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Re: So can someone tell me a bit more about GW Dataplex?

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  • Benjamin
    Still I m waiting for someone to comment on my post, and share their GW Dataplex knowledge with me.
    Message 1 of 2 , Nov 2, 2012
      Still I'm waiting for someone to comment on my post, and share their GW Dataplex knowledge with me.

      --- In dxsoft@yahoogroups.com, "Benjamin" <BenHutchinson_3@...> wrote:
      >
      > I got plenty of this digital mode on the maritime bands. I live in Seattle Washington, and use a ICom PCR1000 receiver. They usually encounter fading so that means the signal is taking an ionospheric bounce path, so the signal sources for GW Dataplex clearly are not from near Seattle. But there's no mistake, it's GW Dataplex. I recognize the sound from an audio file I've heard on a radio listening forum.
      >
      > Also, on RadioReference forums, one person linked to some much needed info that they found on DXSoft Yahoo group here.
      >
      >
      >
      > "Re: [dxsoft] mode suggestion
      >
      > Henrik,
      >
      > I believe only the Wavecom decoders for government use can decode GW Pactor
      > itself.
      >
      > The channel free markers which can be decoded by Hoka and Skysweeper are not
      > really very interesting - mainly because all they have is a single byte ID
      > and no-one has properly correlated these to known coast stations.
      >
      > Here is all I have on it if anyone is interested in taking it further:
      >
      >
      > Globe Wireless Marker Decoding
      > ==============================
      >
      > Globe Wireless provides HF marine traffic via coast stations.
      > They use a proprietary modem which sounds similar to Pactor.
      >
      > Protocol Description
      >
      > Unfortunately, the protocol they use on HF is a proprietary one for which
      > few decoders are available. The signal uses at least two different
      > modulations: 100 baud, 200Hz shift synchronous FSK and PSK.
      >
      > Globe Wireless seems to send at least 4 distinct kinds of traffic from their
      > stations:
      >
      > *Channel Free Marker
      > ARQ Data (speculative)
      > Selcall or FSK data (speculative)
      > PSK data
      >
      > *Decoding the Channel Free Marker
      > There is a repetitive channel free marker broadcast when a channel is idle.
      > This is in 100bd 200Hz shift FSK.
      >
      > The total number of bits sent in the channel free marker is 231.
      > The first 98 bits compose this header:
      >
      > 10100101001000000011100010100011000111110110110000 110101001110110100101111110010\
      > 111100101111001011
      >
      > Following this, an 8 bit quantity repeats 6 times - a form of FEC.
      >
      > The byte corresponds to the following table:
      >
      > 0x47 HLF, Seoul, South Korea
      > 0x49 KEM, Nikolski, Alaska, USA
      > 0x4e VCS, Halifax, Nova Scotia, Canada / VCT, St. Johns, Newfoundland,
      > Canada
      > 0x5d KEJ, Honolulu, Hawaii, USA
      > 0x5e CPK, Santa Cruz, Bolivia / VCT, St. Johns, Newfoundland, Canada
      > 0x5f A9M, Hamala, Bahrain
      > 0x63 9HD, Malta
      > 0xc3 XSV, Tianjin, China
      > 0xc9 VIE, Darwin, Australia / ZLA, Awanui, New Zealand
      > 0xcc HEC, Bern, Switzerland / 9MG, Penang, Malaysia / LFI, Rogaland, Norway
      > 0xd2 ZSC, Capetown, South Africa
      > 0xd7 KPH, San Francisco Radio, San Francisco, California, USA / VJS, Perth,
      > Australia
      > 0xd8 WNU, Slidell Radio, New Orleans, Louisiana, USA
      > 0xdb KHF, Agana, Guam
      > 0xdc KFS, Palo Alto, California, USA
      > 0xdd LSD836, Buenos Aires, Argentina
      > 0xde SAB, Goeteborg, Sweden
      > 0xe3 8PO, Bridgetown, Barbados
      >
      > There are other stations with unknown bytes.
      > E.g., 0x3b possibly Pt. Reyes, California, USA.
      > More work is needed to match all the coast stations.
      >
      >
      > Credit to Ben Mesander
      > http://tiki-lounge.com/~ben/radio/gw.html"
      >
      >
      >
      > However I have some questions about some of the info. Is the 6 repeat FEC bytes a repeat of the station id byte? Or what byte is it repeating?
      >
      > Also even if you have 98 bits, that is NOT divisible by 8. So I must ask just HOW are the bytes divide up out of this stream of 98 bits? The person who had this info seems to know enough to know that 98 bits compose the header. But he seems to have gotten something wrong. he claims it's 98 bits out of 231 bits. However I know the 231 bit count is bogus. I myself have used a free program called ABox2 (which allows you to make all kinds of audio DSP processing devices with simple block-diagrams) to FSK demodulate it into a bit stream and I counted 152 bits by putting the resulting text file (each line is one bit) into MS Excel and noting how many lines it takes (easily read off of the numbers on the rows of MS Excel).
      >
      > So I need a more accurate description if I'm to make a decoder for the channel marker GW Dataplex signal.
      >
      >
      > PS: It's not a matter of Globe Wireless stations as people like to say it seems, but rather of ships, coastguard stations, etc, who are using Globe Wireless hardware for their digital communications.
      >
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