Wireless Telegraphy and Telephony Simply Explained

Chapter V Tuning and Coupling, Directive Wave Telegraphy.

Tuning has been mentioned in several places but not explained in any greater measure than was necessary to render a conception which would enable the reader to follow the text intelligently in order not to depart from the subjects under discussion there and consequently defeat the purpose of clearness.

The great importance and value of properly "tuning" the circuit of radiotelegraphic apparatus cannot be overestimated and for that reason the subject can hardly be passed without some further explanation. Its effects are two-fold. In the first place it is always desirable and highly important that wireless messages should be, so far as is possible, selective, inasmuch as there are often several stations in the same immediate neighborhood operating at the same time. This result is reached by tuning and it is possible for them all to transmit different messages at the same time without confusion by the proper arrangement of the wave length. The second effect is the transmission of messages over long distances with the comparative consumption of small amount of power by adjusting the "period" or electrical length of the circuits until the oscillations "flow in harmony" with each other and resonance is secured.

Perhaps the only way that these results may be made clearly intelligible is by resort to a graphical example. Suppose that a very heavy weight were suspended from a chain as shown in the illustration and that it is struck at regular intervals, once every second, with a hammer.

Every time that the hammer strikes the ball it will give it an impulse and cause it to swing slightly. If the chain is short, the ball will swing faster, while if it is long it will swing more slowly. We will suppose that the ball is struck from such a direction that it starts to swing over toward A. The ball is so heavy and the hammer so light in comparison however that the ball does not swing very far and soon commences a return journey. If it should return to the point B just as the hammer delivers another blow the force of the blow will be expended in stopping the ball rather than adding to its motion because they are both traveling in opposite directions. However if the chain is lengthened so that it has a period of swing lasting one second, the succeeding blow will strike the ball after it has reached the point C and is on its return journey, thus imparting fresh energy because both the ball and hammer come together at the right time when they are both swinging together. Proper adjustment of the length of the chain will make it possible for the hammer to always descend at the right moment to add its energy and motion to that previously given the ball. The result will be considerable increase in the amplitude of the swing.

From this we may easily perceive how it is possible by shortening or lengthening the period of an electrical circuit to so adjust it that resonance is secured and each succeeding oscillation will take place at the proper time to assist the previous one, not dying away after one or two surges and becoming what is known in technical language as rapidly "damped."

The instruments for accomplishing these things consist as previously explained, in the case of a transmitter, of the helix and in the receiving station of various tuning coils and condensers.

Helix and tuning coils are divided into the "inductive" or "loose" and the "direct" or close coupled types. Inductive tuning coils are known as "loose-couplers" and "receiving transformers." Inductive helixes consist simply of two helixes, separated from one another as shown in the accompanying illustration. The upper helix, called the secondary, can be raised or lowered upon a central support. Varying the distance between the primary and secondary is varying the "coupling." There are several advantages derived by using loose coupled sending helixes, the chief of which lie in the fact that it is possible to radiate larger amounts of energy and also decrease the "damping."

In order to tune a transmitter, the "hot-wire" ammeter is necessary. This instrument makes use of the property which electrical conductors possess to become heated and expand when a current is passed through them.

The accompanying diagram serves to illustrate the principle of the "hot-wire" meter. A piece of platinum wire is stretched tightly between two rigidly fixed posts. A thread leads from the center of the "hot wire" to a small spindle around which it passes once or twice. The spindle is also connected to a spring which exerts a continual tendency to turn the spindle but is prevented from so doing by the thread attaching to the hot wire. Any tendency on the part of the string to slacken a little, however, will immediately permit the spring to turn the spindle. When a high frequency current is passed through the platinum wire it becomes heated and expands. The expansion of the wire allows the thread to slacken slightly with the immediate result that the spindle turns. The spindle carries a pointer at the upper end which shows the amount of turning. It is therefore easy to tell the comparative strength of current flowing accordingly as the deflection is great or small.

The meter is placed in series with the aerial and when the high frequency currents pass through it they heat and expand a fine wire, causing the needle to move over a graduated scale and indicate the amount of current passing. The apparatus is "tuned" or in resonance when the length of the spark gap, the condenser and the helix have been so adjusted that the oscillations flow freely through the system and the maximum amount of current is indicated by the ammeter.

The loose coupled tuning coil consists of two windings wound over two concentric cylinders, forming a primary and a secondary. The secondary is the smaller winding and slides in and out of the primary so that the "coupling" is variable. The primary is adjustable by means of a slider and the secondary by means of a multi-pointed switch. The slider is usually connected to the aerial and one end of the coil to the ground. The detector, etc., are connected to the terminals of the secondary. Variable condensers may be added with good results to both the primary and secondary circuits.

Loose couplers also take the form of doughnut tuners in which the secondary revolves instead of slides. The coupling is variable in such an instrument by simply turning the secondary.

The wave emitted from a transmitter is in reality made up of two waves of different lengths. The variation in the lengths of these two waves is dependable upon a factor known as the coefficient of coupling. It is almost impossible to clearly explain the phenomenon and in order not to confuse and complicate by a rather lengthy explanation it may be well to simply state that its effect is to make selective tuning difficult unless the coupling of the receiving station can be varied to correspond with that of the transmitter and ask the reader to take it for granted. Varying the coupling adjusts the difference in the two wave lengths and when properly accomplished renders the apparatus highly selective.

Directive Wireless Telegraphy is an interesting phase of this new art which is receiving considerable attention in the hands of investigators and has resulted in the devisement of several successful systems for confining the propagation of the electric waves to certain directions.

A general diffusion of waves is often very undesirable for the reasons that the message may be received by an unfriendly neighbor or enemy and also because it is wasteful of energy. By so directing the waves that they may be sent over the earth to any desired point of the compass and only in that direction, it is possible to communicate without disturbing another station and also for a vessel at sea to secure its bearings and position by tuning its apparatus to respond to electric waves from two different known stations.

The manner in which the problem has been solved varies considerably according to the inventor. All are interesting and ingenious.

It will be remembered that electric waves possess all the characteristics and properties of light waves, etc., and may be reflected, refracted and polarized.

Ferdinand Braun has devised a system consisting of a number of metallic strips arranged to compose a parabolic surface. Another similar set of strips below the first set completes the arrangement. The two sets are connected to the terminals of a spark gap and induction coil. This apparatus acts as a huge reflector and sends out waves in one direction only, but however interesting and ingenious it may be is not entirely practical.

Another method devised by Braun employs two or more aerials at certain distances apart. The alternating currents used to excite the oscillations differ in phase, i. e. are so arranged that they have different comparative values at the same moment. It is possible to send very strong signals in a direction lying in the same plane as the aerials. By the use of three or more antennae suitably differing in their phase of excitation and situated at the vertices of a triangle it is possible to send strong signals in certain directions only.

Messrs. Bellini and Tosi have devised a very ingenious method of directively transmitting and receiving electric waves as shown in the accompanying diagrams. The antenna consists of two closed or nearly closed circuits of triangular shape arranged in two perpendicular planes. The two aerials each contain a circular coil of wire perpendicular to each other with their windings in the planes of the antenna circuits respectively. A third coil is connected to the receiving apparatus when the messages are incoming and to the condenser, spark gap and coil when the signals are to be transmitted.

Waves coming in from any particular direction produce oscillations in the two aerial circuits whose intensity varies according to the direction in which the waves These currents passing through the coils generate a magnetic field having a direction perpendicular to that from which the waves come. The strength of the currents in the movable coil will depend upon its position in the resultant magnetic field and will be at a maximum when the coil embraces as many as possible of the lines of magnetic force.

By providing the movable coil with a pointer it is possible to thereby determine the plane in which the station producing the signals lies. Any ambiguity regarding the final position of the station, whether it is located in the same direction indicated by the pointer or in the opposite one, is only removed by general knowledge of the location of existing stations.

The processes involved in sending messages are the reverse of those entering into the receiving apparatus. The movable coil being connected with the condenser, gap and transformer or induction coil creates a magnetic field which induces oscillating currents in the other two coils and consequent waves in the aerial whose strongest exertions will lie in a plane determined by the third coil. Changing the position of the latter will send the messages in any direction desired.

CHAPTER VI. THE DIGNITY OF WIRELESS. ITS APPLICATIONS AND SERVICE. WIRELESS IN THE ARMY AND NAVY. WIRELESS ON AN AEROPLANE. HOW A MESSAGE IS SENT AND RECEIVED.

Wireless telegraphy and that precocious infant, wireless telephony, have outlived all the speculative and tentative achievements of their early days and have established themselves in an important and settled position among our methods of conveying intelligence.

The field has been so greatly enlarged in recent years and the apparatus and methods so improved that the broadest possible view of its future development and importance is justified. And there must inevitably come the time when our merchant marine and wireless service will come under such reasonable regulation that it will be removed from any dependence upon stock jobbing wireless telegraph and telephone companies.

Official sources show that the equipping of sea-going vessels with wireless apparatus is progressing at a rapid rate and it is not difficult in the face of certain facts to appreciate the enormous volume of business that sooner or later will be handled by wireless. Three hundred and sixty-three United States naval vessels and about eight hundred merchant vessels are equipped at this writing. The large number of commercial shore stations, army forts and posts, and those used by corporations, isolated stations, etc., for various private purposes comprise a list which reaches an enormous total.

Whatever may have been the status of wireless previous to the Titanic disaster, it now occupies a position far more important than that taken merely from any commercial standpoint, for it is no longer merely a convenience to business or a means of furnishing the latest news for the entertainment of passengers, but is a life-saving proposition taking its place with the elaborate and costly systems of railroad signals.

It is a curious fact that many of the most startling and newest inventions find ready and peculiar application as an aid in modern warfare. The nerves of every war vessel and fort are the wires of the telephones, telegraphs, telautographs, dynamos, storage batteries etc., that transmit orders by speech or in writing, find the range, fire the guns, explode the mines and seek out the enemy with a powerful searchlight.

Every battle-ship, cruiser, etc., of the United States Navy is now equipped and with the completion of the new ultrapowerful station at Washington the War Department will be enabled to issue instructions to a ship no matter where it may be on the ocean or in what harbor it may lie.

The government maintains an elaborate equipment at the Brooklyn Navy Yard where the future wireless operators of the Navy are given a course extending from seven to ten weeks. The first few days are spent in mastering the theory. The second week usually commences alternate study and practice of the Continental Code which lasts throughout the entire course or until thoroughly mastered. Each week some special branch of study is given out such as repairing and overhauling certain instruments. At the end of seven weeks the student can usually send and receive 15 words a minute. He is then given two weeks to prepare for an examination which if passed rates him as an electrician, third class, and qualifies him for active work.

This method of transmitting army orders is quite dependable. With the most recent developments and improvements it is now possible to direct the movements of a great army and navy simultaneously from a centrally located point.

One of the most interesting and spectacular applications of wireless telegraphy in military service is the wireless telegraph automobile.

The automobile is a stock pattern touring car of 30 H. P. provided with a special body arranged to carry six passengers. The seats are elevated so as to afford storage space below for the entire wireless equipment and a truly astonishing amount of miscellaneous supplies.

The mast used to elevate the aerial is of light steel construction divided into eight sections which nest into one another with admirable economy of space. The socket for the foot of the mast is located in the center of the tonneau. Only a few minutes are required to raise the mast and aerial. The same gasoline motor employed to drive the automobile also drives a small dynamo which supplies the electric current for the transmitting apparatus.

Two of these cars have been experimentally operated over a number of the old battle-fields of the Civil War.

The tests were made under all sorts of road and weather conditions but no great difficulty was experienced in establishing communication over distances varying from 35 to 50 miles.

There is probably no application of wireless telegraphy, however, quite as picturesque as the combination of wireless and an aeroplane and the idea of a double seated aeroplane carrying an aviator and a wireless operator hovering over a hostile country to keep the commanding officer informed of all conditions and movements of the enemy.

The huge dirigible balloon Akron in which Melville Vanniman proposed to cross the Atlantic Ocean was fitted with wireless equipment in order to transmit news of the expedition en route to various of the daily newspapers of New York and London and also in case of an accident or emergency to summon aid.

The equipment is interesting because of the peculiar conditions imposed upon instruments to be used under such circumstances. A three kilowatt transformer, the latest type of musical rotary gap and a valve detector were included in the outfit. It was proposed to obtain the necessary ground connection by trailing a 1200 foot phosphor bronze ground lead in the ocean. The frame of the balloon was to be used as the aerial. Should it have become necessary to take the lifeboat which the balloon carried, a kite would have been raised and by substituting a copper wire in lieu of a string an aerial provided, and once more a CQ D and its appeal for aid would have gone vibrating forth through the ether.

Several enterprising newspapers have recognized the value of wireless telegraphy in collecting shipping news and have installed outfits for the assistance of their reporting bureau. This innovation in modern journalism has quickly developed into a useful feature of those publications which have seen fit to adopt it. When the baseball season is under way every steamship within calling distance wants the latest baseball scores or sporting results.

Railroads have found an auxiliary wireless service to be of the utmost value in relieving the heavily loaded wire lines between important centers. During some of the winter storms and blizzards, when miles of wires were down in all directions, wireless has been the sole means of communication in certain instances.

The process of sending a wireless message is very simple. The aerial switch is usually kept in such a position that the receiving instruments are connected to the ground and aerial so that the operator is always able to hear any one calling him. We will suppose for illustration that the land station at 42 Broadway, New York City, wishes to transmit a message to the steamer "Horatio Hall."

Every wireless station on land or sea has assigned to it two or more "call letters," which distinguish it from all other stations, and serve as the key to messages intended for it to receive and when signed to a message as an indication of its origin. The "call" of the land station in this case is N. Y., and that of the steamer, J. H.

In order to send the message to the ship, N. Y. throws the aerial into position for sending. This act also starts the motor generator set supplying current to the transformer. Pressing the key, the operator then signals in the telegraph code J. H., J. H., J. H.—M. S. G.–N. Y.—and gives the "finish" signal. M. S. G. is the abbreviation for message. The N. Y. operator then throws his switch back into the receiving position and waits for a reply. If one is not forthcoming shortly the calling process is repeated.

As soon as the operator on board the steamer hears the call, he waits until the finish signal is received, and then responds in the following manner: N. Y., N. Y., N. Y.—J. H.—O. K., O. K.—G. A.—G. A.—N. Y., J. H.—and gives the "finish signal." O. K. is the abbreviation for "all right," and G. A. means "go ahead." Upon receipt of this, the land station transmits the body of the message, and signs its call and finish signal. If the steamer understands the message, she replies "O. K.," and signs.

There are two Codes in general use for wireless telegraph purposes, the Morse and Continental. It takes about five per cent. longer space of time to send a message in Continental than it does in Morse, but the former has the advantage of not containing any letters requiring proper spacing in order to be recognizable. American coastwise steamers use the Morse code; transatlantic ships use the Continental code.

One of the greatest disadvantages of most systems of wireless telegraphy lies in the fact that no arrangement is provided for simultaneously transmitting and receiving wireless signals. It is usually necessary for one operator listening to another to have to wait until the finish signal is given before he can reply or interrupt in case he cannot understand part of the message, because the receiving apparatus of the transmitting station is necessarily disconnected from the aerial and the ground during the period a message is being sent. If it were to be connected at this time the powerful currents of the transmitter would rush through the receiving apparatus into the ground without setting up any very powerful waves in the aerial and seriously injure the delicate receiving instruments.

The Breaking-in-System is a method of simultaneously transmitting and receiving wireless signals. This is accomplished by providing the transmitting key with a second set of contacts, so arranged that when the key is released between the dots and dashes of the code the aerial and ground are automatically connected to the receiving apparatus. When the key is pressed the receptor is automatically cut off. The advantages of such a system are more or less obvious. When interference or a misunderstanding occurs the fact can be immediately signaled to the sending operator, and the message commenced over again.