The Indian Head Test Pattern became familiar to the large post-war Baby Boom TV audiences in America from 1947 onwards; it would often follow the formal television station sign-off after the United States national anthem. The Indian Head was also used in Canada, following the Canadian national anthem sign-off in the evening. This test pattern was later used by Venezuelan TV channel Venevision, in conjunction with the RMA Resolution Chart 1941, in the mid and late 70's before the Venezuelan anthem (Gloria al bravo pueblo).
The Indian Head pattern could variously be seen: after sign-off but while the station was still transmitting; while transmitting prior to a typical 6 AM formal sign-on; or even during the daylight morning hours on newer low budget stations, which typically began their broadcast day with midday local programs around 10 or 11 AM.
During the late 1950s the test pattern gradually began to be seen less frequently, after fewer sign-offs, on fewer stations, and for shorter periods in the morning, since new and improved TV broadcast equipment required less adjusting. In later years the test pattern was transmitted for as little as a minute after studio sign-off while the transmitter engineer logged required FCC-USA/Industry Canada transmitter readings, and then turned off the power.
Towards the end of the Indian Head TV era, there was no nightly test pattern on some stations, typically when automatic logging and remote transmitter controls allowed shutdown of power immediately after the formal sign-off. After an immediate transmitter power off, a USA or Canadian audience, in lieu of the Indian head Test Card and its sine wave tone, heard a loud audio hiss like FM radio inter-station noise and saw the video noise colloquially called "snow," indicating the absence of a broadcast signal on the channel. With the scheduled end of USA high power analog broadcasting on February 17, 2009 (low power USA TV stations may continue analog broadcasting), "snow" may be the only thing visible when an old analog TV is turned on without a digital TV converter.
When USA broadcasters transitioned to color television, the SMPTE color bars superseded the black-and-white test pattern image. In Sweden the Indian head was used in test transmissions from the Royal Institute of Technology from 1948 until November 1958 when it was replaced by the Sveriges Television test card.
The primary and critical Indian Head Test Pattern was not itself a card. Rather, it was generated directly as a monochrome video signal by means of a monoscope camera.
An RCA TK-1 Monoscope Camera is a 19-inch rack-mounted chassis, which contains electronic circuits needed to operate a glass cathode ray tube housed inside of an anti-magnetic steel shield. The cathode ray component is a TV-camera vacuum tube known as a monoscope, because it videographs only one still image, the test pattern. The tube has a perfectly proportioned copy of the test pattern master art inside, permanently deposited as a carbon image on an aluminum target plate. This perfect copy allowed all of the studio and control room video picture monitors, and home television sets, to be identically adjusted for minimum distortions such as ovals instead of circles. When the monitor or TV set was correctly adjusted to show test pattern circles, the received picture's aspect ratio was exactly three units high by four units wide. The 3 by 4 standard was chosen by the National Television System Committee (NTSC) for analog television, so that film movies would be compatible with TV broadcasting. 3 by 4 is the same aspect ratio used by 16mm and classic 35mm motion picture film frames.
Only after the monitors were adjusted was an actual Indian Head Test Card used. A cardboard mounted lithograph of the test pattern was typically attached to a rolling vertical easel in each TV studio, to be 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 also broadcast to the public daily to allow regular adjustments by home television set owners and TV shop repair technicians. In this regard, various features in the pattern 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.
The test pattern was usually accompanied by a 1,000 or 400 hertz sine wave test tone, which demonstrated that the TV aural receiver was working. If the tone was pure-sounding rather than a buzz or rattle, then transmitted speech and music would not be distorted. 400 Hz is somewhat less annoying for technicians to hear for extended work periods.
An actual Indian Head Test Card was only of secondary importance to television system adjustment, but many of them were saved as souvenirs, works of found art, and inadvertent mandalas. By contrast, nearly all of the hard-to-open, steel-shielded, vacuum glass monoscope tubes were junked with their hidden Indian Head Test Pattern target plates still inside. The monoscope target plates were also small, a few inches in size, while the showy camera test cards were sized on the order of 1-½ feet by 2 feet, making them natural keepers for picture-framed wall display.
The original art work was completed for RCA by an artist named Brooks on August 23, 1938. The master art was improbably discovered in a dumpster by a wrecking crew worker as the old RCA factory in Harrison, NJ was being demolished in 1970. The worker kept the art for over 30 years, and then used the Internet to locate and sell it to a test pattern collector.
As of 2008, most television stations in the United States no longer sign off overnight, instead running infomercials, networked overnight news shows, syndicated TV re-runs, or old movies, but the Indian Head Test Card persists as a symbol of early television. It was even sold as a night-light (from 1997 to 2005 by the Archie McPhee company), reminiscent of the times when a fairly common late-night experience was to fall asleep while watching the late movie, only to awaken to the characteristic sine wave tone accompanying the Indian Head Test Pattern on a black-and-white TV screen.