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Other / Re: Shrimpers 6925 USB 0048 UTC 23 Oct 2013
« on: October 26, 2013, 0056 UTC »
Yes, 8825 is used by Gander and Santa Maria for the NAT's (North Atlantic Tracks).
Every aircraft has a decoder that's programed to a specific 4 letter 'tones' called SELCAL (Selective Calling)
The first two and the last two of the four tones are mixed (sent at same time like DTMF tones are made of two sets of tones) i.e. AD-HJ
Upon initial HF radio check in with Oceanic Control, we ask for a SELCAL check to make sure the decoder works and if there's propagation. After the controller sends the tones, we get chimes and lights, alerting us that ATC want's to speak with us. After check in, we turn the volume completely down so we don't have to listen to all the chatter and/or static for hours as we cross the Atlantic.
At the 30 degree longitude, we repeat the above for we are entering a different controlled airspace. i.e. Gander, Shanwick, NY, Santa Maria, etc...
The FEDs would love to know who they are, or where they are... QRMing aviation frequencies is not taken lightheartedly! Just look at all the fines the FCC dishes out to those to QRM aviation freqs.
From http://www.selcalweb.co.uk/faq.html#3
How do selcals work?
Each letter of the selcal code corresponds to a frequency in the audio range.
Alpha - 312.6 Hz
Bravo - 346.7 Hz
Charlie - 384.6 Hz
Delta - 426.6 Hz
Echo - 473.2 Hz
Foxtrot - 524.8 Hz
Golf - 582.1 Hz
Hotel - 645.7 Hz
India - not used
Juliet - 716.1 Hz
Kilo - 794.3 Hz
Lima - 881.0 Hz
Mike - 977.2 Hz
November - not used
Oscar - not used
Papa - 1083.9 Hz
Quebec - 1202.3 Hz
Romeo - 1333.5 Hz
Sierra - 1479.1 Hz
The frequencies are not harmonics, thereby reducing interference. The selcal is transmitted using Single Side Band, full carrier AM using an encoder such as the one shown below. Every aircraft HF radio contains a USB transmitter as well as an AM receiver in the same unit. The audio signal from the AM detector is connected to a decoding network that uses PLL (Phase Locked Loops) to identify the incoming signals (although many modern aircraft now have selcal decoders that use DSP circuits to decode the codes without the need for PLL). If the tones match what the aircraft is programmed for then a chime or gong will sound in the cockpit and a light will illuminate on the radio panel to signify which radio (HF1, HF2 etc) received the selcal tone. If the tones do not match then they are ignored and nothing happens
And No, I'm not a boat captain, just an aircraft captain!
Every aircraft has a decoder that's programed to a specific 4 letter 'tones' called SELCAL (Selective Calling)
The first two and the last two of the four tones are mixed (sent at same time like DTMF tones are made of two sets of tones) i.e. AD-HJ
Upon initial HF radio check in with Oceanic Control, we ask for a SELCAL check to make sure the decoder works and if there's propagation. After the controller sends the tones, we get chimes and lights, alerting us that ATC want's to speak with us. After check in, we turn the volume completely down so we don't have to listen to all the chatter and/or static for hours as we cross the Atlantic.
At the 30 degree longitude, we repeat the above for we are entering a different controlled airspace. i.e. Gander, Shanwick, NY, Santa Maria, etc...
The FEDs would love to know who they are, or where they are... QRMing aviation frequencies is not taken lightheartedly! Just look at all the fines the FCC dishes out to those to QRM aviation freqs.
From http://www.selcalweb.co.uk/faq.html#3
How do selcals work?
Each letter of the selcal code corresponds to a frequency in the audio range.
Alpha - 312.6 Hz
Bravo - 346.7 Hz
Charlie - 384.6 Hz
Delta - 426.6 Hz
Echo - 473.2 Hz
Foxtrot - 524.8 Hz
Golf - 582.1 Hz
Hotel - 645.7 Hz
India - not used
Juliet - 716.1 Hz
Kilo - 794.3 Hz
Lima - 881.0 Hz
Mike - 977.2 Hz
November - not used
Oscar - not used
Papa - 1083.9 Hz
Quebec - 1202.3 Hz
Romeo - 1333.5 Hz
Sierra - 1479.1 Hz
The frequencies are not harmonics, thereby reducing interference. The selcal is transmitted using Single Side Band, full carrier AM using an encoder such as the one shown below. Every aircraft HF radio contains a USB transmitter as well as an AM receiver in the same unit. The audio signal from the AM detector is connected to a decoding network that uses PLL (Phase Locked Loops) to identify the incoming signals (although many modern aircraft now have selcal decoders that use DSP circuits to decode the codes without the need for PLL). If the tones match what the aircraft is programmed for then a chime or gong will sound in the cockpit and a light will illuminate on the radio panel to signify which radio (HF1, HF2 etc) received the selcal tone. If the tones do not match then they are ignored and nothing happens
And No, I'm not a boat captain, just an aircraft captain!