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+--- Thread: Noob question: NMEA gps out to vhf marine radio? (/showthread.php?tid=1815)
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RE: Noob question: NMEA gps out to vhf marine radio? - svkatielee - 2019-07-03
(2019-07-02, 10:41 AM)Melipone Wrote: Thanks! I thought maybe as you only mentioned 2 wires I'd need something for 4, but I suppose the VHF doesn't need to send any data to the Pi. Will give it a try!
Before I bought a Class B AIS, I connected the NMEA out of radio at 38400 baud to my opencpn to have the AIS on screen. I had a separate adapter for each direction because of the baud rates.
RE: Noob question: NMEA gps out to vhf marine radio? - skyeyedoc - 2019-07-03
(2019-07-03, 12:34 AM)svkatielee Wrote:That's interesting. So, the class B AIS (a transceiver, I'm presuming?), receives GPS at a lower baud rate from OpenPlotter, and provides AIS target charting to OpenPlotter at the higher baud rate? If so, I'd not considered that duplex at different speeds was do-able.(2019-07-02, 10:41 AM)Melipone Wrote: Thanks! I thought maybe as you only mentioned 2 wires I'd need something for 4, but I suppose the VHF doesn't need to send any data to the Pi. Will give it a try!
Before I bought a Class B AIS, I connected the NMEA out of radio at 38400 baud to my opencpn to have the AIS on screen. I had a separate adapter for each direction because of the baud rates.
Am I understanding correctly?
Elliott
RE: Noob question: NMEA gps out to vhf marine radio? - svkatielee - 2019-07-03
(2019-07-03, 11:15 AM)skyeyedoc Wrote:(2019-07-03, 12:34 AM)svkatielee Wrote:That's interesting. So, the class B AIS (a transceiver, I'm presuming?), receives GPS at a lower baud rate from OpenPlotter, and provides AIS target charting to OpenPlotter at the higher baud rate? If so, I'd not considered that duplex at different speeds was do-able.(2019-07-02, 10:41 AM)Melipone Wrote: Thanks! I thought maybe as you only mentioned 2 wires I'd need something for 4, but I suppose the VHF doesn't need to send any data to the Pi. Will give it a try!
Before I bought a Class B AIS, I connected the NMEA out of radio at 38400 baud to my opencpn to have the AIS on screen. I had a separate adapter for each direction because of the baud rates.
Am I understanding correctly?
Elliott
Almost but not quite. Almost all Class B AIS transceivers have a GPS built in, so their output is NMEA 0183 at 38400 baud, They output both their AIS sentences and their GPS sentences. The UN-official standard for GPSs is they output (on the OUT+ and OUT- (or GND)) the GPS sentences at 4800 baud. My older Standard Horizon radio had an AIS receiver built-in, but no GPS. So I had to give it GPS sentences at 4800 to the NMEA IN+ and GND at 4800 and it output the AIS on NMEA OUT+ and GND at 38400. So in this case 3 wires were used.
Some devices have NMEA IN+ and IN- and OUT+ and OUT- so 4 wires (not duplex at different bauds on the same pair.) Usually the -(minus) is actually ground. RS232 is actually -12v=1 and +12v=0, but works ok (abused Recommended Specification(RS)) with +5v and 0.0v )
AIS has a potential of a lot more data thus it needs the higher baud rate to get all the data transfered. (I saw 538 ships on AIS as I rounded Singapore a while back. )