of a series of five wireless telegraph circuits, namely, between Key West and Panama, a distance of one thousand miles; Key West and Pensacola, four hundred and fifty miles; Porto Rico and Key West, one thousand miles; southern Cuban coast to Panama, seven hundred and twenty miles, and southern Cuba to Porto Rico, six hundred miles. The ultimate object of these proposed stations is, it is stated, to provide an alternative method of communication, in case of emergency, with the government's outlying territories and interests in Central America, and possibly in the far East. The masts for these stations will be from two hundred to three hundred feet in height, and the power of the generators of the electric will probably range from twenty-five to forty horse-power. Inasmuch as the height of the wires hitherto employed has not much exceeded one hundred and fifty feet, and the power employed at the generator has been from two to three horse-power, with which distances of from one hundred and fifty to two hundred miles have been reached, it is expected that the additional height of the vertical wires and the greatly increased power will make it possible to transmit messages over the much longer circuits. This, however, remains to be determined.
At present, it may be remarked that the United States Government is alone in not possessing a monopoly of wireless telegraphy on its coasts and within its boundaries. In Great Britain, the government declined to give the Marconi system certain desired privileges unless it would guarantee that the more powerful stations would not interfere with existing wireless stations of the British Admiralty. In France, a wireless station which was erected at Cape La Hogue without governmental authority was, it is reported, "seized" by the police. Germany, Italy, Russia, and other European nations also exercise complete control over wireless telegraph systems, while in far-off Ceylon a fee is exacted for the operation of such circuits on that island.
__________
* For full details of these systems, and of the apparatus employed in their operation, a description of which would be beyond the scope of a magazine article, the reader may be referred to the author's works, "Wireless Telegraphy, Theory and Practice," and "American Telegraphy and Encyclopedia of the Telegraph."