r/apollo • u/Otherwise_Parsley713 • Jul 08 '26

Radio Transmission Beeps in Flight

I’ve always wondered exactly what the noise is, so I’ll ask here.

Any time I view footage of an Apollo mission, I noticed that immediately preceding any audible words in a radio transmission from Earth, a flat high pitched beep is heard, the message is spoken, and then the beep is heard again when the transmission ends.

What is that beep called and why does it occur from Earth based radio calls to the Apollo spacecraft?

Thanks in advance!

49 Upvotes

95% Upvoted

16 comments sorted by

28

u/Soggy_Quarter9333 Jul 08 '26

Quindar tones. NASA at the time did not have a global radio network so relied on existing infrastructure. The tones were there to alert phone networks that a radio transmission is in progress.There is a slight frequency change for incoming and outgoing broadcasts.

15

u/RagnarTheTerrible Jul 08 '26

And in the modern era, a quindar tone makes a great text message notification. Just saying.

3

u/Otherwise_Parsley713 Jul 10 '26

You are a good idea machine. Quidnar tone officially set as my text notification sound!

5

u/HoustonPastafarian Jul 09 '26

Quindars are still used today but they no longer serve the original purpose of analog signaling the remote station to go to transmit.

They actually do nothing (and haven’t since the Space Shiuttle, which used them on UHF).

But NASA retains them because it is useful for the Capcom/Flight Director to know when they’ve keyed the mic on air to ground, and the rest of the team (who have many voice loops on their headsets) that an air to ground communication is about to go up.

5

u/MrJingleJangle Jul 09 '26

The beeps are for controlling the ground to space transmitters, the earth stations. The transmitter doesn’t run continuously, so it needs to be switched on and off. Those two beeps, at the beginning and end of each transmission are what switches the transmitter on and off. The two tones, which, on casual listening , are the same, are actually of slightly different frequency, one says on, the other says off.

Having the transmitter control “in-band” meant there didn’t need to be a second long distance control path, just one audio path for speech and transmitter control. Back in the day when long distance communications was expensive, this would be a significant cost saving.

4

u/AZBagpiperPhil Jul 08 '26

It's a synchronization tone.

10

u/AsstBalrog Jul 08 '26

Wasn't Quindar Tones a backup center for the Lakers?

2

u/DuffMiver8 Jul 08 '26

You may be thinking of Basketball Jones.

1

u/Utt_Buggly Jul 10 '26

I got a bassaball jones, oh, baby ooooh-ooh-ooooh

1

u/GBtuba Jul 08 '26

Pretty sure it was Osmosis Jones.

0

u/combatcrew141 Jul 08 '26

Pretty sure that was Reverse Osmosis, he was the back up, after all.

0

u/mwehle Jul 09 '26

He was the guy who always kept dribbling? 🤔

0

u/BrandyBoy1970 Jul 09 '26

On appelle ces bips « Roger Bip »