On January 26th of 2013 I came across some HF ATC (Air Traffic Control) traffic on 5600 LSB. It was interesting to listen to and it sounded like the ATC controller was in or around New York from what I could tell of her accent. I did a little research and could not find the frequency but I did find out what the tones that accompanied the transmission were. According to “RonR” at LiveATC.net the tones are called “Sel Call.” That set of tones are used to call a specific aircraft operating in the HF bands in oceanic airspace. The tones are specific for each aircraft. The communication system on the aircraft records the tones to memory and then if ATC is calling using their tones they are alerted to the call. If they did not have the tones then the pilots would have to constantly monitor the frequency. I have included in this post about five minutes of the audio I recorded. It is interesting to listen to. I have also included some links HF ATC frequencies.
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