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+--- Thread: AIS SR161 data problem (/thread-331.html)
AIS SR161 data problem - cyberhusky - June 9, 2007
Hello
Last week of May we went on a sailing trip with 6 boats on the Ijsselmeer (in the Netherlands).
2 boats used iBook G4 to navigate with MacENC and the latest ENC Charts. Unfortunately the buoys in the Netherlands are so often changed (renamed, moved, removed, new ones etc.) that the ENC charts weren't up to date on 2 places. But there was no problem or danger. In fact the papercharts (dated 2007) were wrong on 1 spot too!
A friend had his AIS SR161 receiver connected via Keyspan High Speed USB to Serial Converter to his G4 iBook.
Only once we saw the Red Dot in MacENC AIS Connection Window jumping to green, but there wasn't enough data to see any boat inside MacENC.
On the AIS SR161 Receiver the data red LED is flashing very fast, but the green LED was just green the same moment as data was sent to MacENC.
Now my Qs:
Is the permament flashing of the red LED correct?
Do AIS receivers only get data when there really is AIS signals or does it receive data from the AIS stations too even if there is no boat, just to tell the AIS receiver that the stations are online?
I checked via Wifi, GoogleEarth and Vesseltracker where ships with AIS are on the way, though in the Ijsselmeer there weren't but the Northsea which was about 15 miles away had several cargo ships with AIS signals!
Do the stations which transmit the AIS signal transmit it only seawards or landwards too?
Thx for clarifying my thoughts.
- J122 - July 9, 2007
radio signals make no distinction between land and sea.... (there might be less interference at sea and therefore the signal might travel further) so signals can be picked up inland as well. As for the led it should be flashing green when there is a conection between the ais and macenc (at least this is what mine does) got an CRTX ais receiver/transponder hooked up to a mini with macenc. You might want to check the baud rate at which the ais is transmitting its data and set macenc accordingly.
- bobetter - July 9, 2007
J122 Wrote:As for the led it should be flashing green when there is a conection between the ais and macenc (at least this is what mine does) got an CRTX ais receiver/transponder hooked up to a mini with macenc. You might want to check the baud rate at which the ais is transmitting its data and set macenc accordingly.Actually, that is only partially true. The green "LED" in the AIS panel of MacENC only flashes in the presence of signal from your AIS receiver, it is NOT a specific indication of a CONNECTION between MacENC and and your AIS, although it is obviously connected if it does flash.
- J122 - July 10, 2007
ok, I have to take your word for it, mine is a receiver/transponder and receives its own signal so is always flashing green...
- bobetter - July 10, 2007
J122 Wrote:ok, I have to take your word for it, mine is a receiver/transponder and receives its own signal so is always flashing green...hmmmm, mine is also a receiver/transmitter (and sometimes a transponder when queried by another AIS system) but is a Class B device, not yet approved for use in the US so I usually have my transmitter turned off. I have, on occasion, turned on the transmitter side for testing and am seeing no change in MacENC behavior when I do. When you say "flashing", I assume you mean it is not a steady green but changes from red or yellow to green in a flashing fashion? Steady green would indicate a constant stream of VDM messages, pretty hard to accomplish :>) or that the last sentence received was a valid VDM (probably your case) rather than some other NMEA sentence.
Have you a link to info about your box? I would be interested in why it would be sending it's own signal as a VDM (the trigger sentence for MacENC's AIS panel LED to go green) rather than a VDO (own vessel, which I believe would not trigger the LED) back to MacENC. Thanks
- GPSNavX - July 10, 2007
Actually the !AIVDO NMEA data sentence is processed by MacENC, just not used. As such the AIS panel icon (LED) will remain green when this sentence is received.
I have seen mixed reports where some AIS transponders filter out their own position report and others leave it in. If the later is the case, simply unchecking "show" in the AIS panel list of targets will turn of its display.
- bobetter - July 10, 2007
GPSNavX Wrote:Actually the !AIVDO NMEA data sentence is processed by MacENC, just not used. As such the AIS panel icon (LED) will remain green when this sentence is received.
I have seen mixed reports where some AIS transponders filter out their own position report and others leave it in. If the later is the case, simply unchecking "show" in the AIS panel list of targets will turn of its display.
OK. I would see that as a potential troubleshooting problem-one could be getting the VDO from your own box and not realize there was a problem with the receiver as MacENC would be indicating proper reception, yes?
- GPSNavX - July 10, 2007
The status icon (LED) on the GPS, Instruments or AIS panel indicates the serial NMEA data connection state. GREEN if NMEA data is being received and interpretted, YELLOW if NMEA data is being received and not interpretted and RED for no data reception. The state makes no determination to the validity of the NMEA data. One should not use the status icon to determine if an AIS receiver is properly receiving the transmissions of AIS transponders. The physical LEDs on the AIS receiver should be used for that. While MacENC currently does not do anything with the !AIVDM NMEA data, a green status icon upon its reception just indicates a good NMEA data connecton, not a valid VHF reception connection to the real-world of AIS transponders. Mixing the two is apples and oranges. A comparison would be a GPS sending out the NMEA data for the UTC, but that does not indicate proper GPS satellite reception.