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Old 19-04-2019, 11:21   #1
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RMC messages lost in NMEA stream

Hi.

I have a USB GPS device - a NaviLock nl-8002u - which I have set to receive GPS, Glonass and Galileo satellites.

When I look in the NMEA stream there are no RMC meassages in OCPN 5 (see attached dump).

But when I look in a simple NMEA moitor program, as well as in the device manufacturer's setup program there are RMC strings present (see the other dump).

I find this a bit interesting...or maybe it's just some setup error on my behalf.
I get a valid position from the other NMEA sentences that are read, though...

B.R.
Magnsu Ohlsson
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Name:	NMEA stream in OCN 5 No RMC sentences.jpg
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ID:	190325   Click image for larger version

Name:	NMEA stream in GPS-NMEA Monitor RMC filtered out.jpg
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ID:	190326  

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Old 19-04-2019, 11:44   #2
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Re: RMC messages lost in NMEA stream

115200 at baud rate?
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Old 19-04-2019, 11:50   #3
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Re: RMC messages lost in NMEA stream

Yes, 115.20 kBaud. Set in COM port properties and both programs.
I have tried other baud rates with the same result...
It's a fast device...
/Magnus
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Old 19-04-2019, 11:59   #4
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Re: RMC messages lost in NMEA stream

What happens if you ignore the checksum?
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Old 19-04-2019, 12:04   #5
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Re: RMC messages lost in NMEA stream

Will try that a bit later tonight...
/Magnus
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Old 19-04-2019, 13:42   #6
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Re: RMC messages lost in NMEA stream

Quote:
Originally Posted by bcn View Post
What happens if you ignore the checksum?
So, now I have tried unticking the cheksum.
Disappointing result though.
Some sporadic RMC sentences get through, as opposed to the stream in the NMEA monitor program where RMC sentences are spouted out three times every second, with checksum enabled.
(Makes sense - the GPS is set up for 3 Hz update rate)

/Magnus
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Name:	NMEA stream in GPS-NMEA Monitor RMC filtered out_2.png
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ID:	190354   Click image for larger version

Name:	NMEA stream in OCN 5 without checksum - sporadic RMC sentence.jpg
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ID:	190355  

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Old 19-04-2019, 17:37   #7
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Re: RMC messages lost in NMEA stream

Quote:
Originally Posted by maohls View Post
So, now I have tried unticking the cheksum.
Disappointing result though.
Some sporadic RMC sentences get through, as opposed to the stream in the NMEA monitor program where RMC sentences are spouted out three times every second, with checksum enabled.
(Makes sense - the GPS is set up for 3 Hz update rate)

/Magnus
Have you tried a more sane update rate of say 1 per second?

You don't need positional updates faster than that except for very special purposes. Heading information at high speed is useful of course but that would come in a different sentance.
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Old 20-04-2019, 02:56   #8
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Re: RMC messages lost in NMEA stream

Quote:
Originally Posted by Moo View Post
Have you tried a more sane update rate of say 1 per second?

You don't need positional updates faster than that except for very special purposes. Heading information at high speed is useful of course but that would come in a different sentance.
Hi.
Sorry!
Lowering the rate to 1 Hz and setting the port to 38.4 kBaud - no difference.
OCPN still doesn't receive the RMC sentences whereas the NMEA monitor program does...
/Magnus

PS. The reason I bought this device was not for the possibility of high update rate, but for being able to receive Galileo as well as GPS and Glonass DS.
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Name:	NMEA stream in OCN 5 at 1 Hz and 38.4kBaud - still no RMC.jpg
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Size:	403.9 KB
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Old 20-04-2019, 03:45   #9
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Re: RMC messages lost in NMEA stream

On which Operating System are you?
Can your use a simple terminal program to hook to the serial port to get an input stream?
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Old 20-04-2019, 03:52   #10
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Re: RMC messages lost in NMEA stream

Quote:
Originally Posted by bcn View Post
On which Operating System are you?
Can your use a simple terminal program to hook to the serial port to get an input stream?
This is a Win10 laptop. I have used two separate NMEA terminal programs and they both show RMC sentences (see dumps in previous posts)...
/Magnus
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Old 20-04-2019, 04:17   #11
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Re: RMC messages lost in NMEA stream

Looking again on your NMEA debug window from OCPN

- why are there broken entries?
- and why are there garbled RMC messages - better: messages preceded by garbage?

And if you try with 4800 or 9600baud?
The Navilock devices are usually pretty well behaving. Have one running here.
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Size:	203.6 KB
ID:	190393  
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Old 20-04-2019, 05:44   #12
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Re: RMC messages lost in NMEA stream

Quote:
Originally Posted by bcn View Post
Looking again on your NMEA debug window from OCPN

- why are there broken entries?
- and why are there garbled RMC messages - better: messages preceded by garbage?

And if you try with 4800 or 9600baud?
The Navilock devices are usually pretty well behaving. Have one running here.
Yes, I noted those few corrupted RMC messages as well as other more obvious erroneous sentences such as "<0x0F>#" on several occurancies.

Backing down to 4800 Baud, 1 Hz didn't change the picture - still no RMC sentences in OCPN. The position is extracted through GGA, GLL and GNS which are received correctly.

Found a clue though!
The attached dump shows the stream, and EVERY RMC line is preceeded by some propriety UBX binary sentence.
Maybe this could cause problems for OPENCPN.
Will try to get rid of that...
/Magnus
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Name:	NMEA stream in NMEA monitor propriety sentence preceeding RMC.jpg
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Size:	260.7 KB
ID:	190396  
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Old 20-04-2019, 07:25   #13
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Re: RMC messages lost in NMEA stream

May you record a bit of that data stream and post here?
We should sure handle crap like that better...
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Old 20-04-2019, 08:15   #14
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Re: RMC messages lost in NMEA stream

Thanks for looking into this - really great!
Here's a small recorded stream - as you see some crap in front of every RMC sentence...

/Magnus

PS. Remove the .doc extension. It's a zip-file, but that seemed to be an invalid file extension DS.
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File Type: doc Recorded_NMEA_stream_Navilock8002U.zip.doc (9.7 KB, 10 views)
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Old 21-04-2019, 01:32   #15
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Re: RMC messages lost in NMEA stream

Hi,

I got something similar to this.

I use the nmea connection to send route Information to the Autopilot.
For that I set the filter for outgoing Messages to RMB and RMC sentences.
This worked great under OC 4.8.8

Now with OC 5.0 I got irregular wrong COG/SOG informations sometimes the right, sometimes totally wrong, sometimes only ------/-------.
Only when started a route (navigate to in the right click menue).
After I investigate the nmea data stream I found out that there was sentences where ALL the NMEA-sentences from my Network where combined and ther always started with the RMC-sentence from OC for the Autopilot.
After changing the filter for the outgoing sentence so that only the rmb sentence was send this was fixed and the Autopilot gets the route information too (rmb is enough for the pilot, the manual says he need rmc).

Regards

Andreas
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