Sunday, March 25, 2012

Test Patterns

Do you remember back in the day, that television stations did not broadcast 24 hours a day? In fact back when we first got a television, the local stations didn’t even broadcast during the middle of the day. I can remember gathering around the TV around a quarter till four in the afternoon; when they would resume their broadcast day with a test pattern that featured a rendering of an Indian head for 15 minutes before the afternoon western serials. Children’s programming was the king of the afternoon then the local evening news at 6, the network news at 6:30, local programming until 8 then three hours of prime time network programming and a short late night local newscast followed by the formal television station sign-off and the United States national anthem then 15 more minutes of that ubiquitous test pattern.

Oh how we hated that test pattern with that smug Native American chief staring off to the right at who knows what while that tone droned on incessantly. It was so boring and we wanted to get on with the fun of the afternoon. The Indian Head Test Pattern was the most common black and white television test pattern. Introduced in 1939 by RCA of Harrison, New Jersey, its name comes from the original art of a Native American featured on the card. The Indian Head Test Pattern became familiar to the large post-war Baby Boom TV audiences in America from 1947 onwards.

Later in life, I learned that the test pattern came from a carefully calibrated camera called a monoscope and served a specific purpose. The test pattern was used to make many typical daily (sometimes hourly) adjustments on cameras, and studio monitors. An experienced broadcast engineer would use the test pattern to make careful adjustments to the TV station’s master monitor. After the monitor was adjusted, a cardboard mounted lithograph of the test pattern, attached to an easel in each TV studio, was videographed by each studio camera during test time. Then the cameras were adjusted to appear identical on picture monitors, by alternately switching between and comparing the monoscope image and the test card image. Such adjustments were made on a regular basis because television system electronics then used hot vacuum tubes, the operating characteristics of which drifted throughout each broadcast day.

Test patterns were broadcast to the public daily to allow regular adjustments by home television set owners and TV shop repair technicians. The same features on the pattern used by the television station engineers were included to facilitate focus and contrast settings, and the measurement of resolution. The circular "bulls-eyes" in the centre and the four corners permitted uniform deflection yoke and oscillator amplitude adjustments for centering, pincushioning, and image size. While all this techie stuff was going on, my brother and I were impatiently waiting for the test pattern to disappear and the fun to begin.

By time I was working in television, the test pattern had all but disappeared. We still had one on a card that we used to adjust the RCA TK-10 black and white camera that was used to create the “supers” and “crawls” that were seen at the bottom of the screen. Yes, I became that techie geek making the adjustment, but we didn’t bore all the kids in the audience by broadcasting it. Also by then, television station’s broadcast days were longer, beginning at 6:45 AM with the local farm show and ending at 1AM after the Tonight Show with Johnny Carson. We did have an electronically generated test signal called "color bars." They can occasionally be seen today. Did you know that we could not broadcast the color bars for over 15 minutes for fear of overheating the final tubes in the transmitters? Oh MY!

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