Keith, looks like you've got it licked! Like Meindert said....a hidden
ground loop. Pretty common....

You got off easy......sometimes these things are tough to track down.

fair winds......Joe
"Keith" wrote in message
...
It gets stranger. I did unhook each device from the expander one at a
time,
and nothing made any difference. Of course, turning the GPS off or
disconnecting the power to the NMEA expander made the noise stop. Now get
this: I was hooking up the power to the NMEA expander, and I connected
JUST
the positive lead, and it started transmitting the data, still with the
noise of course. NO ground hooked up at all to the "supply" side. One of
the
four devices hooked up is somehow supplying a ground of it's own.

The four items a
Raymarine Radar
Standard Horizon VHF
ICOM 802 SSB
Computer running Nobeltec VNS

????????????

Well, I finally took out the expander and hooked up a terminal strip with
the NMEA data coming in and hooked up to all four items NMEA IN wires, and
their four (-) wired jumped together, but not hooked to ship's ground at
the
terminal strip, and it works fine, drives all four items, and no noise any
longer.

Things that make you go HMmmmmmmmmmmm...

"JAD" wrote in message
...
Keith, you need to do some more snooping to try to isolate where the
"noise"
is coming from, and how the RFI is getting into the set! You are on
the
right track so far.......

FIRST, with the noise present on the SSB,. turn off ONE NEMA device at
the
time to try to see if one of them (above all others and, of course, the
expander) is THE culprit. Is the expander taking ship's DC from the
same
power bus as the SSB? Are they physically close if on the breaker
panel?

With the NEMA unplugged from the SSB, remove the antenna cable from the
back
of the SSB...is the noise still there? Would it be easy to power up the
SSB
with a separate power source away from ship's DC....another battery
perhaps....with it's power leads run clear of the NEMA devices?

Looks like you may have to add some ferrites to the various NEMA cables,
your power cables....or shield the device in question.

Take note of what makes the noise lessen or go away completely.

Post your answers here and the experts will take over.....

Good luck.....Joe


"Keith" wrote in message
...
I have a problem that's got me stumped. I am getting NMEA string noise
in
my
SSB on various channels, starting with 2162.

I have a Garmin GPS that feeds into a Noland Engineering NMEA
Expander.
The
SSB and three other devices come out. When I turn the power off to the
expander, I lose my GPS signal to all of the devices. When I power it
up,
I
get the noise in the SSB.

I even hooked the SSB NMEA cable to the input side of the expander,
directly
to the GPS signal, and I still get the noise when the expander is
turned
on.
Thinking the expander was bad, I contacted them, and they sent a new
one.
Same problem. I even get the noise in the SSB when the NMEA data cable
is
unplugged from it. It has to be coming in either radiated or through
the
power supply.

I'm lost... any suggestions?