A special message to Quindar tone connoisseurs
Posted in Here's the Tower on 6 Feb 2019 3 min read
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Quindar Tones - Here's the Tower
Episode 38

A bit of administrative business this week. The sound that starts and ends every episode of this program is sometimes called the NASA beep or the com switch, but its real name is the Quindar tone.

Every episode of Here’s the Tower – and the episodes of my previous show Snuggling with the Enemy that I made with with my friend Karin – they all start and end with these tones.

Like many other people, I erroneously believed that this beep occurred between when Mission Control spoke and when the astronauts spoke; like a walker talkie, the beep was like the static sound that signaled when the other party’s transmission was complete.

I have since discovered, while watching old Apollo documentaries, that the tone was used in signaling the transmitters around the world that relayed communications to and from the spacecraft. Therefore, the tone did not occur when the astronauts talked amongst each other, for example, during space walks or on the surface of the Moon.

I have heard thousands of Quindar tones over several decades as a part of my enthusiasm for the Gemini, Apollo and Shuttle missions, but suffice it to say that I have always misunderstood their purpose.

Furthermore, I never noticed that there are actually two different tones.

There is an intro tone at 2,525 Hz which signals the engagement of the push-to-talk button and an outro tone that signals the release at a slightly lower frequency of 2,475 Hz.

The difference between these two frequencies is only noticeable if you really listen for it, but the relay stations could tell them apart. These particular tones were chosen because they’re in the same frequency range as human voices and were therefore easy to broadcast through the same channels that Mission Control used to talk with the astronauts.

The tone I have been using in dozens of episodes of this and my previous podcast has been identical at the beginning and end of each episode, which has been incorrect.

The sample I have been using has been a fairly dirty recording of an outro tone that I seem to remember copying from the audio of an early Shuttle mission.

I apologize to anyone who has been disturbed by my use of an outro tone at both the beginning and end of each episode. From now on, you’ll hear the proper intro and outro Quindar tones in future episodes of Here’s the Tower.

As a side note, Quindar tones are 250 milliseconds in length. That’s a quarter of a second. So the beginning and ending Quindar tones combined have subtracted a full half second from every episode. That’s a full 19 seconds of our valuable time together that has been wasted listening to beeps.


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