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NMEA0183 GPS input support

Hi experts,
Does KiwiSDR support use of an external GPS?  I have a multitude of GPS units in my proposed installation environment (a small yacht).  I would prefer to have the KiwiSDR use one of their NMEA0183 datastreams.  I can transport the NMEA0183 over Ethernet if necessary.

sv Zen Again
VK6HSR Marine Mobile currently in the UK


  • It doesn't, but help me understand why you would want that capability. Do you have decent Internet access on your yacht such that we could make incoming connections while you were MM? That would be awesome!

    But also awesome would be making connections via WiFi while you were anchored in, e.g., the Marquesas or something. I'll add the NMEA0183 capability just for that! Please let us know what you're thinking.

    John, ZL/KF6VO

    p.s. Are you doing MM WSPR or anything like that currently?

  • Hi John,
    Thanks for your rapid reply.  I would like NMEA0183 capability since we already have several GPS devices aboard, some of which have externally mounted antennas and provide NMEA0183 outputs (and muxes - see below).  For example our chartplotter and our AIS.  Others have internally mounted antennas but they lose lock more easily than those with external antennas.  Boat owners dislike drilling holes, especially to duplicate antennas!

    But there's more.  NMEA0183 doesn't stop at GPS input.   Boat NMEA0183 (and NMEA2000) networkds carry additional data which could be made available via KiwiSDR.  From inside the boat that's speed, course, CoG, SoF, depth, water temp etc).  From outside the boat that's nearby traffic from AIS, radar picture etc.

    Currently one needs deep pockets to have >2400bps internet access at sea.  Higher bandwidth is coming with Iridium's Next constellation and probably others, but they'll probably be expensive initially.  Nevertheless I do see the awesomeness.  Hence my like of questioning!!!  :)

    Connection when anchored with WiFi connectivity would certainly be possible.  Twill be a few years until we get to the Marquesas!  I'm hoping you can add NMEA support soon...

    PS Unfamiliar with WSPR so will do some research.  Will be MM around the UK during "summer".

  • Hi Mike,

    I have just a passing knowledge of the NMEA stuff from running MarineTraffic station #3219 here in Tauranga, NZ. I was specifically interested in what on the Kiwi you wanted a NMEA-based GPS input to drive.

    The Kiwi's built-in GPS does two things. Mostly importantly low level GPS position/time solutions calibrate the receivers main oscillator so the frequency scale is accurate (it can be off due to manufacturing variation in the oscillator crystal or its temperature drift). Additionally the GPS will set the Kiwi time-of-day clock which needs to be within a few seconds for things like the WSPR decoder extension. This is normally done with NTP using sources over the Internet which of course may not be available. You can also use a GPS solution to populate the lat/lon configuration fields on the admin page. 

    Now an external input can't do the calibration function because the NMEA timestamp doesn't have enough resolution (and there is too much jitter in the serial communication method). It would work fine for setting the time-of-day. So unless I'm missing something I think having a NMEA input is of limited value. Except of course it keeps you from having to attach yet another GPS antenna on the yacht. A better solution might be to use an active 3.3V GPS splitter on an existing antenna cable. Of course a lot of Kiwis get by with not using the GPS at all.

  • Hi again John,
    Sounds like I can get by initially without connecting anything to the Kiwi GPS input.  If so I'll buy one and start playing!

    By the way, one of the things I like about the Kiwi is its multi-channel capability.  Standard marine HFs are single channel with limited, slow, sequential channel scanning.  The ability to do sequential scanning on multiple channels would be a big safety plus.  I think the Kiwi will also be much lower power.  One of signal types worthy of scanning is DSC.  Any plans to offer DSC decoding capability?
    Thanks for your assistance.

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