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Receive and Decode DGPS on 306 KHz

Here's a video on Youtube......


  • I found an open source DGPS decoder that could be the basis for a Kiwi extension. But it's written in assembler for the Motorola DSP56k (ugh). So transliterating that into C is going to be extremely tedious and a nightmare to debug. If anyone has a better source (open) please let me know. I don't know how the decoders in the usual suspects (Fldigi, Multipsk) were developed.

  • None of those things is an DGPS digital receiver. They are just packages that take serial (NMEA) output from your DGPS or GPS hardware device and process the ASCII data. I'm looking for the part that is upstream of that: an MFSK demodulator that uses the DGPS protocol.

  • I've had that project in my bookmarks for a while now. It's an example of a working low speed MSK demodulator/modulator.

    What I really need is a complete, working, open source DGPS decoder.

  • MultiPSK does a fair job with decoding DGPS.

    the author of the software contact is on the attached image.

  • Doesn't matter. None of those closed-source applications are going to allow someone to use their algorithms in an open source work. None. Zero.

  • Hi John,

    There is a small but functional program called KG-DGPS, showing the actual GPS corrections. A couple of years ago the author "KG" JJ0OBZ made a whole series of mostly freeware and  well designed speciality decoders, but then unfortunately stopped other developments and support due to QRL workload or conflict of interest. Probably one of the Japanese users can find out more about the status of these programs and whether they can be considered abandon-ware or are now permitted to be included in other software. 

    On the other end of the non professional users spectrum there is "Amalgamated DGPS" which can run a large number of parallel decoders covering the complete DGPS LF band and shows a list and map display of received stations and time lines. The cost of the latter is  less than 20 usd.

    Probably many users do have a wish to have certain decoders included in KiwiSDR and perhaps we could have some voting to show which are most requested.

    Which brings me to a more general point about digital mode decoders: one may wonder if it is worth your valuable time and effort to create rather complex demodulators/ decoders for inclusion in KiwiSDR, if affordable third party alternatives are easily available. Such a decision and choice of additional decoders of course remains  with you.

    PS: KG-HFDL is an excellent HFDL (Arinc635) decoder with integrated map mode, hf tuning, database look-up and selcal (Arin714A) decoding and certainly beats PC_HFDL and similar programs. Sometimes I have used it on long flights to monitor surrounding traffic out of VHF or TCAS range.
  • The KG software is working under wine on linux. I'm having trouble figuring out the buttons on KGFAX, but have it decoding the image. The buttons are ??? instead of text. Probably don't have a Japanese font in the WINE Font library. The KGdgps software is excellent and easy to use. Thanks for posting the links to the software.
  • Some time ago I have written code for DGPS demodulation and decoding, see

    It is based on this thesis

    In fact I thought before to add a DGPS decoder to the KiwiSDR. What would be interesting is to use a polyphase channelizer like this one
    and decode in parallel all 0.5 kHz spaced DGPS channels in the 12kHz wide IQ data stream.
  • @Christoph Wow, I did not realize that's what HFMonitor did. I looked at it briefly once. But since the Readme and Wiki were pretty sparse I didn't go any further. I had also found Tim's thesis some time ago, but found it very frustrating that many of the figures were illegible.

    I see from main.dox a mention of a spectrum display for EFR|DCF77|MSF|NavyMSK. Is this an IQ display with a carrier-recovery PLL? The later would be very useful for my IQ display which doesn't have one and suffers from uncontrolled phase rotation unless you manually adjust the clock just right.

  • jksjks
    edited April 2018
    @Benson So one of the ideas with the Kiwi is that simple versions of decoders should be built-in in keeping with the idea that the software should be self-contained. I think a lot of users struggle with getting VACs to work or even understanding the concepts involved. And all you have to do is read on here, or the web, about the problems people have getting external software to work. is filled with people having problems getting software for their RTL-SDR dongles to work. It's just a terrible situation.

    Kiwi decoders will never compete with the functionality of existing standalone programs. But that's not the point. It's all just an experiment to see how far the web-based, all-in-one concept of the Kiwi can be pushed.

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