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Re: NMEA - Not More Electronics Agony!
Steve, it is possible for new equipment to be DOA.
So my first thought would be to test the new equipment, connect it to *one* "known good" NMEA talker and see if you can get it to listen, then vice versa.
Similarly, try connecting the old equipment (or at least, one piece at a time) to something simpe and dumb like an old Palm PDA, or a computer serial port, and see if the old equipment is actually putting OUT NMEA.
Sometimes the problem is simply that "RX/IN" and "TX/OUT" have been swapped, often due to bad diagrams or from too many pieces of equipment not making it clear that "IN" and "OUT" are just different ends of the same cable.
IIRC if you connect a simple DC voltmeter on a 5-12V scale to an NMEA bus, you should see a pulse every time data is sent onto the bus. No pulses? There's no data. A GPS should send a pulse once per second, with the typical GPS output strings.