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Old 04-05-2018, 21:24   #1
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NAIS400 says transmitting but can't be seen

Has anyone has ProAIS show 100% good diagnostics, 100's of received messages, dozens of transmitted messages, VSWR of 2.0:1, yet no one can see you?

My NAIS400 has a separate antenna. I have even disabled AIS on my RS35 VHF, just in case.

I see dozens of AIS targets on my chartplotter.
I have my MMSI programmed (I can view it with ProAIS).
GPS has a 3D fix.
I have software version 040200.01.15.01. Software upgrade to v2.02 fails, log shows it using COM6, but Device Manager shows AIS device has COM5.



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Old 04-05-2018, 21:45   #2
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Re: NAIS400 says transmitting but can't be seen

I've had a different brand AIS do this before. I had 100+ ais targets to 40 miles. tried different vhf antennas. (temp holding it on deck). with and without the spliter to VHF. had a SH VHF with different mmsi near by picking up 100+ targets but not me. proais with good SWR and sent msg tally increasing. no n2k or 183 connections

I left boat and never found out what owner did to fix it. I'm guessing unit but seemed weird.
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Old 04-05-2018, 23:24   #3
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Re: NAIS400 says transmitting but can't be seen

Not familiar with this particular model, but does it possibly have a "silent" mode where it does not transmit? My Vesper does...

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Old 05-05-2018, 04:59   #4
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Re: NAIS400 says transmitting but can't be seen

Jim, yes there's a silent mode. When I enable it, there's a blue LED on the unit that lights. It's normally off so I'm confident that's not the issue. Good idea.
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Old 05-05-2018, 08:23   #5
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Re: NAIS400 says transmitting but can't be seen

VSWR of 2:1 isn’t great, should not be fatal but could signal an antenna issue.

If your PC shows a different comm port from the ProAIS pgm, might you be looking at an obsolete status screen? If ProAIS connects, the PC should show an active port at that time (regardless of what it may call the device, which could be remembered from a previous connection).

How are you checking that it (does not) transmits? Another boat / radio, or Marinetraffic (which may not have a station in your area)?
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Old 05-05-2018, 19:39   #6
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Re: NAIS400 says transmitting but can't be seen

I'm going to get a different antenna and test with that.

I'm using AISPro to "know" I'm transmitting.
- Received Channel A: 395
- Received Channel B: 411
- Transmitted Channel A: 7
- Transmitted Channel B: 5

I have verified several times with multiple other boats that they do not see my boat.

I also have the diag messages, in which I see my own transmission (I think):
!AIVDO,1,1,,,B5NUsHP00>`HJ8URwCsQ3wfUoP06,0*59

I do NOT see my vessel on MarineTraffic, at least recently. there was one hit back on April 4th, in the Bahamas (accurate).
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Old 06-05-2018, 04:18   #7
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Re: NAIS400 says transmitting but can't be seen

I plugged [copy-pasted) your dial message into the decoder at
AIS Online Decoder. AIVDM & AIVDO NMEA Messages
If 367623010 is your MMSI then it is your own report, but seems to have some missing fields. I’d give it a try with a few more sentences.
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Old 06-05-2018, 07:16   #8
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Re: NAIS400 says transmitting but can't be seen

Wow, cool decoder. Thanks!
I think I should have COG and SOG, although I'm docked. And it certainly should have a valid timestamp.
The MMSI is correct, at least.

Still looking for a spare VHF antenna.
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Old 06-05-2018, 19:09   #9
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Re: NAIS400 says transmitting but can't be seen

Quote:
Originally Posted by torrmundi View Post
.....

I have verified several times with multiple other boats that they do not see my boat.

......
Have you asked the other boats to look for you by MMSI instead of by name? Your name and ship details are only broadcast about every 7 minutes. If that message is lost, ie failed to be received, then it can take a long time for your boat name to show up. Your course, speed and MMSI is broadcast multiple times per minute.
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Old 07-05-2018, 04:06   #10
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Re: NAIS400 says transmitting but can't be seen

I have; difficult to get cooperation at sea, but at the dock I can walk over to other boats and verify that there is no AIS target shown at my dock location. Thanks for the timing info.
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Old 07-05-2018, 12:15   #11
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Re: NAIS400 says transmitting but can't be seen

I see two possible realms for the problem to be in:

--in the transmiter: the AIS transmitter is not actually transmitting; insert a directional wattmeter into the coaxial transmission line between the AIS transmitter and antenna; set wattmeter scale to appropriate for a 2-Watt transmitter power; observe wattmeter for indication that the AIS transmitter is delivering power to the antenna (note it may take several minutes to produce a transmission); or, monitor the NMEA-0183 output of a nearby AIS receiver to see if the receiver is copying your transmission and delivering an appropriate AIVDM output to the chartplotter; by nearby, at least a few miles away, not 50-feet away. At 50-feet the transmitter could be transmitting a milliwatt and still be received.

--in the data: the AIS transmitter is actually transmitting; AIS receivers a few miles away are receiving; but the data being sent contains an error or is slightly non-standard, causing the chartplotters associated with those AIS receivers to ignore the data and fail to display it; a recent thread discussed how certain chartplotters were confused if an AIVDM datagram contained a value for heading that was not a valid course over ground. This can occur if the vessel speed is low, e.g., as when tied to the dock, i.e., your test method; a GPS receiver cannot provide reliable course over ground data when stationary.
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Old 07-05-2018, 19:31   #12
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Re: NAIS400 says transmitting but can't be seen

CW: I'll settle right now for a nearby detection; I'd be 100% better off!

Wattmeter idea is good, I'll put that on the list. I've ordered a new Tram VHF antenna so I'll have that soon. And I have an Anritsu Sitemaster so when I get a PL-259 adapter, I'll scan the antenna VSWR from 140 to 180 MHz and see how it looks.

The data looks ok for a docked boat. I've decoded multiple sentences I logged and they all decode ok. Yes, COG and Heading are at "not available" values, but I'm docked, right?

I have found these messages, with successful decodes:
18 Standard Class B Equipment Position Report
24 Static Vdssel Report (with correct MMSI and vessel name)

I found some incomplete messages, but any competent chartplotter would ignore those and continue displaying any correctly decoded content.

Interestingly, but disappointing, is Simrad's 8 day silence on the case I opened, even after providing logs, screenshots, and a detailed description.
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Old 07-05-2018, 19:55   #13
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Re: NAIS400 says transmitting but can't be seen

CW: I've thought about measuring output power of an AIS transmitter, and have concluded it cannot be done without some expensive equipment, e.g. a pulse-measuring RF power meter, or a software-defined radio receiver. I could do a crude test with a detector, a load and an oscilloscope, but I lack that equipment.

An AIS transmission occupies a time slot that is 26.67 msec duration, far too short for a SWR-Watt meter to measure.
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Old 07-05-2018, 20:02   #14
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Re: NAIS400 says transmitting but can't be seen

Quote:
The data looks ok for a docked boat. I've decoded multiple sentences I logged and they all decode ok. Yes, COG and Heading are at "not available" values, but I'm docked, right?
Dunno about that... we broadcast speed and cog when at rest (even if not meaningful), and I suspect that if those two data are not available the message will be ignored by a receiving station... just as you describe.

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Old 08-05-2018, 01:09   #15
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Re: NAIS400 says transmitting but can't be seen

Is the AIS actually receiving a GPS signal? Perhaps it is not and that is the problem.
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