US2206072A

US2206072A - Arrangement for mixing two frequencies in a superheterodyne receiver

Info

Publication number: US2206072A
Application number: US112459A
Authority: US
Inventors: Barthelemy Rene
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1936-01-27
Filing date: 1936-11-24
Publication date: 1940-07-02
Anticipated expiration: 1957-07-02

Description

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I July 2, 1940. R. BARTHELEMY ARRAHGEIENT FOR HIKING TWO FREQUENCIES IN A SUPERHETERODYNE RECEIVER Filed Nov. 24, 1936 UJT/LLATOR ATTORNEY Patented July 2, 1940 UNITED STATES PATENT OFFICE ARRANGEMENT FOR MIXING TWO FRE- QUENCIES IN A SUPERHETERODYNE RE- CEIVER Application November 24, 1936, Serial No. 112,459 In Germany January 27, 1936 4 Claims.

The present invention relates broadly to modulation circuits and more particularly to frequency combining circuits.

Superheterodyne receivers require mixing arrangements permitting two frequencies to be so superimposed that a desired third frequency is thereby produced. A great number of special circuits serving for this end are already known, the modern methods operating exclusively with electron tubes.

The present invention relates to a novel method in which a photo-electric cell plays the part of a frequency combining or mixer tube.

In a photo-cell to which a potential is applied, it is known that current can pass through it only when quantities of light impinging on the cathode, release electrons whereby the emission of thecathode is made possible. Therefore, the photo-current produced can be controlled by the intensity of the impinging light.

In accordance with the present invention, a photo-cell is inserted into the high-frequency receiver circuit tuned to the frequency 11. When the photo-cathode is" exposed to the radiations of a light ray of constant intensity the photo-cell acts as a detector and the high-frequency, as is known wlll be detected in the cell, and thus represents an intermittent current of constant value. But if the intensity of the light source-for instance as when the light source is fed by a second high-frequency fz-is likewise subject to periodic variations, the frequencies 11 and I: will be superposed on each other. The desired intermediate frequency can then be filtered out from the resultant photo-current by means of any suitable resonance circuit.

An application of the invention is shown in the single figure of the drawing-which illustrates schematically a portion of a receiver utilizing the features of the present invention. The arriving high-frequency is herein supplied from an antenna I to a tuning circuit 3, 4. The high-frequency potential appearing in said circuit is applied'to a photo-cell P illuminated by a light source M which may be a glow tube. Light source M is energized by energy generated by a local oscillator 5. Hence, the light intensity of the source M varies in accordance with the frequency of the oscillations generated by the oscillator 5".SiDC8 the incoming signal oscillations and the local oscillations are both effectively impressed upon the photo-electric cell P, it follows that one of the products of the output of the photo-electric cell will be intermediate frequency energyresulting from the combination of the signal oscillations and the local oscillations. The desired intermediate frequency energy may be selected out of the photo-electric cell output by the coupled tuned circuits 6, 1 and 8, 9 and fed to any suitable intermediate frequency utilizing device which may be connected across terminals 10 and II. To receive signals from a station operating on another wave length, the input circuit 3, 4 is tuned to the new wave length and the frequency of the oscillations generated by oscillator 5 is changed so that the same intermediate frequency will be available across terminals i and l l as is common practice with superheterodyne receivers. The oscillation generator has not been shown in detail since any of the well known types of oscillation generating arrangements may be utilized for this purpose.

If however, a relaxation oscillation generator is to be employed, the glow tube thereby used may serve as the light source for illuminating the photo-cell.

One type of relaxation oscillation generator which may be used is shown in U. S. Patent 1,927,425. Another type is shown in U. S. patent application Serial No. 748,773 filed October 10, 1934, by J. P. Smith.

Besides the example referred to, the invention can be utilized in numerous modulation circuits of other types. As compared with the known modulation methods. the greatest advantage of the present invention will lie in the complete de-coupling of the oscillator thereby excluding a reaction upon the preliminary circuits.

What I claim is:

1. In a superheterodyne receiver, a frequency changer circuit for producing intermediate frequency energy from received radio frequency signal modulated carrier energy comprising. in combination, a photo-electric cell having an electron emitting element, means including a source of light energy for energizing said electron emitting element, and means comprising a local oscillation generator device for periodically varying the intensity of said light energy at a frequency which when combined with energy of the frequency of said received radio frequency modulated carrier energy produces the desired intermediate frequency.

2. In a superheterodyne receiver, a frequency changer circuit for producing desired intermediate frequency energy by combining received radio frequency signal modulated carrier energy with locally produced energy of a predetermined frequency comprising, in combination, a photoelectric cell having a light controlled electron emitting element, a light source for applying light energy to said electron emitting element, an input circuit and an output circuit for said photo-electric cell, means for applying the received signal modulated carrier energy to said input circuit, an intermediate frequency resonant circuit included in said output circuit, energizing means for said light source comprising an oscillation generator for periodically varying the intensity of the light energy at a frequency which when combined with the radio frequency signal modulated energy produces energy of intermediate frequency, and a utilizing circuit coupled to said intermediate frequency resonant circuit.

3. In a receiving system for high frequency electric waves, a mixer circuit having an input circuit tunable over a range of signal frequencies and an output circuit resonant to an intermediate frequency, said mixer circuit including a. photo-electric cell connected intermediate the input and output circuits, a source of light for said photo-electric cell comprising a glow tube and means for periodically varying the intensity of the light from the glow tube at a frequency which when combined with the frequency to which the input circuit is tuned produces the intermediate frequency to which the output circuit is tuned, said last named means comprising an oscillation generator for supplying the glow tube with energizing current.

4. In an arrangement for obtaining a third frequency by combining a first frequency and a second frequency, a. photo-electric cell having an output circuit resonant to said third frequency, and an input circuit, a source of light for said photo-cell. means for impressing upon said input circuit a voltage of said first frequency whereby said voltage is impressed across the photo-cell, and means for varying the intensity of light from said source of light at said second frequency.