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Old 17-08-2017, 18:41   #1
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No GPS signal reaching M-802

When my Icom M-802 was installed it was connected into the boat's GPS system and it worked fine. At some point it stopped working and therefore the DSC will not be effective or not work at all. I want to fix this problem.

Can anyone tell me what the signal on the wires from the GPS should look like? This would help me track down the problem.

Or could some setting in the M-802 have been changed?

Any help would be appreciated.

FYI, I'm not an electronics guru so try and keep it simple.

Cheers.
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Old 17-08-2017, 19:13   #2
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Re: No GPS signal reaching M-802

What the wire looks like or what the signal looks like?
The cable has a BNC connector on one end and probably bare leads that tie into your GPS at the other.
The signal is NMEA 0183.
The only setting that I recall is "GPS detail" or something like, that controls how many digits are displayed.

The GPS unit might output at different speeds. The M802 needs "low speed" (4800 baud). If you at some point changed the baud rate to "high speed" (38400 baud) to match a new chart plotter or AIS or something, then it would be at the wrong speed for the radio. Just a guess.

Personally, I am getting vexing RF interference from the GPS, so I know too well what the signal sounds like.
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Old 17-08-2017, 20:56   #3
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Re: No GPS signal reaching M-802

One of the reasons I hate Microsoft is because they removed the very helpful and free hypertext program from Windows after XP. It allowed you to monitor NMEA data on a laptop.

Unfortunately, the process is kind of geeky. You will need to disconnect the two NMEA input wires from the 802, connect them to pins 2 (+) & 5(-) of a nine pin serial cord, connect the serial plug into a serial/usb converter, load the drivers for the converter, find the right com port, then set the monitoring program (hpertext, Opencpn, gpsdiag,etc to the right baud rate (4800) and com port, and look at the data. If you see data, then work on the 802 settings. If you don't see data, check the settings for source GPS output.

If you feel like getting more geeky, hook a scope across the two wires and you will see little square waves dance across the screen if there is data flowing.
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Old 17-08-2017, 22:31   #4
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Re: No GPS signal reaching M-802

Quote:
Originally Posted by donradcliffe View Post
One of the reasons I hate Microsoft is because they removed the very helpful and free hypertext program from Windows after XP. It allowed you to monitor NMEA data on a laptop.
.....
putty works very well for monitoring serial feeds. Be sure to setup the COM port and baud rate correctly.

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Old 17-08-2017, 22:32   #5
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Re: No GPS signal reaching M-802

don, hypertext is available from MS as a free download.
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Old 18-08-2017, 12:04   #6
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Re: No GPS signal reaching M-802

Assuming your GPS is working on other devices it almost has to be a bad connection or a changed radio setting. Check the VHF manufacturer for how to set/change the GPS baud rate. Most systems use the low setting 4800. I don't think you need to read the signal on the wires to see if there is one causing current pulses.
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