Reginald Fessenden, who was born in Canada in 1866, had a comprehensive and varied technical background, having worked as a researcher, inventor, and college professor. In 1900, he left his position as chair of the Electrical Engineering department at Western University, in Pittsburgh, Pennsylvania, in order to work with United States Weather Bureau. He quickly became known as one of the most advanced workers in this new field.
Electrical World and Engineer, June 29, 1901, page 1103-1104:
Wireless Telegraphy.
BY REGINALD A. FESSENDEN
EVEN an experimenter working along similar lines and finding a considerable number of devices which he had considered as peculiarly his own, described in the paper, may be pardoned for feeling a considerable degree of pleasure in reading the admirable communication recently made by Mr. Marconi to the Society of Arts. Mr. Marconi is certainly to be congratulated not only upon the practical results which he has achieved, but also upon the beauty of the methods employed. It is most certainly apparent that his method has now passed from the original crude stage to a practical and commercial one.
It may be of interest to compare the results, at least some of them (for it would be inadvisable at present to publish more than a part), obtained on this side of the water by the United States Weather Bureau. These experiments were commenced under the direction of the chief of the Weather Bureau, Professor Moore, in January, 1900. Under his direction and with his approbation the subject was investigated from the beginning, with a view first to finding out definitely the nature of the phenomena, and then devising means for utilizing the forces to best advantage. First will be described a number of cases in which the work of Mr. Marconi and that of the Weather Bureau has gone along parallel lines; secondly, the differences between the methods and results obtained so far as published, and, lastly, an indication of work done by the Weather Bureau which has not been, so far as is known at present, duplicated. Naturally, on account of commercial considerations it will not be possible to go into details so much as might be desired, and for the present this deficiency must be excused.
The first point in which parallel results have been obtained is that concerned with the employment of larger capacities, more especially in the form of cylinders. Mr. Marconi describes the use of concentric cylinders, the inner one connected through a self-inductance to ground, and explains very clearly that in the case of wire conductors the electrical oscillations rapidly die away, and that with greater capacity we have a more persistent vibrator.
The following quotation from one of the patent applications of the Weather Bureau experimenters will show that in this respect the same result has been reached, "The employment of simple wires having small capacity as sending conductors is objectionable for the reason that the radiation is so rapid that there are very few oscillations in each discharge, and hence the inductive rise in voltage at the receiving station cannot attain sufficient value to permit of the use of inductive devices for arresting the potential at such station. By the employment of conductors having large capacity at the sending station, and by properly proportioning the self-inductance and resistance, the radiation from the conductor can be so controlled that there will be a large number of oscillations; for example, 50 or more at each total discharge. In other words, the discharge is so controlled that only a small fraction of the total energy is radiated at each oscillation. By thus extending the period of radiation opportunity is afforded for the inductive voltage at the receiving end to rise to its full value. By increasing the number of oscillations for each total discharge from the sending conductor, and by adjusting the receiving system so that its natural periodicity corresponds, or approximately so, to the period of the electromagnetic waves, the distance of travel of the waves is not solely dependent upon the heights of the sending and receiving conductors as has heretofore been held." And the corresponding claim:
"In a system of wireless telegraphy a conductor adapted to radiate electromagnetic waves having its capacity, inductance and resistance so proportioned that only a relatively small fraction of the energy of the large conductor is radiated during a single oscillation, thereby preventing rapid vibrating in oscillations substantially as set forth."
As regards the details by which this is accomplished, Mr. Marconi uses two concentric cylinders, the inner one having an inductance connected with it. The object of the inductance is not fully described, but Mr. Marconi lays great stress upon it. According to the writer's experiments, the object of this inductance is three-fold. In the first place, as Mr. Marconi explains, it gives a difference in phase; secondly, it is only the outer conductor which radiates, and this radiates just as a simple cylinder of the same size would radiate if used as an ordinary vertical conductor, but for the fact that the oscillations are more persistent when the inductance is put in. For the formula for logarithmetic decrement contains the power, R / L, and hence we can decrease the decrement, i. e., render the oscillation more prolonged by increasing L. Also the two concentric cylinders act as a condenser, and this in combination with the inductance means that we really are shunting the spark-gap with a synchronous circuit of larger capacity, as was suggested by Dr. Pupin in his discussion of wireless telegraphy before the American Institute of Electrical Engineers.
In this respect the work has not been parallel, for while the patent application and the drawings described inductances used in this manner, the same effect has been obtained, not by increasing the denominator, but by decreasing the numerator of the fraction R / L. This has been done in three different ways which will be described at a later date. The advantage of this method is that whilst when we increase the denominator we decrease the period and also decrease the total amount of energy radiated per oscillation, if we decrease the numerator we keep the amount of energy radiated the same and do not change the period, while at the same time we make the logarithmetic decrement just as small as can be obtained with the inductance. This means a greater sending power with a given height.
Another line in which parallel results have been obtained is in the tuning of the secondary of the receiving transformer. Mr. Marconi shows clearly the necessity of this, and we may compare this with the following statement from another of the patent applications:
"It has heretofore been impossible to make the receivers respond solely to waves of one periodicity, as other periodicities, if above a certain power, will affect the receivers. By constructing the second conductor so that the oscillations for each total discharge are increased, and by employing at the receiving station two or more tuned circuits, a very perfect resonance or tuning between the stations can be obtained. With one tuned circuit at the receiving station and with conductors permitting a rapid radiation at the sending station, electrostatic and hysteresis effects become very prominent, and the great self-inductance desirable for sharp resonance cannot be attained. By employing two tuned circuits, one connected to the receiving conductor and the other secondary to the first, the electrical effect in the secondary will occur only when the resonance is very sharp." And the corresponding claim, "In a system of wireless telegraphy a sending conductor in combination with a prime conductor, including the receiving conductor and one or more secondary circuits controlled by the primary circuit; a transmitting device included in the last circuit of the series, the several circuits being tuned to correspond to the period of the second conductor substantially as set forth."
Here, however, there is another difference. Mr. Marconi makes the secondary of his coil equal to the height of the sending conductor. The writer makes it equal to twice the height of the sending conductor. Two explanations of this are possible: First, that Mr. Marconi uses the secondary wound in such a manner that the wire really has a longer natural period than if it were straight; secondly, that he is really working with the first overtone. I have found that the overtones are very pronounced, more especially when the spark length is slightly longer than that generally used. There may be some other cause not at present known, but all the writer's experiments seem to show that the wave length is really four times the length of the vertical conductor and not twice.
Another difference consists in the form of the radiating conductor. Mr. Marconi uses concentric cylinders, but in the Weather Bureau experiments simple cylinders were at first used. Later these were replaced by conductors of the form shown in the accompanying sketch, in which A is a tower, BB are cables insulated from the tower at its top, CC are insulated strain insulators, and DD ropes boiled in an insulating compound. The spark or other apparatus is placed at the top of the tower and the waves go out, as shown by the dotted lines. This kind was later superseded by a third form, and this kind by a fourth, which will be referred to later.
Another case in which parallel work was done is that in which a Thomson high-frequency coil (commonly called a Tesla coil, but in reality first brought out in its present form by Professor Elihu Thomson) was used. Unfortunately, however, some other modifications are used with it, which, as the patents have not been granted, it will be impossible to describe at present. The writer's experiments show plainly that Mr. Marconi's remarks on Professor Slaby's work are justified, and that much better results can be obtained by the Marconi methods.
Lastly, with respect to the general direction in which the work of the Weather Bureau has progressed. In the first place, it has been found possible in several, ways to get over the old difficulty which troubled Hertz, and later experimenters, i. e., that when the spark length was increased beyond a certain length the discharge become no longer oscillatory. An electrical device was invented which, on being applied directly to the sending wire, measured directly the amount of energy radiated. A curve was then plotted, showing the relation between spark length and energy radiated, and it was found that the curve gave a sharp bend with a spark about one inch in length, and no further increase of radiation could be obtained. Different kinds of coils with different primaries and secondaries, different methods of producing the voltage, different kinds of gases and fluid insulators in which the balls were immersed, and different kinds of arrangements of the terminals were tried, but all without success. But finally the solution was found, with the result that with the later apparatus an amount of radiation 16 times as great as that got with the ordinary 12-inch coil and 1-inch spark was obtained. This means, of course, greater sending distance, and it may be mentioned here that transmission without the use of transformers, inductive devices, cylinders or any other apparatus for raising the voltage, has been accomplished over a distance of 50 miles without using more than a fraction of the available energy. The same result was also accomplished in two other ways.
The question of high conductors has proved a rather serious one, because, as Mr. Marconi has pointed out, if we use large surface conductors, though they may be short, yet they are objectionable on account of the wind pressure. Means for overcoming this are described in some of the patent applications, but the method was finally abandoned because means have been found by which a conductor only one meter high can be made to radiate as much energy and of the same period as a conductor 100 meters high. Another difference again has been the fact that it has been found necessary to differentiate in form between the receiving and sending conductors, i. e., to have the receiving conductor with more self-inductance and less capacity than the sending conductor.
Other work done by the Weather Bureau has been along the line of producing a non-interfering system. The admirable and beautiful work of Mr. Marconi has resulted in a system by which within certain limits messages can be sent without interference. But one great objection has been found in the Weather Bureau experiments to this method, although it is described in some of the earlier patents of the Weather Bureau experimenters. That is, that while it is no doubt possible, under certain conditions, to send and receive individual messages, yet by connecting two brass semi-circles to a motor revolving at several thousand revolutions per minute, it is possible to make what may be called an electrical siren which runs up and down a scale of seven or eight octaves several thousand times a minute, and which, as at some period of the scale it gives a note corresponding to any given syntonized receiver, is consequently able to stop all communication, when used in conjunction with the apparatus for strengthening the radiation, within a radius of 500 miles or so. Consequently this method has been superseded by several other methods which permits of selective signaling, no matter how strong the interfering radiator may be or how close it may be, even approaching the interfering radiator within a few feet producing absolutely no effect.
The parallel manner in which a considerable part of this work has been done may possibly be taken as evidence of the fact that the matter has now got down to a sound scientific base. Mr. Marconi and his eminent colaborateur, Dr. Fleming, are certainly to be congratulated on the results they have so far achieved, and no one joins more heartily in wishing them the best of success than the writer. The future of wireless telegraphy in their hands is certainly assured, and it cannot be many years before Mr. Marconi will see the great system which he was the first to see the points of and to put in practical form, in as universal use as our present methods of telegraphy.