Electronic Era (1920–1960)Optoelectronics & Electronic Display

Farnsworth Electronic Television & Image Dissector

US 1,773,980

All-Electronic Television, Continuous Photo-Cathode, and Magnetic Raster Scanning

Inventor(s)Philo T. Farnsworth

Grant Date1930-08-26

Filing Date1927-01-07

LocationSan Francisco, California

Farnsworth's 1930 image dissector: a photoemissive plate, a magnetic raster, and a pinhole anode. No Nipkow disk. He conceived it at 14, looking at a plowed Idaho field, and reduced it to practice in a San Francisco loft in 1927.

USPTO PDF

Engineering Analysis & Physical Principles

How It Works: Step-by-Step Mechanical & Physical Breakdown

Baird and Jenkins television was a Nipkow disk or a mirror drum: 30 to 60 lines, flicker, noise. Farnsworth, at 14 in a plowed Idaho field, pictured an electron beam doing the furrows. Electrons have no flywheel, so line count is an electronics problem, not an rpm problem.

The Core Breakthrough Mechanism

Lenses focus an optical image onto a silver-cesium cold photoelectric plate at the front of a vacuum tube, knocking loose millions of electrons in exact proportion to the brightness of each point in the image. High voltage pulls this full electron cloud toward the back of the tube. Two pairs of electromagnetic coils create shifting magnetic fields that sweep the entire electron cloud back and forth across a microscopic pinhole aperture in a rapid raster pattern. The electrons passing through the pinhole form a continuous video signal that is amplified and transmitted over radio waves to a cathode ray tube (CRT) display screen.

Interactive Real-Time 3D Physics Simulation

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Detailed Component Architecture

1Continuous Photo-Cathode Plate

A flat silver-cesium plate that converts photons into a free electron cloud.

Operates via the photoelectric effect ( $E_{kinetic} = h\nu - \Phi$ ). Brighter parts of the image liberate higher current densities $J(x,y)$ , creating a true 2D electron image in the vacuum.

19th-C. Term: Continuous photoelectric surfaceModern: Photoelectric image sensor / Photo-cathode

2Orthogonal Magnetic Deflection Coils

Electromagnetic coils sweeping the electron image in a 2D sawtooth raster.

Horizontal coils produce a high-frequency linear sweep ( $15.75\text{ kHz}$ for NTSC); vertical coils produce a $60\text{ Hz}$ frame sweep. Lorentz forces ( $\vec{F} = q \vec{v} \times \vec{B}$ ) deflect the electron stream with zero mechanical inertia.

19th-C. Term: Deflecting coils energized by alternating currentsModern: Magnetic deflection yoke / Raster generator

3Target Anode & Scanning Aperture

A metal shield with a microscopic pinhole aperture.

Isolates a single pixel area of the electron image at a time, converting spatial image brightness $I(x,y)$ into a time-varying video current $i(t)$ .

19th-C. Term: Target with scanning apertureModern: Aperture pixel sampler / Electron multiplier

Governing Physical Equations & Principles

Einstein Photoelectric Current Generation

J(x,y) = \eta \cdot \frac{e}{h\nu} I_{optical}(x,y)

The spatial current density of emitted electrons is linearly proportional to the optical irradiance of the image focused upon the photo-cathode.

Lorentz Force Magnetic Beam Deflection

\vec{F} = q (\vec{E} + \vec{v} \times \vec{B}), \quad r_{gyro} = \frac{m v_\perp}{q B}

Orthogonal magnetic fields steer the high-velocity electron stream across the scanning aperture at relativistic speeds with zero moving parts.

Why It Still Matters

Every camera still reads a scene as a time-series of lines. CMOS pixels replaced the dissector plate; the raster idea did not. CRTs are gone from living rooms, not from the sampling theorem that made them, and LCDs, work.

Legal Claims Decoder (2 Numbered Claims)

Compare dense legalistic claims directly with decoded plain-English functional specifications.

Claim #1Independent Master Claim

Verbatim Historical Legal Text

“The method of television transmission which consists in forming an electrical image of the object to be transmitted, and scanning said electrical image across an aperture to produce a television signal, substantially as described.”

Plain English Engineering Translation

The historic master claim covering the method of all-electronic television: forming an electron image in a vacuum and scanning it electronically across an aperture.

Key Protected Innovations:

All-electronic television transmissionElectron image formationElectronic raster scanning across an aperture

The Historical Bottleneck

Baird and Jenkins television of the mid-1920s was a spinning Nipkow disk, 30 to 60 holes, a lamp, and a lot of flicker. Mechanical inertia set the line count. You could not spin a disk fast enough for a picture a newsreel audience would sit through.

Why Prior Art Failed

•Nipkow disks were dim, noisy, and limited to tens of lines.
•Mirror drums drifted out of sync and shattered.
•Zworykin's early iconoscope work at Westinghouse was real but not yet a closed electronic camera-plus-receiver system in public.

The Breakthrough Insight

“Age 14, Rigby, Idaho, 1921: a plowed field looked like a scan. Electrons have no flywheel. Farnsworth told Justin Tolman, his chemistry teacher; Tolman kept a 1922 blackboard sketch that later won an interference.”

Patent Wars & Legal Litigations

Vs. David Sarnoff, Vladimir Zworykin, and RCAInfringement Challenge

Rival Claim & Defense:

RCA argued Zworykin's iconoscope and the 1923 filing predated Farnsworth's reduction to practice.

Litigation Conflict:

Interference No. 64,027. Tolman's sketch and testimony dated conception to 1922. The Patent Office awarded the electronic-scanning claims to Farnsworth in 1934. Sarnoff, who preferred not to pay outsiders, had to write a royalty check.

Final Resolution & Judicial Outcome:

RCA licensed Farnsworth. Commercial US television still waited on the 1941 NTSC standard and the war. Farnsworth's company never became the RCA of cameras.

After the Grant

Farnsworth sold to ITT, fought depression and drink, and lived to see the 1969 moon walk on a set that owed him a license. He told his wife that this, at least, made the whole fight worth it.

Civilizational Impact

Once the scanner had no moving parts, line counts could rise with electronics instead of rpm. News, advertising, and national politics moved onto a raster.

Historical Fact

7 September 1927, 202 Green Street, San Francisco: the first image was a straight line. Pem Farnsworth was in the room. The dollar sign they later joked about scanning was a lab gag, not the first transmission.

Further Context

The image dissector has no charge-storage target, so it needs a lot of light. Studio cameras went to iconoscopes and then orthicons for that reason. The patent is the electronic scan, not the most sensitive photocathode.
Farnsworth was 20 when he filed. Investors had backed a high-school idea with cash. That is rarer than the plow story.