#1 2015-07-19 22:57:19

PA3BAS
Member
Registered: 2014-12-01
Posts: 20

Trying to decode ATIS

I am thinking of using a micromodem to decode ATIS-signals. This is upsed in maritime VHF communication to send your ships callsign after you depressed the PTT-button. From what i can find it is simular to aprs/packet, but uses other tones for high and low (2100 and 1300 hz). Is that possible with libAPRS?

Here is Python program wich is doing what i am trying to do in Arduino...

http://www.qsl.net/pa2ohh/13atisrx.htm

Last edited by PA3BAS (2015-07-19 23:00:23)

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#2 2015-07-29 20:06:16

IW3IJQ
Member
Registered: 2015-07-27
Posts: 13

Re: Trying to decode ATIS

Hi!

In AFSK.h you can try change MARK_FREQ, SPACE_FREQ and others parameters.

I don't know exacly how to decode ATIS.

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#3 2015-07-30 00:48:33

PA3BAS
Member
Registered: 2014-12-01
Posts: 20

Re: Trying to decode ATIS

Thank you for the answer. I will try and see what comes in. Next step is to decode the incoming bytes.

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#4 2015-08-05 20:17:16

markqvist
Administrator
Registered: 2014-12-01
Posts: 112

Re: Trying to decode ATIS

Really interesting! Is the ATIS frame format the same as APRS? You should be aware that APRS uses a 16-bit CRC checksum at the end of each packet, and if this is not correct, the APRS firmwares will not output the packets. You can deactivate this check in the source code to have it output whatever it thinks it's decoding, but this will still be dependent on a 0x7E (01111110) as frame delimiters.

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#5 2015-09-28 19:54:49

PA3BAS
Member
Registered: 2014-12-01
Posts: 20

Re: Trying to decode ATIS

I now have a setup i can use to do some testing. Meanwhile i also found the 'rulebook' for ATIS, which is derived from DSC (digital selective calling).

http://www.gmdss.com.au/ITU%20DSC%20tech%20spec.pdf

I found the place where to change the 2 frequencies for MARK and SPACE (afsk.h), but i have no clue on how to change the 'magic'.

Maybe one of you clever guys here can help a bit?

Last edited by PA3BAS (2015-09-28 20:26:05)

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#6 2015-09-28 21:10:07

PA3BAS
Member
Registered: 2014-12-01
Posts: 20

Re: Trying to decode ATIS

Oh, one more thing: what should i change where to be able to see the raw input without any error checking? I first want to be able to check that it works, then try to implement the error checking.

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