Does this sound right? - NEMA question
 

I hooked up the NEMA output from my Garmin GPSmap 76x to my Quest radio this
morning.

The radio has a NEMA in and NEMA out line and shows them connected to wires
of the same color for a GPS by the same company. A few pages later there is
a table for NEMA connetions to various brands of GPS.

Both fixed mount and portable Garmin's show the NEMA out line from the GPS
to be connected to the :Data In" in line on the radio. The radio "Data Out"
line is indicated as connecting to "Black - Neg Ground". I therefore put a
wire from the ground block where the black negative lead from the GPS power
cord attaches and ran it to the Quest radio "Data Out" lead. I'm sure this
is what it said to do but it seems odd.

I haven't turned anything on yet so, if anyone can confirm that I did it
right or head off melting something, I would appreciate it.

Please: only if you know. I hate those post responses that start out, "I
haven't got a clue but here is what I guess."

--
Roger Long

Does this sound right? - NEMA question
 

On Tue, 10 Apr 2007 14:20:42 -0400, Charlie Morgan
wrote:

On Tue, 10 Apr 2007 14:16:15 -0400, "Roger Long"
wrote:

I hooked up the NEMA output from my Garmin GPSmap 76x to my Quest radio this
morning.

The radio has a NEMA in and NEMA out line and shows them connected to wires
of the same color for a GPS by the same company. A few pages later there is
a table for NEMA connetions to various brands of GPS.

Both fixed mount and portable Garmin's show the NEMA out line from the GPS
to be connected to the :Data In" in line on the radio. The radio "Data Out"
line is indicated as connecting to "Black - Neg Ground". I therefore put a
wire from the ground block where the black negative lead from the GPS power
cord attaches and ran it to the Quest radio "Data Out" lead. I'm sure this
is what it said to do but it seems odd.


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




I haven't turned anything on yet so, if anyone can confirm that I did it
right or head off melting something, I would appreciate it.

Please: only if you know. I hate those post responses that start out, "I
haven't got a clue but here is what I guess."

I haven't a clue, but your Garmin won't output NEMA until you tell it
to in the setup menu. It defaults to Garmin's proprietary language.

CWM

Does this sound right? - NEMA question
 

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?

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.

--
Roger Long

Does this sound right? - NEMA question
 

Charlie Morgan wrote:

I haven't a clue, but your Garmin won't output NEMA until you tell it
to in the setup menu. It defaults to Garmin's proprietary language.

Yes, the GPS manual covers that pretty clearly but my question was about
something else.

--
Roger Long

Does this sound right? - NEMA question
 

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.

Does this sound right? - NEMA question
 

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?

Officially, an NMEA-0183 input should be optically isolated, so your
two leads are the anode and cathode of an LED in an optocoupler.

Also officially, an NMEA output should be differential - there should
be a +out and -out which would connect to the +in and -in. However
most manufacturers seem to economize, and use a single-ended output,
and many also use a single-ended (non-isolated) input.


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.

Not having an internal ground makes the input a "proper" NMEA input.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

Does this sound right? - NEMA question
 

"Roger Long" wrote in
:

Both fixed mount and portable Garmin's show the NEMA out line from the
GPS to be connected to the :Data In" in line on the radio. The radio
"Data Out" line is indicated as connecting to "Black - Neg Ground". I
therefore put a wire from the ground block where the black negative
lead from the GPS power cord attaches and ran it to the Quest radio
"Data Out" lead. I'm sure this is what it said to do but it seems
odd.



Don't ground the data lines, no matter what it says. No sense having the
Quest output IC operating into a short, which might shorten its life.
It's a happy camper operating into an open its whole life. Just insulate
the open output lead with tape. Data out of the GPS hooks to Data in on
the radio. That's all it takes.

Be informed that only ONE "talker", a device that SENDS data out on the
archaic NMEA serial bus is allowed. Up to 16 "Listeners", devices that
listen to the ONE talker, is allowed before the talker's output gets
loaded so bad the data received starts faulting. If you have more than
ONE talker on your NMEA network, you must contact Meindert at Shipmodul
to order his "multiplexer" (DID I DO IT RIGHT, Meindert??..(c;). A
multiplexer has, usually, 4 input lines to hook the talkers' data outputs
to, one talker per input port only please. The multiplexer stores all
the data pouring into it in internal memory, simultaneously, from the
uncontrollable talkers, then, "services" each input port, in sequence,
reading and clearing each ports memory as it dumps what it finds into the
OUTPUT terminals of the multiplexer for all the listeners to hear, in
sequence instead of all crashed at once together. This round-robin
sequencing continues, ad nauseum, as long as the system is on. Some
multiplexers route data from the input ports through the RS-232 serial
ports to your nav software, so the computer can digest and massage the
data before it comes back out of the computer to be digested by the NMEA
listener devices. This is how the nav software, for instance, adds
waypoint data to the NMEA serial data stream the listeners get. The
computer stalls the data the multiplexer is feeding it, then injects its
data, then resumes the data stream from the multiplexer, transparently to
the listeners.

NMEA is simply a proprietary-data on an RS-422 serial bus (switches from
0=0V to 1=+5V back and forth). Older computer had RS-232C serial ports
that some could read 5V data, but RS-232C has 0=-12V and 1=+12V making it
more immune to noise that gets into the data lines, making NMEA's mostly-
ignored + and - balanced wire scheme unnecessary. NMEA chose RS-422
because they'd had to have -12V power supplies in all their +12V stuff if
they chose RS-232C. It's all moot, now, of course. The whole damned
world has gone Ethernet or USB data which is much more intellegent....

Larry
--

Does this sound right? - NEMA question
 

"Roger Long" wrote in
:

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?



Well, yes and no. Connecting NMEA - to ground is because the cheapassed
NMEA manufacturers departed from the balanced, noise-free lines the
original RS-422 specifications had to save a few pennies/unit. Most NMEA
outputs only have one wire and ground....ground is NMEA - as soon as one
listener or the talker grounds NMEA - at only one point....making all that
data noise in the damned RADIOS! Grounding NMEA - doesn't hurt anything as
long as you don't also have NMEA + GROUNDED at any point in the system. In
your post, I thought you were grounding both NMEA - AND + to ground.

Garmin only uses NMEA + for data....damn them. So doesn't Icom...damn
them, too.

Larry
--

Does this sound right? - NEMA question
 

"Charlie Morgan" wrote

Just thought I'd mention it as this minor issue has tripped up many folks
before
you. They get everyting wired correctly and it doesn't work. You'd be
amazed at
how often this has been the reason. Just trying to be helpful. Sorry for
the
intrusion.

No, I'm the one who should apologize. I lost sight of what I often try to
point out. These are not private conversations but are for the benifit if
other readers. What you pointed out could be very useful to another reader
and was right on topic.

--
Roger Long

Does this sound right? - NEMA question
 

Thanks Larry, you are a treasure.

I think I have it straight now although I had to look carefully at the
timing of your posts since the second appeared higher in the list.

No network here. My set up is about one baby step past a pencil and a
parallel rule. The handheld GPS is wired directly to the fuse for the
depth sounder and knotlog. The GPS "Data Out" line goes directly to the
radio "Data +". The radio "Data -" goes to the ground block on the same
screw that GPS power - connects to. The radio is on a separate fuse.

It sounds like I can expect to hear the GPS talking to the radio in the
background. Would it be a good idea to put a switch in the data line near
the radio so I can silence it in conditions where I am having trouble
hearing or understanding or just don't like the noise? I would probably
leave it off most of the time as I'm only wiring this up for the cool factor
and so I will have my position handy if I ever need to call for help and
don't want to have bring the GPS in from the steering station.

The radio data lines go to a two screw terminal block. When I purchase a
back up GPS, I will probably dedicate that one to talking to the radio so I
still have position data available if the one in the cockpit mount goes
overboard.

BTW I have a ferrite core on the GPS lead. When I install the autopilot,
I'm going to avoid tying the power supply to in in the same convienient
cable run as the GPS and lead it separately with its own ferrite core.

Another question that just popped into my mind:

When flying, we were religious about making sure that all power to the
radios and instruments was turned off before starting or stopping the
engine. I use my two battery bank as a single battery (for reasons
discussed at length a couple years ago). Am I at risk of frying or
shortening the life of my simple electronic items? I've gotten away with it
for two years as have apparently many other people. Saiing involves
frequent engine starts and shut downs while navigation is in progress so a
voltage suppressor in the power supply to the instruments would be a better
solution than an avionics master switch such as I had on the aircraft.

--
Roger Long