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Old 12-10-2020, 15:14   #1
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Icom M802 SSB - Garmin GPSMAP 78 NMEA Transfer

I have recently purchased a Garmin GPSMAP 78 (78), with the intention of having that unit transfer NMEA 0183 data to my Icom 802 SSB (802), so that the LAT/LONG information appears on the 802's display and is available in the event that I have to initiate a DSC emergency call. I plan on attaching the 78 at the nav table close to the 802.

I decided to go with the 78 because it was a newer model GPS receover, would provide me with a small color display at the nav table and because I presumed that it would provide me with a similar method of installation and operation that others seem to have had on this forum with the 78's predecessor the GPSMAP 76. So far, however, no joy.

My first issue came down to how to connect the 78 to the 802's BNC cable (center wire and shield). I have finally figured out that using the Garmin data cable which has red, black, brown (data out) and white (data in) wires, I connect the 78's wires as follows: red to power (+), black to ground (-), brown to the center wire of the BNC cable, and the shield on the BNC cable to the same ground as the black (-) wire. The 78's white wire is not connected to anything. Hopefully, someone can confirm that this is the correct connection procedure.

The main problem, however, seems to be in being able to send the correct NMEA 0183 information from the 78 to the 802. I have tried all manner of variations but can't seem to get the right combo. The 78's menus allow me to select the GPS signal as NORMAL GPS vs. (WAAS/EGNOS & Demo Mode) and the Interface as (NMEA In/Out vs. (Garmin Spanner, Garmin Serial, Text Out, RTCM). The issue, however, seems to be how or if to select the following choice(s) under the sub-menu NMEA Sentences: GSA,GSV on/off; WPL,RTE on/off; Garmin Proprietary on/off. In talking to ICOM they have confirmed that the three NMEA sentences that are required by the 802 are $GPRMC, $GPGGA and $GPGLL.

Can someone who has a 78 configured as I want to configure mine, confirm what their settings are on that unit so that the 802 shows LAT and LONG on its display. Or if they have a GPSMAP 76 (or know a heck of a lot more about this area than I do) tell what those settings might be.

Finally, this is the second attempt to get LAT/LONG info to the 802. The first was using a newer Garmin 19 GPS antenna. Garmin concluded that this antenna/receiver might not be able to communicate with the 802 due to some hardware/software issue. I had the 802 checked by ICOM service several months ago (my boat had been hit by lightning last year), and the service center advised me the 802 was not damaged, so presumably the LAT/LONG input is working on the 802. So I don't think that is the problem.

Bottom line, can I get the 78 to work, or do I just go buy an old used GPSMAP 76 and be done with it?

As always, thank you for your assistance.
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Old 12-10-2020, 15:43   #2
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Re: Icom M802 SSB - Garmin GPSMAP 78 NMEA Transfer

This thread maybe helpful to you
https://www.cruisersforum.com/forums...ems-27992.html

It seems the 802 will only accept the GGL statement. I tried several GPS unit at the time and I finally found a cheap GPS pluck that provide the GGL statement.

I don't recall the make or model except it was from China and very cheap - it was a decade back now!
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Old 12-10-2020, 23:43   #3
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Re: Icom M802 SSB - Garmin GPSMAP 78 NMEA Transfer

if the garmin 19 is nmea 183 it should work. I have used one before. you need the resistor inline to drop the baud rate back to 4800. (comes in box)

the 802 is picky and it only accepts 1 gps sentence I think. the 78 may not send it. not sure.

the handheld should be set to nmea in / out. just turn everyone on. it's not going to hurt to have extra stuff. and see what happens.
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Old 13-10-2020, 23:41   #4
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Re: Icom M802 SSB - Garmin GPSMAP 78 NMEA Transfer

The 802 requires the GGA sentence at a baud rate of 4800 v3.01.

After going through hell I managed to get my Icom 412 and 802 radios to accept GPS input from an old Garmin 12 that cost me $20, it is used for the radios only and not nav.

The Garmin 12 suffers from the date rollover error so reports a date around 2001, but DSC apparently doesn't use date, only time and position which are accurate.
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Old 13-10-2020, 23:46   #5
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Re: Icom M802 SSB - Garmin GPSMAP 78 NMEA Transfer

I think the Garmin 12 default baud rate is 9600, i had to set it to 4800 in menu to work with the radios.
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Old 14-10-2020, 07:19   #6
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Re: Icom M802 SSB - Garmin GPSMAP 78 NMEA Transfer

Thanks to all who have answered. I presume no one sees a problem with the physical wiring I have proposed, so I shall proceed on that assumption.

As for the Garmin 19 antenna, Garmin told me that with a recent software upgrade to that product, it is possible that the antenna will not communicate properly with the 802. So, I sent that unit back and bought the 78.

As far as the 802 is concerned, ICOM has advised that the 802 accepts RMC, GGA and/or GLL sentences for LAT/LONG, not just GGA. But 4800 baud is the proper speed and version 3.01 is the appropriate version, though some have seen success using an earlier version as well.

So, I am going back to the boat tomorrow and based on my reading and further conversations with ICOM and Garmin, I plan on turning off all extraneous sentences that are being sent to the 802. That means turning off the GSA, GSV, WPL,RTE and Garmin Proprietary sentences the 78 is equiped to send. That should leave only RMC, GGA and GLL sentences (among a few others), being sent to the 802. The ICOM techs I talked to indicated that too much data can also sometimes confuse the 802 and thus it won't accept what it gets and thus not show any LAT/LONG info. So cutting down on the number of sentences it is receiving should help...we hope. Seems strange, but they should know their product.

I also plan on making sure that the precision of the minutes being sent by the 78 corresponds to what the 802 requires/displays. Specifically, that the number of minute data points for LAT/LONG correspond to what the 802 is looking for. The 802 if memory serves, only uses two data points for minutes (for example, 038.17.98 N), while the 78 broadcasts up to four (038.17.9814 N). So cutting the 78's minutes settings back to two, may help. We shall see.

Finally, push to shove, I shall set up the 78 to send its data to an autopilot, which setting only sends a limited number of sentences, one of which (RMC), is one of those that the 802 accepts for LAT/LONG. Maybe that will work.

Beyond that, I am plumb out of ideas. So, if anyone has more of a clue, or one more strategy I might employ, I am all ears.

Needless to say, thanks very much for your help. I really appreciate the assistance. On the positive side, I am really learning a lot about NMEA 0183. Too bad pretty much everything is now using the NMEA 2000 standard.
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Old 14-10-2020, 07:34   #7
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Re: Icom M802 SSB - Garmin GPSMAP 78 NMEA Transfer

we had the same problem with our Raymarine Axiom Pro/Icom 802. I tried everything, literally everything. The LAT/LONG showed perfectly fine until I turned on the chartplotter, then it disappeared. Raymarine finally told me to try hooking up our old Raystar 125 GPS directly to the radio and use the GPS ony for the radio.

We've done that and now it works. The best solution is probably to buy a cheap GPS puck and hook it directly to the radio
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Old 14-10-2020, 08:15   #8
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Re: Icom M802 SSB - Garmin GPSMAP 78 NMEA Transfer

Quote:
Originally Posted by gchabs View Post
Thanks to all who have answered. I presume no one sees a problem with the physical wiring I have proposed, so I shall proceed on that assumption.

As for the Garmin 19 antenna, Garmin told me that with a recent software upgrade to that product, it is possible that the antenna will not communicate properly with the 802. So, I sent that unit back and bought the 78.

As far as the 802 is concerned, ICOM has advised that the 802 accepts RMC, GGA and/or GLL sentences for LAT/LONG, not just GGA. But 4800 baud is the proper speed and version 3.01 is the appropriate version, though some have seen success using an earlier version as well.

So, I am going back to the boat tomorrow and based on my reading and further conversations with ICOM and Garmin, I plan on turning off all extraneous sentences that are being sent to the 802. That means turning off the GSA, GSV, WPL,RTE and Garmin Proprietary sentences the 78 is equiped to send. That should leave only RMC, GGA and GLL sentences (among a few others), being sent to the 802. The ICOM techs I talked to indicated that too much data can also sometimes confuse the 802 and thus it won't accept what it gets and thus not show any LAT/LONG info. So cutting down on the number of sentences it is receiving should help...we hope. Seems strange, but they should know their product.

I also plan on making sure that the precision of the minutes being sent by the 78 corresponds to what the 802 requires/displays. Specifically, that the number of minute data points for LAT/LONG correspond to what the 802 is looking for. The 802 if memory serves, only uses two data points for minutes (for example, 038.17.98 N), while the 78 broadcasts up to four (038.17.9814 N). So cutting the 78's minutes settings back to two, may help. We shall see.

Finally, push to shove, I shall set up the 78 to send its data to an autopilot, which setting only sends a limited number of sentences, one of which (RMC), is one of those that the 802 accepts for LAT/LONG. Maybe that will work.

Beyond that, I am plumb out of ideas. So, if anyone has more of a clue, or one more strategy I might employ, I am all ears.

Needless to say, thanks very much for your help. I really appreciate the assistance. On the positive side, I am really learning a lot about NMEA 0183. Too bad pretty much everything is now using the NMEA 2000 standard.
I have the gpsmap 78 and have used it to connect to openCPN but not the 802. The following is from memory, but hopefully helps.

Black and shield should be the same. I prefer to use black, and leave the shield disconnected.

One potential issue. The garmin serial port is RS232, and the 802 is RS-422. Usually they can be connected together. Sometimes to get rs232 and rs422 to talk to each other you need to reverse the polarity. So, black on the garmin to the center conductor, and brown to the outer.

https://www.stratusengineering.com/r...tronics-power/

If you need to reverse the polarity, it should still be ok to ground the black wire (and the center pin on the 802) and apply power to the red wire. Notice on the above link RX+ on the rs422 side is grounded.

If you have a computer with an rs232 port connecting the gps to that is straightforward and you can use a program like putty to verify what sentences are being sent and that the speed is 4800 (it should be)

The gpsmap 78 does support the correct GGA sentence:
https://support.garmin.com/en-US/?fa...mea&tab=topics

Interface needs to be set to NMEA in/out. In the submenu I turned everything else on. There is also an autopilot mode and that might need to be activated as well to get all the required sentences. By default only a limited number are sent and autopilot mode activates everything the gps supports.
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