GPS position feed for DSC radio

JumbleDuck

JumbleDuck

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I have a Cobra radio which has for a few years been happily taking a GPS position from the NMEA output of my Matsutec HP-33A GPS/AIS. It took a while to get that working, as it turned out that of the outputs available

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only REM1 was acceptable to the radio.Last year the Matsutec failed, so I bought a new one through Amazon. Unfortunately the new one has a much narrower range of NMEA outputs (I suspect that I have been sold an older model) and none of them

AP Output: AAM, ABP, BOD, BWC, GLL, VTG, XTE, ZDA (4800 baud)
GPS Output: GGA, GSA, GSV, VTG (4800 baud)
AIS Output: VDM, VDO, GGA, GSA, GSV, GSV, VTG, RMC, GLL (38400 baud)​

is accepted by the radio. The only sentences in REM1 which are not in any of the current outputs (as 4800 baud) are DTM, RMB and RMC and which are, respectively, "GPS Datum In Use", "Recommended Minimum Navigation Information" and "Recommended Minimum Specific GNSS Data". Of those, only RMC includes the receiver latitude and longitude (see https://www.gpsinformation.org/dale/nmea.htm#RMC) so it looks to me as if that's what the radio wants, rather than a nice simple GLL (https://www.gpsinformation.org/dale/nmea.htm#GLL).

I have a temporary fix. The old HP-33A had two flaws: it turned itself on (which I can live with) and it lost fix constantly, but the latter seems fixed, for now, by using the GPS antenna which came with the new one. However, I'm not confident that it will make it through the summer, so, to cut a long story short ...

Can anyone suggest or recommend a stand-alone GPS receiver which will transmit NMEA-0183 RMC sentences, or something else acceptable to a Cobra radio, at 4800 baud?
 
JumbleDuck said:
Can anyone suggest or recommend a stand-alone GPS receiver which will transmit NMEA-0183 RMC sentences, or something else acceptable to a Cobra radio, at 4800 baud?
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RMC is a very common sentence for GPSes to emit - as its name says, it's a "recommended minimum" set of data. So I tend to think that not doing so is a quirk of that particular Matsutec firmware, and any GPS puck you buy is highly likely to be suitable. Most of the cheap ones use uBlox chips and they can certainly do RMC.

Pete
 
JohnGC said:
http://www.hobbytronics.co.uk/gps-gp-20u7

You'd need a box for this and you'd also need to check the serial port's compatibility.

Have you emptied your inbox BTW? I was unable to pm you a few weeks ago.
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Thanks. I shall investigate. I have cleaned out my inbox a bit, so fire away!

prv said:
RMC is a very common sentence for GPSes to emit - as its name says, it's a "recommended minimum" set of data. So I tend to think that not doing so is a quirk of that particular Matsutec firmware, and any GPS puck you buy is highly likely to be suitable. Most of the cheap ones use uBlox chips and they can certainly do RMC.
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Thanks to you to.

prv said:
You'd need a power supply too - that unit runs at 3.3v. Perfectly doable, my VHF uses a 5v module with a home-made power supply, just depends whether JD can be bothered making his own kit or wants something complete.
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And to you. I have no objection to rigging up a box and power supply, but I'm due to leave for my annual month on board tomorrow, so it would be easier if there was a receiver available which took in 12V and spat out RMC which I could have sent to meet me somewhere.
 
JumbleDuck said:
I have no objection to rigging up a box and power supply, but I'm due to leave for my annual month on board tomorrow, so it would be easier if there was a receiver available which took in 12V and spat out RMC which I could have sent to meet me somewhere.
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The Evermore SA-320 is often recommended. Its output includes RMC. Around £90.

http://www.evermoregps.com.tw/emt/v...&product_id=22&series_name=Marine&series_id=6

https://www.amazon.co.uk/Marine-Evermore-SA-320-Antenna-Output/dp/B001JDAU4S
 
Most mobile phones receive GPS position I don't know if they can export the data to other devices. Many handheld GPSs can interface with radios though.
 
There may be better options these days but the trusty globalsat br355 does rmc. I've been meaning (for the last 8 years) to fit a switch to allow my radio the choice of that or the plotter for its gps.

If you have a multiplexer or fancy playing with homebrew stuff you could always filter rmc out of your ais feed and output that on another interface at 4800 baud
 
I used an Evermore SA-320 with my Cobra DSC VHF and that worked perfectly. I also had with me my Garmin Oregon 300 which I brought along as a spare, normally using it for hiking, but with the optional NMEA connection running via the USB port it too worked well with the Cobra. Incidentally, the Oregon has a very good anchor watch alarm which I found very useful. A good piece of kit.
 
It's not exactly useful but fwiw my Icom lists in the manual the sentences it accepts. They are RMC, GGA, GNS [whatever that is - a typo?] and GLL.

I'm surprised (as I think were you) that any receiver would insist on only RMC and not accept GLL. Is there a not a manual from Cobra you can consult? Bit of a black mark for Cobra if it's really the case.

I'm also surprised that the RMC is not output by the AIS! Mine (Digital Yacht 2000) outputs RMC, GLL and GGA. Perhaps a firmware update is available. SiRF and Ublox chips certainly output RMC, but if the AIS is Japanese it's probably neither of these (probably Renesas). Still worth asking if a firmware update could fix it without new hardware.
 
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jdc said:
It's not exactly useful but fwiw my Icom lists in the manual the sentences it accepts. They are RMC, GGA, GNS [whatever that is - a typo?] and GLL.
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GNS looks like a posh version of GLL but with information about which constellation (GPS/GLONASS/GALILEO/...) the fix is derived from. See https://www.trimble.com/OEM_ReceiverHelp/V4.44/en/NMEA-0183messages_GNS.html

I'm surprised (as I think were you) that any receiver would insist on only RMC and not accept GLL. Is there a not a manual from Cobra you can consult? Bit of a black mark for Cobra if it's really the case.
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I'm off to the boat now and have a Cobra manual on board, so I'll check.

I'm also surprised that the RMC is not output by the AIS! Mine (Digital Yacht 2000) outputs RMC, GLL and GGA. Perhaps a firmware update is available. SiRF and Ublox chips certainly output RMC, but if the AIS is Japanese it's probably neither of these (probably Renesas). Still worth asking if a firmware update could fix it without new hardware.
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It does RMC at 38400. Matsutec were reluctant to cough up new firmware when the HP-33A was current so I have no great optimism that they'll do so now it's replaced. That may be Plan B, though ...
 
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