Detrola Radio Television Corporation v. Hazeltine Corporation
| Decision Date | 12 May 1941 |
| Docket Number | No. 666,666 |
| Citation | 85 L.Ed. 1319,313 U.S. 259,61 S.Ct. 948 |
| Parties | DETROLA RADIO & TELEVISION CORPORATION v. HAZELTINE CORPORATION |
| Court | U.S. Supreme Court |
As Amended on Denial of Rehearing Oct. 13, 1941.
Mr. Samuel E. Darby, Jr., of New York City, for petitioner.
Mr. William H. Davis, of New York City, for respondent.
July 7, 1927, Harold A. Wheeler applied for a patent for a circuit designed automatically to control the amplitude of amplified signal voltage in modulated carriercurrent signalling systems. Patent No. 1,879,863 issued September 27, 1932, to the respondent as assignee of Wheeler.
A suit was brought in the Eastern District of New York for infringement of Claims 1, 5, 6, and 10.1 The District Court held the claims invalid for want of invention. The Circuit Court of Appeals for the Second Circuit affirmed the decree.2
September 26, 1934, while the appeal to the Circuit Court of Appeals was pending, respondent applied for a reissue. After the decision of the Circuit Court of App als respondent redrafted the claims and, October 29, 1935, a reissue patent, no. 19,744, was granted. The present suit was thereafter instituted against the petitioner for infringement of all the thirteen claims of the reissue except Claim 8. The District Court held the patent valid and infringed and its decree was affirmed by the Circuit Court of Appeals.3 The petition for certiorari presented, inter alia, the question whether the decision conflicts with that of the Second Circuit.
Control of the amplification of a modulated carrier-wave signal is useful in connection with transmitting and receiving apparatus and, in the original patent, Wheeler claimed his system as respects both. In his specifications, however, he confined himself to its application to receivers, wherein its function is to control the volume of sound emitted from the loud speaker. In broadcasting, a high frequency wave, known as a carrier wave, is impressed with another low frequency wave or, as it is said, modulated. The high frequency, or signal, wave is picked up by the antenna of a receiver and conducted thence to the input of an amplifying device which consists of an amplifier tube, or several of them in series. These tubes have three electrodes, a cathode, an anode, and a grid, and are called triodes. The signal wave, as amplified, is carried from the output of the amplifying device to the input of a vacuum tube, known as a detector or rectifier, which transmutes the alternating current into a unidirectional or direct pulsating current. This is led to audio tubes which enhance its volume, and thence to a loud speaker. Such a receiving set has other equipment for selecting signals of varying frequency and adjusting the amplification of the audio waves, with which we need not concern ourselves.
One of the problems of the art has arisen from variations of the received signals. When the set is tuned from a weak signal to a much stronger one the tendency is for potential to build up in the last amplifying tube, which results in what is known as blasting in the loud speaker. Often the same signal varies in intensity. Weakening may result in fading, whereby the sound production weakens or disappears; and strengthening may beget distortion of the sounds emitted.
Wheeler essayed to obviate these objectionable features. It was known that the amplification of the carrier signal could be controlled by increasing or decreasing the potential upon the grid of a triode amplifier. Wheeler proposed automatically to vary this potential so as to increase or decrease the degree of amplification and thus hold it at a substantially predetermined level. To this end he provided means to increase the negative potential upon the anode of the detector tube in step with the increased strength of the signal and to conduct a direct current from that anode to the grid electrode of one or more of the amplifying tubes. Thus an increase of the strength of the signal would automatically increase the negative potential on the grid of the amplifier and decrease the amplification; the reverse result would be effected if the signal weakened. The means he adopted to accomplish this were alternative.
According to one method the signal was amplified to a comparatively high voltage, and a diode used as a detector. The output voltage from the detector was approximately as great as that of the amplified signal. By coupling the cathode and anode of the detector and inserting a resistance in the coupling he could maintain the anode of the detector slightly negative at all times. Since he connected all the cathodes in parallel the cathode of the detector was maintained at substantially the same potential as the cathode of the radio frequency am- plifier. By this means the anode of the detector could be maintained normally negative relative to at least a part of the amplifier cathode. When the rectified current flowing t rough the detector circuit increased with the strength of the signal there was developed at the output terminal of the detector circuit, through the operation of the resistance, which was also connected between the anode of the detector and the grid of the amplifier, an increase of negative voltage which, through the direct current connection from the terminal of the detector circuit to the grid of the amplifier, increased the negative potential thereof, and lessened the signal amplification. Conversely, if the strength of the signal current decreased, the negative potential developed upon the anode of the detector correspondingly decreased and there was a decreased inhibition of the amplifying power of the signal amplifier.
In his alternative method, he accomplished the same result with a triode detector. In this arrangement he maintained a negative voltage on the grid of the detector triode by the use of a battery and a potentiometer connected across the cathode of the detector tube. The output circuit of the detector included a resistance connected between the anode of the detector and the common 'B' battery of a radio set. A direct connection was provided from the output terminal of this circuit to the grid of the signal amplifier for impressing thereon the potential developed on the anode of the detector. The amplified signal voltage operated to bring into play the voltage of the battery which created the potential on the anode of the detector.
According to the specifications, each arrangement had advantages and disadvantages. The diode detector used in the first furnished no amplification but it dispensed with the necessity of an additional battery or source of current supply. The second not only required an addi- tional battery but an adjustment between the voltage delivered by the two batteries which cooperate to vary the negative potential on the anode of the triode detector.
Both arrangements include devices to prevent the passage from the detector to the audio tubes, and from the detector to the grid of the amplifier tubes, of undesired forms of electrical energy and both embrace means to provide a time constant with respect to the transmission of negative potential from the anode of the detector to the grid of the amplifier. None of these are now asserted to be novel or to constitute a part of the asserted invention.
In Wheeler's drawings and specifications he exhibited both methods and said of them that they operate 'substantially in the same manner', and again that they are 'substantially similar in operation.' In his application he presented claims which did not specify the kind of detector to be used, and others calling for a diode. All of the latter were disallowed and he concurred in their cancellation without prejudice. he had asserted in prosecuting his application that 'the invention can obviously be used with any kind of detector.' Nine claims were...
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