Problem with obtaining position from laptop on VHF

[adam.lazarski]

Good day, I’m a little confused thus I cannot obtain position on VHF Icom M422 from laptop through UART module by RS232 interface. Connections are prepared properly Tx in UART on Rx in radio and Rx in UART on Tx in radio. Gnd is also connected. Radio displays NO POSITION. I reach navigational data on laptop through WiFI by UDP Server. Position server is stated on iPhone which of course works in the same network as laptop. Position, COG and SOG is obtained on laptop with no problem. Laptop sends sentences $IPRMC and $IPGLL which are accepted by radio (according to VHF manual).

Moreover VHF is fine Because it obtain position from ploter Garmin GPSMap 182
with no problem. I connected Garmin to laptop by UART module to see what Garmin says to radio. I see that PUTTY gives strange strings - without sense just garbages. It not seems to be NMEA but I mentioned above it works with VHF. Where is the problem? I use OpenCpn on Windows 11

[continuouswave]

Originally Posted by adam.lazarski

Laptop sends sentences $IPRMC and $IPGLL which are accepted by radio (according to VHF manual).

The portion of the sentence "$IP" is the TALKER ID.

The portion of the sentence "GLL" or "RMC" is the sentence identifier.

For an ICOM M422 radio, the manual states that the radio accepts the sentence GLL or RMC, but the manual no where mentions anything about a TALKER ID of $IP (or a any other TALKER ID value).

The radio is probably expecting the TALKER ID to be $GP.

In a very comprehensive investigation into the NMEA-0183 protocol, the known TALKER ID's are provided, and there is no mention of a $IP. Compare at

https://gpsd.gitlab.io/gpsd/NMEA.html

I suspect that the cause for the ICOM M422 radio to NOT accept position data in a sentence GLL or RMM is due to the TALKER ID being something totally unexpected by the radio.

My experience is that unusual TALKER ID use in communication to a VHF Marine Band radio of position data results in a problem. For more about this see

TALKER ID
https://continuouswave.com/forum/vie...hp?t=834#p6079

Because the NMEA organization refuses to provide open and unencumbered information about the details of their NMEA protocols and requires confidentiality and non-disclosure from all who have purchased their reference documents, almost everything known about NMEA-0183 is from observations and deductions or from disclosures by manufacturers of equipment using NMEA protocols.

CHECKSUM
Another possible cause of error in the communication between a source of position data and the radio may be the CHECKSUM. The radio may be STRICT about testing a received NMEA-0183 sentence for compliance with the CHECKSUM error check. If the transmitted sentence omits the CHECKSUM or has an incorrect CHECKSUM, the radio may ignore the sentence.

Conforming to strict checking of a packet's CHECKSUM seems to be optional for some devices.

[PippaB]

Originally Posted by adam.lazarski

.... I see that PUTTY gives strange strings - without sense just garbages. It not seems to be NMEA but I mentioned above it works with VHF. Where is the problem? I use OpenCpn on Windows 11

Since you say other data flows appear to work this would make me think the baud rate on the laptop is not correct. The baud rate on a PC usually defaults to 9600, NMEA 0183 standard is 4800, or with AIS 38400. Traffic with garbage in serial is frequently mismatched baud (or, less common, mismatched bit/parity settings).

[continuouswave]

Originally Posted by adam.lazarski

I connected Garmin to laptop by UART module to see what Garmin says to radio. I see that PUTTY gives strange strings...

Check that the baud rate in use is set to the same value for both the TALKER port on the sending device and the LISTENER port of the receiving device.

The default NMEA-0183 baud rate is 4800 baud. There is an option for a High Speed port to use 38,400 baud. If there is a mismatch, the communication link will fail or produce erroneous output.

A mismatch in port speeds would explain the behavior you reported.

[Moontide]

Third vote for a baud mismatch.

[smac999]

Why would you want to rely on having your laptop on to have pos on the vhf? I would install a dedicated nmea 183 antenna for it.

[CarinaPDX]

NMEA 0183 is based on the RS-422 spec, NOT RS-232. Much of the time the ICs used as terminals can inter-operate, but not always. So first thing to do is to is use a USB to RS-422 adapter, not an RS-232 adapter.

NMEA 0183 is defined to operate at 4800 baud. High Speed 0183 (NMEA 0183-HS) is defined to operate at 38.4kbps. Some compatible gear support other rates but they are non-standard. Of course the best way to find out which your equipment uses is to RTFM - it is (almost) always documented. But for marine gear from marine suppliers the best bet is 4800 baud.

I suspect that the talker ID is not the problem, as long as it is formatted correctly. The radio is looking for the sentence type and probably ignores the talker ID - but anything is possible.

Good luck.

Greg

[team karst]

I thought 0183 was close to RS423. Unipolar, 5v ish. Apple try back in 1990 or so.

[Squanderbucks]

You have a Garmin win 0183 In and Out at "normal" and High Speed. They try and KISS and forego any talk of BAUD rates. High Speed fro AIS and Normal for everything else.
Why not just use the 0183 out from it to the Radio - that is what I do with mine just for DSC. The chartplotter feeds both the radio and a PC with OpenCPN. I have a 0183 bar setup for sharing the data to anything that needs 0183 leftover from before I went mostly now to NMEA 2000.

That way all the Lat/Lon stuff is hard wired and the WIFI just for fun stuff like tablets and phones.

[CarinaPDX]

Apple's LocalTalk networking was RS-422 also. RS-422 uses a maximum of -6V to +6V differential voltage. RS-232 uses +3V to +15V for 0, and -3V to -15V for 1, relative to ground. They are quite different...

Greg

[team karst]

https://en.m.wikipedia.org/wiki/RS-423

An orphan. Signal voltages like 422, but unbalanced wiring like 232.

[adam.lazarski]

I tried to change baudrate from 2400 to 38400, changing parity, checksum etc. Garmin works ob 4800. So maybe I have to use other adapter such rs422…