Armstrong v. De Forest Radio Telephone & Telegraph Co.

• Decision Date: 13 March 1922
• Docket Number: 198.
• Citation: 280 F. 584
• Parties: ARMSTRONG et al. v. DE FOREST RADIO TELEPHONE & TELEGRAPH CO.
• Court: U.S. Court of Appeals — Second Circuit

280 F. 584

ARMSTRONG et al. v. DE FOREST RADIO TELEPHONE & TELEGRAPH CO.

No. 198.

United States Court of Appeals, Second Circuit.

March 13, 1922

Walter H. Pumphrey, of New York City, for appellant.

Pennie Davis, Marvin & Edmonds, of New York City (Thomas Ewing William H. Davis, W. Brown Morton and Willis H. Taylor, Jr. all of New York City, of counsel), for appellees.

Before ROGERS and MANTON, Circuit Judges, and KNOX, District Judge.

MANTON Circuit Judge.

The patent in suit was granted for a wireless receiving system on October 6, 1914, and on an application filed October 29 1913. There are 12 claims in suit. All are held to be infringed by the decree below. The invention relates to improvements in the arrangement and connections of the electrical apparatus and receiving station of a wireless system and particularly a system in which the so-called audion is used as the Hertzian wave detector; the object being to amplify the effect of the received waves upon the current in the telephone or receiving circuit, to increase the loudness and definition of the sounds in the telephone or other receiver, whereby more reliable communication may be established or a greater distance of the transmission becomes possible.

There are several defenses interposed, including the one of noninfringement. The primary question is whether or not the patentee invented the feedback circuit, with an explanation of what it is. The patentee states that he has modified and improved upon the arrangement of the receiving circuits; that the improved arrangement corresponds with the ordinary arrangement of circuits in connection with an audion conductor, in that it consists of two interlinked circuits, a tuned receiving circuit in which the audion grid is included, and which is referred to as a tuned grid circuit, and a circuit including the battery or other sources of direct current and the wing of the audion, which is referred to as the wing circuit. The grid circuit passes through a stopping condenser, then through the secondary of the receiver, in parallel with which is the tuning condenser. Thus the circuit passes to the filament, and from the filament to the grid, through the space inside the audion. The plate circuit, starting from the plate, passes through the battery and the telephone receivers in series. Thus the plate circuit goes to the filament, and from the filament through the space inside the audion bulb to the plate. The path of the battery current is from the positive terminal of the battery, through the plate of the audion, through the intervening space of the audion to the filament, from the filament to the telephone receivers, and then to the negative side of the battery. The grid is positioned in the middle of that path of the current from the plate to the filament and inside the audion. In other words, in the space between the filament and the plate of the audion, the incoming high frequency is impressed upon the grid, which is in the path of the flow of the battery current. The high-frequency current or oscillation is received by the antenna or aerial. An oscillation current flows through this aerial, the primary of the transformer and ground. This primary oscillating current induces a secondary oscillating current in the circuit formed by the secondary of the transformer and the tuning condenser. This oscillating current builds up by resonance a potential difference across the coil and condenser, which is transmitted through the stopping condenser, so that it exists between the grid and the filament of the audion. It is the potential on the grid which varies the steady flow of the battery current through the plate circuit. This is the fundamental operation of the audion. A tuned circuit has the same significance as a resonant circuit. It is a circuit whose inductance and capacity are so adequately related as to give it a natural frequency in accordance with the frequency of an impressed oscillating current. The usual way of a single oscillation is through the medium of an antenna and oscillation transformer, a tuned or resonant grid circuit, and a stopping condenser to the grid and filament.

The Armstrong invention consists in applying the variations in the current, which are of radio frequency, in such manner as to transfer energy back into the grid circuit. This was a wholly novel idea. This result was accomplished by two specific means: First, the provision of coupling between the grid circuit and the plate circuit. The specific form of this coupling consisted of the inclusion of the telephone receivers in the common portion of the grid circuit and the plate circuit. This had the far-reaching consequence of automatically transferring radio-- that is, high-frequency-- energy from the plate circuit to the grid circuit. The second means disclosed by Armstrong for achieving regeneration consisted in making use of the inherent coupling present in the audion bulb itself; this coupling being due to the electrostatic capacity between the plate and the grid. This capacity is inherent, and Armstrong's means made it useful and accomplished the result by the insertion of a radio frequency inductance in the plate circuit. From the sending station, radio signals are sent out in the form of radio frequency waves--waves of a frequency above audibility. These waves are received by the antenna, are impressed upon the grid, and alter the potential on the grid. The grid is interposed in a gap between the filament and plate. The plate current flows across this gap, and the variations in the grid potential cause variations in the plate current, which is a current through the telephone. It has been found that, if radio frequency waves are emitted and received continuously in unbroken trains, they would produce a continued unvarying alteration of the grid potential, and a single continued unvarying alteration of the plate current, so that the only response of the telephone would be a 'click' when reception began and another 'click' when it ceased.

To produce intelligent signals or speech sounds in the telephone, the transmitting waves, either when they are transmitted or after they are received, must be broken up and modulated, to produce interrupted or varying wave trains, and in consequence interrupted or varying alterations of the grid potential. In the use of the detector, wave trains must thus be interrupted or modulated. The effect of the audion as a detector was that the integrated effect of a train of received radio frequency waves caused an alteration of the grid potential which produced a single pulse of current in the plate or telephone circuit. By audio frequency interruption or modulation of the radio frequency waves, either at the transmitting station or at the receiving station, audible sounds are produced in the telephones. By interrupting or modulating the transmitted waves according to a prearranged system, intelligible signals are transmitted. Heretofore the audion, used only as a detector, was thought to be a device in which radio frequency oscillations existed in the grid circuit and audio frequency impulses-- the result of integration of the radio frequency wave trains-- existed in plate or telephone circuit. The idea of radio frequency oscillation in the plate circuit did not exist.

The patentee, while a student of Columbia University, living in Yonkers, was an amateur wireless operator and had a station at his home. There he made observations which led him to suspect that the radio frequency oscillations might be carried over into the plate circuit with some improvements in the detecting action of the audion. He tuned the plate circuit to radio frequency by inserting in the plate circuit such inductance and capacity as to make it responsive to the radio frequency waves. Then he found, not only that the radio frequency waves could be carried over into the plate circuit, but that they could be there amplified by the energy derived from the local battery in the plate circuit without change of frequency or wave form, and that they could be fed into the grid circuit, where they increased the potential variations on the grid and the operation continuously repeated itself, producing the feedback regeneration which increased normally the sensitiveness of the device and the loudness of the receiving signals. It was in this way that he thought out his invention, which has been a great advance in the wireless art. In this feedback audion circuit, as disclosed by the patent, the incoming signal is impressed upon the grid in the same manner with the simple audion circuit, but the flow of current in the plate circuit is varied in a very different manner. Now, because of the feedback connection, regenerative amplification begins. The first half cycle of plate current variation will feed energy to the grid circuit, and will cause a larger subsequent variation in the grid potential. In turn, this increased variation in the grid potential will increase the variation in the plate circuit, and this again feeds back energy to the grid and increases its potential generation in the third and succeeding half cycles. This cyclic process continues to build up the variations in the plate current and grid potential as shown. The building up of the oscillations continues indefinitely, and the limitations are due only to the vacuum tube or audion, which weaken the feedback or regenerative action, as strong oscillations are built up. If the regenerative or feedback coupling is sufficient to transfer enough energy from the plate circuit to the grid circuit, the energy released from the battery in the plate circuit will be greater than the entire loss of energy in the system of circuits, whereupon continuous independent electrical oscillations will...