A more technical review of the DeForest radiotelephone equipment--arc transmitters and audion receivers--used on the "Great White Fleet" voyage.
Telephony, May, 1908, pages 365-367:
WIRELESS TELEPHONY FOR THE NAVY
A Description from the Scientific American of the Radio Apparatus
By Herbert T. Wade
A MOST essential condition of modern warfare is to maintain unbroken and complete communication along the entire line, from the commander-in-chief and the board of strategy to "the man behind the gun." Every device in the way of a signal or telegraph that accomplishes this purpose must be employed, and new inventions are warmly welcomed, especially in the naval service, where to secure the best results a fleet must move at the direction of one man, and often as a single unit. Accordingly, when it was announced recently that wireless telephony had been developed to a practical state, it was but natural that the United States navy should wish early to test its claims, with a view to its extensive adoption for intership communication, as well as for talking between sea and shore or between temporary or isolated stations, as on islands. For such tests apparatus has recently been installed on the United States battleships Connecticut and Virginia by the Radio Telephone Company under the direction of Dr. Lee De Forest, who for several years has been devoting himself to the transmission of articulate sounds by electrical waves, and has developed his apparatus so that the practicability of wireless telephony on a commercial, scale seems assured. If the report of the naval officers supervising these tests is satisfactory, it is quite probable that the new Pacific fleet, at least, will be completely equipped with apparatus for wireless telephony.
The present application and tests involve the installation of transmitting and receiving apparatus in the wheel house or on the bridge of the battle ships, working in connection with, yet quite independent of the ship's ordinary wireless telegraph equipment. This enables the admiral or captain to converse with any ship within five miles, the contract limits of the present installation. The apparatus as now constructed is the result of an exhaustive series of laboratory experiments by Dr. De Forest, combined with practical tests made last July on Lake Erie, where wireless telephony was used in reporting a yacht race to communicate between a small yacht in motion and the shore. On this occasion it was shown publicly that for distances up to four miles, satisfactory telephonic communication without wires is perfectly feasible, and it is with an improved form of this apparatus that tests are being made by the navy. Just previous to shipment to Provincetown for installation on the battleships, and while undergoing the final laboratory testing, the instruments were specially photographed for the Scientific American, and are shown in the accompanying illustrations.
In explaining the construction and operation of the De Forest system, it may be desirable to say a few words as to the underlying theory. Wireless telephony, as also wireless telegraphy, depends upon the production of electric waves that pass through the atmosphere, and also solid substances, with a velocity equaling that of light-186,000 miles per second.
In order to transmit either telegraphic signals or vibrations corresponding to those of the voice, it is necessary to interrupt or vary these waves at intervals depending on the signals or character of the sound. The production and transmission of the waves is essentially the same in wireless telephony as in wireless telegraphy, but their interruption is an entirely different matter. The vibrations corresponding to the human voice have an average rate of about 500 per second, for a man's voice, extending up to 20,000 per second for the overtones, while in wireless telegraphy, manually operated, it is possible to work at a rate of about five interruptions per second, the telegraph signals of course corresponding to the familiar Morse alphabet. In wireless telegraphy the receiving of the waves is accomplished by any one of a number of devices, such as the coherer, the magnetic detector, electrolytic responder, etc., but in wireless telephony there is need of a specially sensitive device, and this is realized in the audion, which, devised by Dr. De Forest and adapted for both space telegraphy and telephony, has been found a specially valuable element in the latter. This instrument, shown in the illustration, appears at first glance to be simply a small incandescent lamp, but there will be noticed a plate and a grid of platinum sealed into the bulb and connected with the exterior by platinum wires. The filament is of tantalum or other metal and is made to glow by a current from a small storage battery. The action will be explained below more fully in connection with the rest of the apparatus whose connections and arrangement are indicated on the accompanying diagrams. At the transmitting instrument current is supplied at 220 volts from the ship's lighting mains or other supply such as a small dynamo driven by an oil engine or a dynamotor using current at a different voltage. This direct current flows through choke coils which prevent the high-frequency alternating current from passing, and then goes to the oscillator, which consists of an arc maintained in the flame of a small alcohol lamp. The production of highfrequency alternations from an arc was first discovered by Duddell in England and has been investigated by several physicists and experimenters, so that it was comparatively easy for Dr. De Forest to adapt the principle to his transmitting apparatus, although the actual application and the construction of a practical device required most elaborate and careful experiment. These currents with a frequency of about 40,000 per second pass through the primary of the transformer as indicated, a condenser being interposed in the circuit. The secondary of the transformer is connected with the antenna or aerial wire of the usual type used in wireless telegraphy, and to the ground through the microphone of an ordinary telephone transmitter. By adjusting properly the two circuits it is possible to produce in the aerial wire oscillations that will cause waves of the desired frequency to be sent out into the air. Now the vibrations of the voice acting on the microphone cause the resistance of the carbon granules to vary, consequently the resistance of the aerial wire circuit varies, and this correspondingly affects the amplitude or intensity of the waves emitted from the antenna, not cutting them off absolutely as in wireless telegraphy. Examining now the diagram for the receiving instrument, a similar aerial wire will be seen connected to the earth through one coil of a transformer, while the circuit of the secondary includes two condensers, the audion with its storage battery, and the telephone with its cells. The electric waves impinging on the aerial wire set up a series of oscillations, which in turn are reproduced in the corresponding circuit of the transformer and affect the audion, causing the resistance of the gas ionized by the heat of the glowing filament to vary in proportion to the amplitude of the oscillations in the aerial wire, and the diaphragm of an ordinary telephone receiver is made to vibrate in the usual manner, reproducing the sound spoken into the transmitter.
The conditions outlined above and explained by the diagrams are realized in the instruments themselves, shown in the illustrations. Here everything is brought together and the adjustments reduced to a minimum, so that by observing a few simple rules there is no need for a trained operator. The illustration shows the complete apparatus for a single station, with the appropriate connections and all adjuncts except the batteries and aerial wires. It will be noticed that the apparatus is simple and compact, occupying little more space than the familiar wall set of the ordinary telephone. The transmitting instrument on the left will be recognized from the familiar microphone transmitter while the instrument is shown again by itself somewhat enlarged. The conductor leading to the aerial wire passes out at the top of the case and the source of current is connected with binding posts at the rear. At the side of the box is the oscillator or arc inclosed in its nickeled casing with the alcohol lamp beneath. This lamp is lighted and the transformer coils contained in the case are adjusted so that oscillations of the proper frequency are produced and waves of the desired length are emitted from the aerial wire. The action of the arc is indicated by the small incandescent "pilot" lamp shown at the top of the box, which is acted on inductively by the current in the primary of the transformer and glows when the oscillation takes place. The tuning of the transmitting circuit is accomplished with the small handle moving in the slot at the side of the box, while a listening key is provided to enable the operator to connect at will the aerial to either transmitting or receiving instrument. There is also a telegraph key and a device resembling the ordinary buzzer which is termed a "chopper" by Dr. De Forest, shown in the foreground of the illustration, which by simply cutting out the microphone with a switch in front of its case, enables the apparatus to be used for wireless telegraphy, sending the ordinary Morse signals. In telephoning, the method is to send a few such signals to attract attention and then to switch onto the microphone or talking circuit. The receiving instrument is contained in the two boxes shown at the right of the illustration. On the upper box is the two "pan-cake" syntonizer or tuning device consisting of two coils where the number of turns can be varied at will, and beneath an adjustable condenser and impedance coils, the whole being tuned of course to the sending apparatus.
The lower box, from which leads pass to the telephone receiver, contains the audion, already described and illustrated, which is provided in duplicate in case of possible mishap, together with suitable switches and resistances to enable the current from the storage battery for the lamp circuit and that from the dry cells, for the telephone circuit to be regulated and used most effectively. The speaker has merely to put the telephone to his ear, using the listening key, and to talk into the transmitter. The simplicity of the apparatus commends it for naval use, as it enables communication to be maintained not only between the vessels of a fleet but with torpedo boats or dispatch boats on detached service in maneuvers or in action. Furthermore, there is a field for use in communicating with colliers and supply boats, not to mention lightships, lighthouses and shore stations generally. With the improvement and increase in the range of action which is bound to follow now that a practical success has been assured, the usefulness of wireless telephony at sea will be widely extended. As a fog signal and means of communication in thick weather, it promises to increase the safety of ocean travel. Wireless telephony has also important applications on land which are attracting the attention of the inventor, but the apparatus above described is of special interest as being the first to be installed on United States naval vessels.