Quindar tones

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The quindar tones are tones that the NASA used in space flights in radio communications to transmission facilities on the ground by remote control on and off so that the capsule communicator can (Capcom) with the crews of spaceships communicate. A so-called in-band signal is used to simulate a push-to-talk button (PTT button), as is usually found on handheld radios . The tones have been in use since the Gemini program and were still used in the space shuttle program . They became known to the general public through broadcasts during the Apollo program .

need

To enable the Houston- based Mission Control Center to stay in touch with the astronauts as they flew to the moon and back, NASA used several earth stations , including the Goldstone Deep Space Communications Complex in California and the Canberra Deep Space Communication Complex in Australia, as Part of the Manned Space Flight Network . These earth stations were connected to Houston by dedicated lines , which were very costly to operate at the time. NASA was faced with the task of building two systems to control the transmitters - one to carry the audio signals from the Capcom and one for the control signal of the PTT button - but instead it was decided to combine both systems into a single one to do the To keep operating costs low.

implementation

The 250 ms long start tone with 2,525 Hz, followed by an end tone with 250 ms at 2,475 Hz

The two tones are generated by the Quindar system named after its manufacturer. Both are pure sine tones of 250 ms duration. The start tone has 2,525 Hz and signals that the PTT button has been pressed. The final tone is slightly lower at 2,475 Hz and signals the release of the PTT button. The tones are generated by special equipment in the flight control center and decoded by detectors within the various earth stations.

The choice of tones makes it possible to use the same frequency band as the human voice in the telephone system, the pass band of which extends from approximately 300 Hz to 3,400 Hz. If the pitch was higher or lower, the signal would, under certain circumstances, no longer have fitted into this transmission range and could not have been transmitted.

Typical misunderstandings

It is often misunderstood that the first quindar sound comes from Earth , while the second is generated by the astronauts' transmitters in space. This confusion arises because many earth-to-space transmissions are started by the air traffic control center and answered by the astronauts. In this order the Capcom presses the PTT button, which triggers the start tone, then it speaks. At the end he releases the PTT button, which sends the end tone, followed by the astronaut's response.

The assumption that the Quindar tones signal the end of a transmission to the other side, similar to a “Roger” beep that is used by many half-duplex radio relay stations , is also a misunderstanding.

Origin of the name

The quindar tones are after the company Quindar Electronics, Inc. named. This has been confirmed by Glen E. Swanson, a historian at NASA's Johnson Space Center and author of the Mission Transcript Collection , and Steve Schindler, a speech analysis engineer at NASA's Kennedy Space Center :

"Quindar tones, named after the manufacturer of the tone generation and detection equipment, are actually used to turn on and off, or 'key', the remote transmitters at the various tracking stations."

"Quindar tones, named after the manufacturer of the devices for generating and detecting the tones, are actually used to switch the transmitters on and off in the various ground stations."

- The Story Behind the Beep . In: The Mission Transcript Collection . January 1, 2006. Retrieved August 17, 2009.

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