GeoffSchultz wrote:
At my nav station I have a bus bar with jumpers...snip

Connecting multiple equipments to a single RS-232 output can drop or
overload the signal levels and affect the quality and performance some
or all of the connections. I think that can generally start happening
with more than two or maybe three three devices connected. That might
be the root cause of your problem here.

In a more professional installation, a signal multiplexer would normally
be used for what you are doing. Using one of those will usually add
some more features too, like allowing more than one talker to share NMEA
data with multiple listeners. And some will allow data exchange with
proprietary flavors of RS-232 (like Raymarine's SeaTalk) and have
Bluetooth and other more modern whizzbang features.

If you are crafty, you can make your own:

http://www.vimms.org/multiplex/docu.html

Or you can buy one of the good ones intended for marine use:

http://www.shipmodul.com/en/index.html

http://www.nolandengineering.com/

http://brookhouseonline.com/nmeamux_ext.htm

Jack

--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)