Talk:Aircraft Communications Addressing and Reporting System (ACARS)
I am trying to extract bit stream of ACARS signals. What I have found after MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) demodulation is that the output bitstream is something like this: "111111111111111111111100000000000001101000111010001100111111"
The above bit stream is exactly the same in all ACARS signals that are demodulated.
By the way, in the ACARS standard, it is claimed that the header is some thing like 2b 2a 16 16 01 (in hexadecimal) or in bits stream sense: 0010101100101010000101100001011000000001
in the standard it is mentioned that the demodulated bitstream is applied to an NRZI decoding
after I apply NRZI decoding to my pure bitstream it changes to: "111111111111111111111101111111111110100011011000110101011111"
My question is that, where the header is ? No such header exists !!!
Can anyone please help me in this regard ?
does this help ?
See also : http://www.ohio.edu/people/uijtdeha/ee6900_fms_08_acars.pdf
Thanks For your response
But indeed the problem I am facing with is not mentioned anywhere. At first, I have been thinking that my demodulation method is not optimum. Using W61PC card, I have been able to compare my demodulated bits to that of Wavecom. The amazing thing is, the latter was exactly like the former. So there is no fault in the demodulation method. Wavecom, extracts the same bits in the beginning of the burst which I have reported as : "111111111111111111111100000000000001101000111010001100111111"
The problem is , after NRZI operation, no sign of SOH or any other header is observable on the demodulated signal.
I am really confused after spending a month on every possible operation, which would lead me to a possible answer. But unluckily I found nothing.
I think someone with experience in this regard would have a major impact to the solution.
I am looking forward for a kind response on this problem.
Thanks to you all.
I Found the answerrrrrrrrrrrrrrrrrrrrrrrrrrrr !!!!!!!!!!!
You want something done, you've gotta do it yourself!
I can share my result via email request !!!
Info hoarding at this level doesn't make much sense, especially on a wiki where the point is sharing knowledge.
ACARS uses 7 bit chars with odd parity, LSBLower Side Band Modulation transmitted first. After demodulation, 0 means change, 1 means no change.
Raw: ...111110000000000000110100011101000110011111101... Decode: 111110101010101010001101000011010001000000011... Bytes: 11010101 (1 0101011 0x2B) 01010100 (0 0101010 0x2A) 01101000 (0 0010110 0x16) 01101000 (0 0010110 0x16) 10000000 (0 0000000 0x01)
131.825 MHzMegaHertz (MHz) 10^6 Hz channel
Hi, in my area (northern Germany), I'm seeing a lot of activity on 131.825 MHzMegaHertz (MHz) 10^6 Hz.
I can't find that frequency on any list, whether here or elsewhere on the internet.
On the other hand, I can't remember ever having seen any activity on the "New European Channel" on 131.850 MHzMegaHertz (MHz) 10^6 Hz, is there perhaps an error in the frequencies? All other channels seem to be correct (at least the ones I can receive).
I can upload a panadapter picture is anyone wanna have a look.