On Apr 10, 6:10 pm, "Roger Long" wrote:
Goofball_star_dot_etal wrote:

it is odd. Is your radio model here?
http://www.standardhorizon.com/?cmd=...s&DivisionID=3

Yes, it's this one:

http://www.standardhorizon.com/downl...323&FileCatID=...

I left the manual on the boat because I didn't start wondering until the
drive home.

Looking at the PDF version (thanks for the link), I see that the radio calls
both wires "NMEA IN", one is + and the other - so connecting to ground makes
sense. But, why wouldn't they just do that inside the radio and have you
just connect one wire?


Noise rejection. A balanced, or bifilar connection, is immune to
external signal interference, same like for low impedance microphone
lines. The (-) connection is not a ground.

Terry K