0183 needs to be the correct level particularly if you are splitting it to multiple places. If you have more than two listeners, you might also need something that will amplify so there isn't too much load on the device. There are many off the shelf RS232 to RS422 converters and I can't say I have tested them all or have a preference. Given a preference, I likely wouldn't be using the ONWA sensor as version 2 NMEA which it puts our can't be NMEA certified as v2 is when NMEA started requiring RS422 to obtain certification. Sometimes cheap is just that and when at sea it not the time to have difficulties.