Hazeltine Corporation v. Crosley Corporation, 9096.

• Decision Date: 28 August 1942
• Docket Number: No. 9096.,9096.
• Citation: 130 F.2d 344
• Parties: HAZELTINE CORPORATION v. CROSLEY CORPORATION.
• Court: U.S. Court of Appeals — Sixth Circuit

130 F.2d 344 (1942)

HAZELTINE CORPORATION v. CROSLEY CORPORATION.

No. 9096.

Circuit Court of Appeals, Sixth Circuit.

August 28, 1942.

Laurence B. Dodds and Henry T. Kilburn, both of New York City (Paxton & Seasongood and Robert P. Goldman, all of Cincinnati, Ohio, on the brief), for appellant.

Samuel E. Darby, Jr., of New York City (Allen & Allen, of Cincinnati, Ohio, Floyd H. Crews, of New York City, and Alden D. Redfield, of Cincinnati, Ohio, on the brief), for appellee.

Before ALLEN, MARTIN, and McALLISTER, Circuit Judges.

MARTIN, Circuit Judge.

The bill of complaint charging infringement of MacDonald Patents, Nos. 1,913,604 and 2,022,514, owned by appellant, was dismissed in the district court on the ground that the patents were not infringed. Decision on the issue of the validity of the patent claims was pretermitted.

The patents, relating to vacuum tube radio receivers, describe a wave signaling system; and the invention, as defined by appellant, provides an antenna primary inductance suitable for connection to a capacity antenna, in which the inductance is of such value as to insure resonance of the antenna primary circuit at a frequency below or of the order of the lowest frequency of the tuning band for all usual values or sizes of antennas, the primary inductance being magnetically coupled to the tunable secondary circuit. Appellant relies upon claims 1, 6 and 8 of Patent No. 1,913,604, and upon claims 5, 22, 24 and 25 of Patent No. 2,022,514, the former patent being a division of the latter.

The claim selected by appellant as typical is No. 1 of the divided patent, No. 1,913,604, which reads: "In combination, a capacitive antenna system containing no lumped inductance, and a radio-frequency system for coupling thereto comprising, a circuit tunable by a condenser throughout a frequency range, a transformer having a secondary coil included in said tunable circuit, and a primary coil electromagnetically coupled to said secondary, said primary coil being adapted for connection to said antenna system and having an inductance insuring resonance of the antenna system at a frequency fixed below said range." Claims 6 and 8 of the same patent, which are substantially similar to Claim 1, are quoted below.¹

In support of the charge of infringement, appellant relied upon Crosley Radio Receiver Model 519, manufactured and distributed by appellee.

The findings of fact filed by the district court state:

"4. The two patents in suit were allowed by the Patent Office to cover and to be restricted to an antenna primary winding or coil, in a radio receiver, which primary winding itself, without any other connected instrumentalities, is resonant at a frequency below the broadcast band.

"5. The antenna primary coil used by defendant in the accused set is resonant at 850 kilocycles well within the broadcast band which extends from 550 kilocycles to 1500 kilocycles.

"6. It was conceded at the trial by counsel for plaintiff that the accused set does not include an antenna primary winding which itself, without any other connected instrumentalities, is resonant at a frequency below the broadcast band.

"7. It was likewise conceded at the trial by counsel for plaintiff that the patents in suit do not disclose an antenna transformer having a primary winding which itself, without any other connected instrumentalities, is resonant at a frequency below the broadcast band."

At the outset of discussion, a few generalizations may be clarifying. All radio communication is made possible by the transfer of energy in the form of electromagnetic waves. Electromagnetic waves are disturbances in the ether, deliberately created at a radio transmitting station and propagated in all directions through space. The length of an electromagnetic wave is the distance which the wave travels in one cycle. The frequency of the wave is the number of cycles per second.

The first problem of radio reception is to capture the energy in these electromagnetic waves. The fundamental tool employed by the radio designer to that end is a resonant circuit comprising inductance and capacity.

Inductance is that property in an electrical circuit which tends to resist or impede any change in the flow of the electric current. This resistance will increase as the frequency of the current increases. The property of inductance is associated with a wire, usually in the form of a coil. The inductance of a coil depends upon the number of turns, the manner in which the wire is wound, and the material on which it is wound. Capacity serves to store electricity. It is a property associated with two or more spaced electrical conductors, causing the impedance or resistance of the electrical circuit to decrease as the frequency of the current increases. In its effect, capacity is directly opposite to inductance.

When inductance and capacity are associated, a circuit is formed which may be excited by electromagnetic waves. When the frequency of these waves is such that the properties of inductance and capacity in the circuit effectively cancel each other, the circuit becomes resonant. A resonant circuit, excited by a radio signal of the same frequency as the resonant frequency, can amplify the radio signal to a strong oscillatory voltage capable of further amplification in succeeding parts of the receiver.

The natural period of resonance or vibration of each circuit depends upon the amount of its inductance and capacity. By adjusting the value of either inductance or capacity so that the natural period of oscillation of a circuit is the same as that of the oscillating current to be received, any circuit containing inductance and capacity may receive currents of one particular frequency and reject those of all other frequencies. A circuit containing both inductance and capacity variable in value is termed a "tuned circuit"; and receivers employing tuned radio frequency circuits with amplifying vacuum tubes electrically connected in series became known as "Tuned Radio Frequency," or "TRF" receivers.

The TRF receiver possessed essentially one or more amplifiers of high frequency currents, a vacuum tube detector and one or more vacuum tube amplifiers of low frequency currents. The vacuum tubes were glass bulbs which contained three separated electrodes, consisting of a filament and a plate, with a grid shaped metallic member placed in the space between them. The grid electrode constituted one terminal of the tuned input circuit of the tube, and the plate electrode constituted one terminal of the output circuit. The filament electrode was common to both input and output circuits of the tube. But TRF receivers were found deficient for the reason that the vacuous space within the tube between the grid and plate electrodes constituted a "coupling" between the input and the output circuit, causing oscillating current to be fed back from the output of the tube through the coupling into the input circuit, with resultant discordant noises. This tendency of radio frequency amplifiers to "break into oscillations" was cured by an invention of Professor Hazeltine. Hazeltine's invention, which became known as a "neutrodyne radio receiver," neutralized the coupling between the plate and grid electrodes within the tube by means of a circuit external to it.

The validity of the Hazeltine Neutrodyne patents was established by litigation, and practically all manufacturers of marketable receivers paid tribute thereto by becoming licensees under the appellant Hazeltine Corporation, which was created to acquire and hold ownership of the Hazeltine patents. The appellee corporation, which was among the first manufacturers and distributors of radio and broadcast receivers, became a licensee of appellant and remained such until June 30, 1939.

After widespread usage, the Hazeltine Neutrodyne receiver was ultimately rendered obsolete by the development of the "screened grid vacuum tube amplifier," which eliminated the coupling effect within the tube.

In order to comprehend the problem which confronted the inventor, MacDonald, it will be necessary to consider the function of antennas, which are merely devices for radiating the energy of electromagnetic currents into space from a sending station, and for intercepting such energy at the receiving station. Having intercepted high frequency radio waves transmitted through the air, the further function of an antenna at the receiving station is to apply the waves to the input circuit of the radio receiver where they can be selected and amplified. The patents in suit are directed to the circuit associated with the antenna for applying the intercepted radio signals to the radio receiver proper.

Coupling transformers comprised of primary coils of a very few turns and quite low inductance had been customarily used prior to MacDonald's invention. As a result, the antenna circuit was resonant with the usual antenna at a frequency above the tuning range of the receiver. This condition naturally reflected capacity into the first tuning circuit, causing a detuning effect, since the first circuit would be tuned to a different frequency from that of the other circuits. If the inductance of the antenna circuit was increased to an extent that the circuit became resonant within the tuning range of the receiver, the detuning effect was increased. The other tunable circuits being essentially capacitive, the receiver tended to offer less resistance or impedance at high frequencies, making the problem of amplification at the low end of the tuning range more acute. The radio designer thus faced the horns of a dilemma. If he attempted a maximum of amplification, he must couple the antenna circuit closely with the first, tunable circuit, increasing the detuning effect at high frequencies. If, on the other hand, he coupled the antenna circuit loosely in an attempt to reduce the detuning effect in the first circuit, amplification would be seriously reduced at low...