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a coherer was directly connected. Marconi claimed the construction of transmitter and receiver so as to be resonant to the same frequency, and described means of doing so by careful determination of the size of the aerial plates.
The Tesla patent No. 645,576, applied for September 2, 1897 and allowed March 20, 1900, disclosed a fourcircuit system, having two circuits each at transmitter and receiver, and recommended that all four circuits be tuned to the same frequency. Tesla's apparatus was devised primarily for the transmission of energy to any form of energy-consuming device by using the rarified atmosphere at high elevations as a conductor when subjected to the electrical pressure of a very high voltage. But he also recognized that his apparatus could, without change, be used for wireless communication, which is dependent upon the transmission of electrical energy. His specifications declare: "The apparatus which I have shown will obviously have many other valuable uses—as, for instance, when it is desired to transmit intelligible messages to great distances ..." 11
Tesla's specifications disclosed an arrangement of four circuits, an open antenna circuit coupled, through a transformer, to a closed charging circuit at the transmitter, and an open antenna circuit at the receiver similarly coupled to a closed detector circuit. His patent also in
11 Tesla's specifications state that the current should preferably be "of very considerable frequency.” In describing apparatus used experimentally by him, the specifications state that the oscillations are generated in the charging circuit by the periodic discharge of a condenser by means of “a mechanically operated break," a means whose effects are similar to those of the spark gap generally used at this period in the radio art. He further states that the inductance of the charging circuit is so calculated that the “primary circuit vibrates generally according to adjustment, from two hundred and thirty thousand to two hundred and fifty thousand times per second.” The Opinion of the Court.
structed those skilled in the art that the open and closed circuits in the transmitting system and in the receiving system should be in electrical resonance with each other. His specifications state that the "primary and secondary circuits in the transmitting apparatus” are "carefully synchronized.” They describe the method of achieving this by adjusting the length of wire in the secondary winding of the oscillation transformer in the transmitter, and similarly in the receiver, so that "the points of highest potential are made to coincide with the elevated terminals” of the antenna, i. e., so that the antenna circuit will be resonant to the frequency developed in the charging circuit of the transmitter. The specifications further state that "the results were particularly satisfactory when the primary coil or system A' with its secondary C [of the receiver] was carefully adjusted, so as to vibrate in synchronism with the transmitting coil or system AC.”
Tesla thus anticipated the following features of the Marconi patent: A charging circuit in the transmitter for causing oscillations of the desired frequency, coupled, through a transformer, with the open antenna circuit, and the synchronization of the two circuits by the proper disposition of the inductance in either the closed or the antenna circuit or both. By this and the added disclosure of the two-circuit arrangement in the receiver with similar adjustment, he anticipated the four-circuit tuned
range of radio frequencies in use in 1917 was said by a witness for the plaintiff to extend from 30,000 to 1,500,000 cycles per second. The range of frequencies allocated for radio use by the International Telecommunication Convention, proclaimed June 27, 1934, 49 Stat. 2391, 2459, is from 10 to 60,000 kilocycles (10,000 to 60,000,000 cycles) per second, and the spectrum of waves over which the Federal Communications Commission currently exercises jurisdiction extends from 10 to 500,000 kilocycles. Code of Federal Regulations, Title 47, Ch. I, $2.71. Thus Tesla's apparatus was intended to operate at radio frequencies.
combination of Marconi. A feature of the Marconi com
ductance as a means of adjusting the tuning of the antenna circuit of transmitter and receiver. This was developed by Lodge after Tesla's patent but before the Marconi patent in suit.
In patent No. 609,154, applied for February 1, 1898 and allowed August 16, 1898, before Marconi's application, Lodge disclosed an adjustable induction coil in the open or antenna circuit in a wireless transmitter or receiver or both to enable transmitter and receiver to be tuned together. His patent provided for the use, in the open circuits of a transmitter and a receiver of Hertzian waves, of a selfinduction coil between a pair of capacity areas which he stated might be antenna and earth. His specifications state that a coil located as described could be made adjustable at will so as to vary the value of its self-inductance; that the adjustment, to secure the "desired frequency of vibration or syntony with a particular distant station," may be attained either "by replacing one coil by another" or by the use of a coil constructed with a movable switch so related to the coil as to short circuit, when closed, any desired number of turns of the wire, "so that the whole or any smaller portion of the inductance available may be used in accordance with the correspondingly-attuned receiver at the particular station to which it is desired to signal.” Thus Lodge adjusted his tuning by varying the
the adjustment of wave lengths, and hence of frequency in the circuits, could be made by varying either or both the inductance and capacity, which are the factors controlling
Lodge thus broadly claimed the tuning, by means of a variable inductance, of the antenna circuits in a system of radio communication. His specifications disclose what is substantially a two-circuit system, with one high fre
Opinion of the Court.
quency circuit at the transmitter and one at the receiver. He also showed a two-circuit receiver with a tuned antenna circuit, his detector circuit at the receiver being connected with the terminals of a secondary coil wound around the variable inductance coil in the antenna circuit and thus inductively coupled through a transformer with the antenna circuit.12 Lodge thus supplied the means of varying inductance and hence tuning which was lacking in the Tesla patent. He also showed a receiver which completely anticipated those of the Marconi receiver claims which prescribe adjustable means of tuning only in the antenna circuit (Claims 2, 13 and 18) and partially anticipated the other receiver claims.
The Stone patent No. 714,756, applied for February 8, 1900, nine months before Marconi's application, and allowed December 2, 1902, a year and a half before the grant of Marconi's patent, showed a four-circuit wireless telegraph apparatus substantially like that later specified and patented by Marconi. It described adjustable tuning, by means of a variable inductance, of the closed circuits of both transmitter and receiver. It also recommended that the two antenna circuits be so constructed as to be resonant to the same frequencies as the closed circuits. This recommendation was added by amendment to the specifications made after Marconi had filed his application, and the principal question is whether the amendments were in point of substance a departure from Stone's invention as disclosed by his application.
Stone's application shows an intimate understanding of the mathematical and physical principles underlying radio communication and electrical circuits in general.
12 Marconi's patent No. 627,650, of June 27, 1899, similarly showed a two-circuit receiving system, in which the coherer was placed in a closed circuit which was inductively coupled with a tuned antenna circuit. The Court of Claims found, however, that this patent did not clearly disclose the desirability of tuning both circuits.
It contains a critical analysis of the state of the art of radio transmission and reception. He said that as yet it had not been found possible so to tune stations using a vertical antenna as to make possible selective reception by a particular station to the exclusion of others. His effort, accordingly, was to transmit a "simple harmonic wave” of well defined periodicity to a receiver which would be selectively responsive to the particular frequency transmitted, and thereby to achieve greater precision of tuning and a higher degree of selectivity.
Stone discusses in some detail the difference between "natural" and "forced" oscillations. He says "If the electrical equilibrium of a conductor be abruptly disturbed and the conductor thereafter be left to itself, electric currents will flow in the conductor, which tend to ultimately restore the condition of electrical equilibrium." He points out that a closed circuit containing a condenser and a coil is "capable of oscillatory restoration of equilibrium upon the sudden discharge of the condenser" and that “the electrical oscillations which it supports when its equilibrium is abruptly disturbed and it is then left to itself are known as the natural vibrations or oscillations of the system.”
In addition to its ability to originate "natural vibrations" when its electrical equilibrium is disturbed, Stone says that an electrical circuit is also "capable of supporting what are termed forced vibrations” when electrical oscillations elsewhere created are impressed upon it. In contrast to the "natural" vibrations of a circuit, whose frequency depends upon “the relation between the electromagnetic constants (capacity and self-inductance] of the circuit,” the frequency of the "forced” vibrations is "independent of the constants of the circuit” on which they are impressed and “depends only upon the period (frequency] of the impressed force.” In other words, Stone found that it was possible not only to originate high