NASA actually uses QUINDAR tones for in-band signalling.
And they are only transmitted by ground control.
The first tone (2525 Hz) turns on the remote transmitters.
The second tone (2475 Hz) turns off the remote transmitters.
These tones are 250 ms of pure sine waves and being so close together can be notched out with a single filter.
73 - Bill KA8VIT
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From: FT-857@... on behalf of Russell Stringfield rs12240@... [FT-857]
Sent: Wednesday, December 12, 2018 8:38 AM
To: FT-857@...
Subject: RE: [FT-857] vk1od Roger Beep installation into FT857d
?
In Europe, I believe, it takes a tone to open the repeater.? Same thing that we hear when NASA talks to the ISS, etc.
Russ
