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Old 01-09-2013, 10:06   #16
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Re: NMEA Problem

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Originally Posted by goboatingnow View Post
didn't I read somewhere that some Standard radios need pull-up resistors on the NMEA interface? dave
Yes, some of the early Standard Horizon VHF/AIS radios didn't source enough current to reliably be read by other NMEA devices. Each "listener" on the NMEA circuit eats a bit if current. The quick & dirty solution was to put in a pull-up resistor to enable a bit more current.

If it's working at all, the wiring is probably correct. But dropping some boats (sentences) sounds suspiciously like some of the data is getting lost &/or garbled. And if you load the signal more by feeding it into OpenCPN as well as the chartplotter, the problem should get worse. But Mark (Colemj) probably has better data than I do on what models had problems.

You might try feeding the signal ONLY to OpenCPN, turn on the window to see the data stream, then connect the signal to the chartplotter as well & see what happens to the OpenCPN stream. Of course, this depends on the quality of the Serial/USB converter into the PC, but it might shed more light on the problem. If the sentences get garbled with the additional loading, then it's a "fan-out" problem & you need pull-up resistors.
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Old 14-09-2013, 16:07   #17
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Just an update, a how-to to share and request for some help....


First I picked up a 9-pin serial connector and a cover to finish it off in Radio Shack. I bought the battery powered powered soldering iron.... it is junk, buy the 30w plug in!

Second, it is possible to connect Open Cpn to NMEA 0183 without a multi-plexer. Just configure multiple ports for Open Cpn to listen to. I had my Garmin Map76 in one USB and the serial to USB connector wired to the AIS feed in another. Just be sure to set different priorities for each connection inside OpenCpn or it will crash.

Third when Open Cpn paints an AIS target, it ages the data. It will indicate how many minutes and seconds since the last update...


This is where I need help!!! The Garmin 440 was considering the AIS target lost after not getting a position update for between 1:45 and 2 minutes. But the radio was sending AIS updates every 2:30 to 2:45.

Does anyone know the NMEA0183 standard for how often AIS targets should be updated??? I know when I call Garmin they will blame the radio and the radio firm will blame Garmin....

Thanks for the assist.
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Old 14-09-2013, 16:31   #18
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Re: NMEA Problem

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Originally Posted by Snore View Post
But the radio was sending AIS updates every 2:30 to 2:45.
Our GX2150 definitely sends updated AIS sentences over NMEA much more frequently than that. Like every couple of seconds. Probably higher than that even.

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Old 14-09-2013, 18:06   #19
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Re: NMEA Problem

Quote:
Originally Posted by Snore View Post
Just an update, a how-to to share and request for some help....


First I picked up a 9-pin serial connector and a cover to finish it off in Radio Shack. I bought the battery powered powered soldering iron.... it is junk, buy the 30w plug in!

Second, it is possible to connect Open Cpn to NMEA 0183 without a multi-plexer. Just configure multiple ports for Open Cpn to listen to. I had my Garmin Map76 in one USB and the serial to USB connector wired to the AIS feed in another. Just be sure to set different priorities for each connection inside OpenCpn or it will crash.

Third when Open Cpn paints an AIS target, it ages the data. It will indicate how many minutes and seconds since the last update...


This is where I need help!!! The Garmin 440 was considering the AIS target lost after not getting a position update for between 1:45 and 2 minutes. But the radio was sending AIS updates every 2:30 to 2:45.

Does anyone know the NMEA0183 standard for how often AIS targets should be updated??? I know when I call Garmin they will blame the radio and the radio firm will blame Garmin....

Thanks for the assist.
Here are the specs for update rate (SOG is Speed Over Ground):

Class-A Position report:
if anchored and SOG <= 3 kts, every 3 minutes
if anchored and SOG > 3 kts, 10 seconds
SOG 0-14 kts, 10 seconds
SOG 0-14 kts and changing course, 3-1/2 seconds
SOG 14-24 kts, 6 seconds
SOG 14-23 kts and changing course, 2 seconds
SOG > 23 kts, 2 seconds

Class-A Static data report every 6 minutes

Class-B position report:
SOG <= 2kts, every 3 minutes
SOG > 2 kts, every 30 seconds

Class-B Static data report every 6 minutes.


So, in some cases there will be 3-minute gaps is AIS transmission. With Class-B the gaps may be longer if there is a lot of other AIS traffic, since Class-B uses "the leftovers".
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Old 14-09-2013, 18:10   #20
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Re: NMEA Problem

Snore,
This is the standard a/o 2006: http://www.svsarah.com/Sarah/Images/...0Intervals.JPG (per Maxsea).
Moving targets should transmit within the 2 minute limit of your Garmin plotter, but not if it is an anchored target or slow moving and you miss a couple of transmissions. I had the same issue with my Raymarine C120 display. The software throws away the target info if nothing is received in 2 minutes. A decent AIS Display implementation should allow you to set the purge time frame. That's why I use my PC display for AIS targets. OpenCPN and most PC-based software allows you to set the inactive and purge timeframe.
So if your Garmin does not allow you to set the purge time for targets I would use OpenCPN on a PC as your principal AIS target display.

John
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Old 14-09-2013, 18:13   #21
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Re: NMEA Problem

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Originally Posted by Paul Elliott View Post
Here are the specs for update rate (SOG is Speed Over Ground):
I read the problem as an NMEA sentence update rate from the SH radio to the Garmin - not as the AIS transmit update rate from a ship.

If the problem really is the Garmin requiring a faster AIS transmit update, then that is a serious problem with Garmin.

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Old 14-09-2013, 19:30   #22
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Thanks, the Garmin is having issues with docked and slow vessels. Since the 2150 radio is updating within the NMEA standards, it is a defect in the Garmin program. Odd that this has not come up before.

It would appear that Garmin should be able to do a software update and hang it on the website for downloading.

Armed with your inputs I will have some solid arguments when I call Garmin in Monday.

Assist is greatly appreciated!!!
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Old 14-09-2013, 23:51   #23
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Re: NMEA Problem

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Originally Posted by colemj View Post
I read the problem as an NMEA sentence update rate from the SH radio to the Garmin - not as the AIS transmit update rate from a ship.

If the problem really is the Garmin requiring a faster AIS transmit update, then that is a serious problem with Garmin.

Mark
I don't see how the SH radio could be causing the problem (as long as it's working correctly). It has dual-channel receivers and spits out the AIS sentences as they are received (delayed a tiny amount by buffering). If one of the receive channels has gone bad that could cause a problem, but the message rate that Snore was seeing didn't sound like that was the problem.

I just installed a Garmin AIS600 transponder, and have a fairly new Garmin chartplotter (this is on my power boat, not VALIS). I've noticed more than a few timed-out targets displayed (the triangle with the 'X' across it). I have AIS alarms disabled, since it seems that the Garmin alarm filters aren't useful for close-crossing situations. I will play with this and see what I discover.

Snore, please keep us updated.
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Old 17-09-2013, 15:30   #24
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Update...


After several phone calls, the Level 1 tech support rep was convinced there was a problem. The issue with getting them to buy-in was that Garmin could not replicate the problem. Apparently a Garmin AIS talking to a Garmin 440S does not have a problem. But when a SH 2150 is talking to a Garmin 440S there is a problem.

What went right? Garmin support is staffed with technically competent staff who know their products and connectivity.

What did not go well? Had to debate that if a product (the GPS) is NMEA 0183 compatible. It should be fully compatible. Even if it is no longer available for sale. That AIS sentences are not done by "AIS" but are governed by NMEA standards.


So now awaiting review by Level 2 support.
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Old 26-09-2013, 17:55   #25
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ARGH!!!!!!!!!!

Called Garmin customer support, they are still awaiting the level 2 or technical support guys to make a decision.....

So continuing to wait....
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