Miller v. National Broadcasting Co.

• Court: U.S. District Court — District of Delaware
• Citation: Miller v. National Broadcasting Co., 6 F.Supp. 47 (D. Del. 1934)
• Decision Date: 13 February 1934
• Docket Number: 852.,No. 851,851
• Parties: MILLER v. NATIONAL BROADCASTING CO., Inc. SAME v. RCA COMMUNICATIONS, Inc.

6 F. Supp. 47

MILLER v. NATIONAL BROADCASTING CO., Inc.

SAME v. RCA COMMUNICATIONS, Inc.

Nos. 851, 852.

District Court, D. Delaware.

February 13, 1934.

Hugh M. Morris, of Wilmington, Del., and Clifton V. Edwards and Henry T. Kilburn, both of New York City, for plaintiff.

William G. Mahaffy, of Wilmington, Del., Thomas G. Haight, of Jersey City, N. J., and Abel E. Blackmar, Jr. (of Sheffield & Betts), of New York City, for defendants.

NIELDS, District Judge.

These two suits charge infringement of United States patent No. 1,758,000 for a piezo-electric oscillation generator, granted to John M. Miller April 22, 1930. Broadly, the patent relates to two specific radio signaling circuits and more particularly to circuits utilizing a piezo-electric crystal to control the frequency of oscillations generated with the aid of a vacuum tube with associated circuits including a tuned plate circuit. All claims are in suit except 3, 9, and 10. The alleged infringement consists of the use of crystal controlled oscillators employing tuned plate circuits in certain of the radio transmitting stations of the defendants.

The defenses are (1) invalidity and (2) noninfringement. The defense of invalidity is based upon the state of the prior art, particularly the work of Prof. Cady of Wesleyan University and Prof. Pierce of Harvard College.

"Piezo-Electric" (from to press) is a quality possessed by certain crystalline substances such as quartz. A piezo-electric crystal when compressed develops an electric charge on certain of its surfaces, and conversely, when charged by an electric current, the crystal is compressed and expanded.

Plaintiff specifies as objects of his invention (1) "to facilitate the generation of oscillations of constant frequency"; (2) "to select, at will, any possible mode of oscillation of the piezo-electric substance"; (3) "to permit adjustments to be made for the generation of such oscillations of maximum amplitude"; and (4) "to furnish a convenient means for connecting the oscillator to other tubes for amplification or other uses." The merit and significance of the patent is sufficiently indicated by the first of the above objects.

The claims in issue may be classified in three groups: (1) Those calling for a tuning of the plate circuit; (2) those calling for tuning of the plate circuit at a frequency approximately that of the natural frequency of the crystal; and (3) those calling for a tuning of the plate circuit at a frequency higher than the natural frequency of the crystal where the crystal is connected between the grid and the filament.

A glance at the broadcasting art may throw light upon a proper understanding of the patent. Radio communication is carried on by means of carrier waves transmitted from a radio transmitter through the ether to a receiver. In the transmitter alternating current of 10,000 cycles per second up to several million is fed into an antenna consisting of one or more wires suspended in the air above the ground. This current alternately flowing into and out of the antenna causes waves in the ether which spread in all directions, much as ripples caused by a stone thrown into a still body of water. Successive waves follow one another as long as successive impulses of electric current flow into and out of the antenna. The waves follow exactly both the timing and intensity of alternations of the electric current. The early stations produced these alternations by means of a spark gap. Then followed the use of electric arcs and mechanical generators.

In 1912 De Forest discovered that the vacuum tube could be utilized to generate alternations of electric current at radio frequencies. Thereafter the vacuum tube with its associated electric circuits was used as an oscillator to generate oscillations or high frequency alternating current for antenna, and became known as the "vacuum tube transmitter." Each radio transmitting station is assigned a definite transmitting frequency. To avoid interference, it is essential to maintain that frequency constant. When we turn the dial of a radio receiver, we make it more responsive to waves of one frequency than to those of any other frequency. This is tuning the receiver. It can be made to discriminate between many transmitting stations sending out waves of different frequencies. To enable the receiver to select between transmitting stations, it is essential that the stations transmit at different frequencies or rather at the particular frequency assigned to them. The tube and circuits of the oscillator are so constructed and interrelated that they generate alternating current at the assigned radio frequency. While the vacuum tube transmitter materially improved the stability of frequency as compared with the early forms of transmitting apparatus, the increasing use of wireless and the multiplication of transmitting stations required stability of frequency in order that sending stations would not interfere with each other. This demand for stable oscillations finally led to the adoption of piezo-electric crystals to control the frequency of the oscillations of the vacuum tube transmitter.

Long before the fall of 1923, when plaintiff entered the field, it was a fundamental axiom of radio that "wherever there are high frequency oscillations tune the circuit." For many years before 1923 the use of variable tuning in the plate circuit was fundamental. It had been common practice to employ for tuning a coil and in parallel thereto a variable condenser. In such oscillators the proper plate circuit reactance was obtained by tuning the plate circuit to a frequency either higher or lower than the operating frequency. Long before 1923, tuning by varying the inductance of a circuit was used as the equivalent of tuning by means of varying the capacity of a circuit. It was well known that no result is secured by one method which cannot also be secured by the other method. Before the present litigation, the plaintiff in another case testified that a coil in the plate circuit of a vacuum tube oscillator corresponds exactly to a coil having a condenser in parallel thereto.

Before 1923 the operation of vacuum tube oscillators controlled by electrically tuned circuits was thoroughly understood. It was understood that, where the grid-plate circuit is capacitative, the plate circuit must be tuned to a higher frequency than the operating frequency; i. e., have an inductive reactance at that frequency. Where the grid-filament circuit is capacitative, the plate circuit must be tuned to a lower frequency than the operating frequency; i. e., have a capacitative reactance at that frequency.

The method of operation of circuit controlled oscillators has been indicated above in general terms and is particularly disclosed in the work of Armstrong and Heising. The method and theory of operation of crystal controlled oscillators and of circuit controlled oscillators are the same. There is no fundamental difference between the crystal controlled oscillator in Fig. 1 of the patent in suit and tuned circuit controlled oscillators in the prior art including Fig. 3 of the Armstrong patent. The difference in detail is the substitution of the sharply mechanically tuned crystal for the less sharply tuned electrical circuits. Hogan, a recognized authority, testified: "Fig. 1 of the patent in suit and Fig. 3 of the Armstrong patent are both regenerative circuits, having the oscillation frequency controlled by a tuned element. The tuned element in Fig. 1 is the crystal shown at M in the patent in suit. The tuned element in the Armstrong Fig. 3 is the tuned circuit similarly connected between grid and filament and having its frequency determined by its effective electrical capacity and inductance. Fundamentally the two circuits are the same except for the substitution of a crystal having a definite natural frequency for an electric circuit having a definite natural frequency."

Walter G. Cady, professor of physics at Wesleyan University, began experiments with piezo-electric crystals as early as 1917, and is recognized as the pioneer in their use in this country. He was working with them actively in 1920 and 1921. In April, 1922, he published a paper in the proceedings of the Institute of Radio Engineers entitled "The Piezo-Electric Resonator." In his paper he disclosed to the art that a crystal was suitable to control the frequency of a vacuum tube oscillator; that a crystal was a sharply tuned element; that a crystal, like an electrically tuned circuit, had both capacitative and inductive reactance. He treated the crystal as though it were an electric circuit having resistance, capacity, and inductance.

Crystal oscillators employing a tunable plate circuit were used by Cady and his assistant, Van Dyke. The use of a tunable plate circuit to increase the power tube of such oscillators was described by Cady in the Physical Review for April, 1922, in an article entitled "A Piezo-Electric Method for Generating Electric Oscillations of Constant Frequency." In Figs. 2 and 3 of his patent No. 1,472,583, granted October 30, 1923, applied for May 28, 1921, Cady described two crystal controlled oscillators in which the crystal was connected between grid and filament and was an essential element in the generation of oscillations. In both Cady circuits the frequency of oscillation was controlled by a natural frequency of the crystal. In Fig. 3 the plate circuit is tunable indirectly, and in operation is tuned to a higher frequency than the natural frequency of the crystal.

Prof. George W. Pierce, Rumford professor of physics and director of the Cruft Laboratory for high-tension electrical research at Harvard College, became interested in the use of crystals through the work of Prof. Cady. In calibrating wavemeters in the spring of 1923, Prof. Pierce fabricated and utilized a crystal controlled oscillator in which the crystal was connected between grid and plate and the plate circuit...