On Tue, 10 Apr 2007 17:10:04 -0400, "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...Name= GX1255S

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?

I forget the details of NMEA signals but basically it is a signal to
noise issue. It would be best to transmit balanced signals via twin
cable but it is cheaper to make it unbalanced, with one end or the
other, or both ends earthed.


Looking at the table, it looks like connecting to ground is the common for
many GPS types but not universal. Maybe not having a connection to ground
inside the radio is necessary for the other GPS types to work properly.