Quindar tones

The Quindar tones are beeps that NASA used in space flights in radio traffic, transmitting systems on Earth by remote control on and off, so that the may Capsule Communicator ( Capcom ) communicate with the crews of space ships. In this case, a so-called in-band signal is used to simulate a push-to- talk button ( PTT ), as commonly found in hand-held radio devices. The sounds are since the Gemini program in use and were also used in the Space Shuttle program. The general public, they were known by transfers during the Apollo program.

Need

Thus, the Houston-based Mission Control Center could remain in contact 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 via leased lines, the operation was very expensive at that time. NASA was faced with the task of setting up two systems for controlling the transmitter - one to transmit the audio signals from Capcom, and one for the control signal of the PTT button - but instead it was decided to combine both systems into a single order to keep operating costs low.

Implementation

The two tones are generated by the name of its manufacturer Quindar system. Both are pure sine tones of 250 ms duration. The start-up has 2,525 Hz and signaled to press the PTT key. The end tone is 2,475 Hz slightly deeper and signals when the PTT button. The sounds are produced by a 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 whose passband extends approximately from 300 Hz to 3,400 Hz. In above or below pitch the signal would not fit under special circumstances in this transfer area and could not be transferred.

Typical misconceptions

It is often misleadingly assumed that the first Quindar sound comes from the earth, while the second is generated by the transmitters of the astronauts in space. This confusion arises because many Earth -to- space transmissions are initiated by the flight control center and answered by the astronauts. In this order, the Capcom press the PTT button that triggers the startup sound, then he speaks. In the end he releases the PTT button, whereby the end tone is sent, followed by the response of the astronauts.

If you suspect that they are the Quindar tones each of the opposite side, the end of a transmission signal, similar to a " Roger " Beep, which is used by many half - duplex radio - relay stations, it is also a misunderstanding.

Origin of the name

The Quindar tones are named after the company Quindar Electronics, Inc.. This was confirmed by Glen E. Swanson, a historian of the Johnson Space Center NASA and author of Mission Transcript Collection, and Steve Schindler, an engineer for linguistic analysis of the Kennedy Space Center NASA:

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

" Quindar tones, named after the manufacturer of the equipment for the production and detection of sound, are actually used for the switching on and off of the transmission facilities in the various ground stations. "