Hawes Mechanical Television Archive by James T. Hawes, AA9DT
Two-Color Television Systems, Part 3

Two-Color TV History

Two-color TV, highlights. In television, two-color reproduction has a long history. Here are some highlights...

Gould 3D. In 1932, Leslie Gould patented a two-color, three-dimensional television system. This system reproduced a 360-degree view of an enclosed, finite space. The effect was something like viewing a moving Mercator projection, including naturalistic contours. The system wasn't anaglyphic, and didn't require viewing glasses. [Gou., Figs. 1 & 4]

See the Gould 3D patent drawing, right. Items (231) are the orange-red and teal lamp tubes. A revolving arm (215) carried these tubes as it rotated behind the scanning drum (219). The drum and arm rotated in opposite directions. The Gould TV drum (219) was cylindrical. The viewer could watch a realistic image from the front, back or sides of this TV! A translucent screen outside the drum was optional.

 Patent art: 3-D, 2-color TV receiver by Leslie Gould (mechanisches Farbfernsehen: 3-D, Empfänger mit zwei Farben)
Gould's 3-D, two-color monitor. Drum #219 offers a 360°, cylindrical viewing area!    

Alexanderson. Ernst Alexanderson invented a two-color, NTSC-compatible TV system in 1940. This system used a color wheel that rotated before the CRT at 1,800 rpm. [Abr., 266-267] In 1933, Alexanderson had patented a two-color television system that used two CRTs in the receiver: Each with a complementary color filter. [Ale.] If CBS had adopted either Alexanderson system, the company could have avoided its monochrome-compatibility problems. Alexanderson's systems would have accurately reproduced flesh tones. The flicker would have been minimal.

 Photo: Ernst F. W. Alexanderson
Alexanderson
Photo: Guillermo González Camarena
Camarena

Camarena. In 1963, Guillermo González Camarena demonstrated his version of two-color, field-sequential NTSC. He proved his system in broadcasts from Mexican station XHGC. Camarena's system could use either a color wheel or a color CRT display. In either case, the electronics were vastly simpler than those for NTSC color. The standard vertical sync signal triggered color field changes. [Sol., 48, 71]

NRI Schools. For decades, NRI Schools® (National Radio Institute) offered superb correspondence courses in electronics. Budding technicians performed lab experiments on the famous Conar® kits and prototyping stations. Most of the test equipment also bore the dependable Conar brand. In the late 1960s, one NRI course may have included a two-color color wheel TV kit. (At the Antique Radios.com forum, the author has read about such a kit.) The kit would have been an NTSC-compatible color receiver. It would have included a phase selector, a demodulator, and a synchronized color wheel. Keep your eyes open. This very rare kit might just turn up on eBay!



Two-color NTSC

Two-color mode. Compatible-color NTSC itself includes a two-color mode. The two-color mode is part of the original, 1953 NTSC specification. Since then, due to production costs, few TV receivers have used this mode. Yet the two-color mode remains part of the transmitted NTSC signal. The two NTSC colors are orange and teal. Two-color transmission is the reason why NTSC has a broadband chroma signal that we call “I.” European PAL receivers provide no such broadband, two-color mode. In fact, the PAL color gamut is narrower than the NTSC gamut.

I & Q. In NTSC, signal I is one of two chroma signals. The I-signal represents most of the essential colors. This signal describes an axis that runs between orange and teal (so called “flesh tones”). The other color signal is Q. Signal I has a bandwidth roughly three times that of signal Q. Signal I is 1.5 MHz wide, vs. only 500 kHz for Q.

 NTSC method of sending full color on two subcarriers I and Q.
NTSC uses two subcarriers (I & Q) to convey full color.

Together, signals I and Q describe large details in all three primary colors. As details become smaller, the Q signal tops out. Afterward, the I chroma signal carries on alone. Medium-scale details, then, appear as mixtures of the I-colors, orange and teal. Meanwhile, the greens and purples of the Q signal don't affect medium details. Eventually, even the I channel tops out. For instance, no color appears in small picture details. In fact, the eye can't discern color in small details. NTSC conserves bandwidth by broadcasting these small details in monochrome.

Col-R-Tel® in Two Colors

With only a few modifications, cyan and red Col-R-Tel seems quite possible. A two-color set would have far less flicker than does the three-color model. Yet the two-color version would still render flesh tones (the most important colors) perfectly. Eliminating flicker is a significant upgrade. Most viewers would appreciate the modification.

Change summary. First, the color wheel changes: We must replace the six-segment, RBG—RBG color disc. The new disc also has six segments, but the six color wedges alternate between red and cyan (or orange and teal). The electronic changes might not be any more difficult than a Col-R-Tel installation. The main change is the addition of a two-pole, double-throw switch. Here's the step-by-step approach...


Assembly Procedure

After examining of the Col-R-Tel schematic and operating instructions, the author pieced together the modification procedure below. [Col., 3, 7 & 8]

  1. Replace the three-color, six-segment disc with a two-color, six-segment disc.

  2. Connect a wire to the cyan (-R-Y) tab on phasing coil L2.

  3. Cut the blue and green (B-Y and G-Y) lines between coil L2 and V3. (On the drawing, points with the marking "X.") From now on, we'll call the transformer side of the cut the "input wire." We'll call the V3 side of the cut the "output wire."

  4. In a convenient location near the cut wires, mount DPDT switch S1. In later steps, you'll wire the switch in series with the blue and green color-phase lines from phase coil L2. When wiring the switch, you might need to add wire. To avoid noise, keep the wiring as short and direct as possible.

  1. To the top-left tab, connect the blue (B-Y) signal input wire.

  2. To the top-right tab, connect the green (G-Y) signal input wire.

  3. To the center-left tab, connect the blue (B-Y) signal output wire. This wire will actually carry the cyan (C) or blue (B-Y) signal. Note that the drawing labels this wire "C or B."

  4. To the center-right tab, connect the green  (G-Y) signal output wire.

 Mechanisches Farbfernsehen: Modifications to Col-R-Tel phase selector.
  1. To the bottom-left tab, connect the -R-Y signal input wire. The -R-Y signal is an inverted red signal that comes from the bottom transformer phase. Another name for inverted red is cyan.

  2. Leave the the bottom-right tab open.

  1. Rewire the commutator jumpers, following the Commutator Jumper Diagram, right: Connect all contacts that select the same color (red or cyan). Avoid shorts between red wires and cyan wires or contacts.

  2. Between the Col-R-Tel commutator and connector P6, cut the green wire. See the drawing Col-R-Tel 2-Color Commutator Wiring, right. The cut occurs at the "X" on the drawing. (This cut isolates the green-select diode at tube V3. The new, two-color circuit switches between the other two sections of this tube.)

  3. Tape the cut ends of the green wires.

  4. Set the new switch S1 to its bottom (two-color) position.

  5. Run a regular Col-R-Tel setup as in the manual. The next two steps summarize the process.

 Mechanisches Farbfernsehen: Col-R-Tel commutator jumpers for 3/c and 2/c pictures. Commutator Jumper Diagram

Mechanisches Farbfernsehen: Modifications to Col-R-Tel commutator. Col-R-Tel 2-Color Commutator Wiring (Mouse over for 3-color wiring.)
  1. With a picture on the screen, adjust your TV for the sharpest picture. Use these controls...

    2. • Fine Tuning: For sharpest picture
    • Contrast: Increase • Brightness: Increase

  2. With a picture on the screen, adjust the Col-R-Tel hue and saturation controls: (The chassis labels identify these controls as Color Lock and Color Gain.) Continue adjusting until you achieve the best possible flesh tones.



Bibliography
Abramson, Albert. The History of Television, 1880 to 1941. Jefferson, North Carolina: McFarland &
Company, 1987.
https://is.gd/EETJ79
(Access on February 22, 2022.) •Re: Superb, well-balanced international history of television technology, by author with engineering background. This first volume traces television development from its nineteenth century roots to beginning of World War II. Second volume extends story to 2000, with special emphasis on videotape. These books read more like database than narrative. Extensive second book loses some luster, but is nonetheless valuable reference.

Alexanderson, E.F.W. Colored Television Apparatus. U.S. Patent 1,988,931. File date: May 2,
1933.Issue date January 22, 1935. Assignee: General Electric Company.
https://patents.google.com/patent/US1988931A/en
(Access on February 23, 2022.) •Re: U.S. patent for Alexanderson's two-color television camera and monitor. Of particular interest: Figs. 1 & 4.

Color Converter, Inc. Col-R-Tel Converter (Assembly, instruction,maintenance, & troubleshooting
manual). Columbia City, Indiana: 1955.
https://www.earlytelevision.org/pdf/colortel_manual.pdf
(Access on January 30, 2022.) •Re: Manual for Col-R-Tel, 1955 predecessor of Spectrac & Scope. Col-R-Tel could reproduce 3 primary colors. Schematic in manual details switch connections that require modification for two-color operation.

Gould, Leslie A. Television Apparatus and Method [3D patent]. U.S. Patent 2,058,681. File date
June 16, 1932. Issue date October 27, 1936. Assignee: Radio Inventions Inc.
https://patents.google.com/patent/US2058681A/en?oq=U.S.+patent+2%2c058%2c681
(Access on January 30, 2022.) •Re: U.S. patent for Gould's 3D, two-color television camera and monitor.

Solomon, Leslie. “Simplified Mexican Color TV.” Electronics World, July, 1964.
https://worldradiohistory.com/Archive-Electronics-World/60s/1964/Electronics-World-1964-07.pdf
(Access on February 2, 2022.) •Re: Description of Camarena's color television system using two primary colors. Successful tests over station XHGC in Mexico.



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Page Directory

On this page...
Two-Color TV History

2-color NTSC

2-color Col-R-Tel

Assembly

Schematic


On related pages...
What is Two-Color TV?

Col-R-Tel vs. Spectrac

TV System Flicker Comparison

2.5-Color TV

Gould Television: 3D from the Great Depression

Gould 3D: Could It Work?

Gould 3D: Camera & Monitor Formulas

The Lost Creations of Leslie Gould

Spectrac: Color for a Monochrome World



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•Portraits of Alexanderson & Camarena are stock photos. (Retouching, cropping, & vignetting by the author.)