Connecting Icom M502 to serial GPS unit
 

Hello all,

A week ago I bought myself an Icom M502. I already have an external
GPS unit which has a standard serial 9 pins connector.
Does anybody know which serial pins I use to connect to the NMEA in on
the Icom?

Thanks,
Ronald.

"RvdP" wrote in message
oups.com...
Hello all,

A week ago I bought myself an Icom M502. I already have an external
GPS unit which has a standard serial 9 pins connector.
Does anybody know which serial pins I use to connect to the NMEA in on
the Icom?

Pins 2 (TxD) and 5 (Com/Gnd).

Meindert

You need to get the wiring information for your GPS, probably on the
manufacturer's web-site, to identify which pins are for NMEA + and - wires.
If it's not in your GPS instruction book or the web-site, call or email the
manufacturer to get it.
I bought a serial connector to connect to the serial connector of my Garmin
and ran two wires from the + and - pins to my iCom (and my Furuno 1622 radar
display). Make sure you set your GPS interface for NMEA 0183, version 2. I
also set the GPS transmission speed for the slowest BAUD rate: the radar
doesn't display the GPS info if I set the BAUD rate fast.
Page 35 of the iCom 502 Manual
http://www.icomamerica.com/support/manuals/ic-m502.pdf
GPS RECEIVER JACK Connects to an optional GPS receiver to input the position
data and time data.

..A GPS receiver appropriate for the IC-M502 is not supplied from Icom. An
NMEA0183 ver. 2.0 is required for position or time indication, etc. Ask your
dealer about the GPS receiver.

NMEA (+) to center of RCA connector; NMEA (-) to edge of RCA connector



"RvdP" wrote in message
oups.com...

Hello all,

A week ago I bought myself an Icom M502. I already have an external
GPS unit which has a standard serial 9 pins connector.
Does anybody know which serial pins I use to connect to the NMEA in on
the Icom?

Thanks,
Ronald.

Bedankt..

Ronald. (eMVP)

"William Andersen" wrote in
news:w3fve.406$HV1.345@fed1read07:

NMEA (+) to center of RCA connector; NMEA (-) to edge of RCA connector


Ah, yet another damned unbalanced connection to ground to insure any
transmitter keyed will trash all the data in the NMEA bus throughout the
boat....(sigh)

Maybe they should make the whole damned NMEA system COAX THAT'S SHIELDED!!

--
Larry

You know you've had a rough night when you wake up and you're outlined in
chalk.

Larry, you bring up and interesting question that I am pondering. I am
going to be hooking my Garmin 176 up to my Simrad autopilot. The Simrad
nicely isolates the Nmea common from battery neg. Unfortunately, the Garmin
only has 4 connections, 12v+, Nmea in, Nmea out and common shared between
the Nmea and 12v -. If I connect this up, I'll be crossing the ships neg.
bus with Nmea common. This does not seem like a good idea to me. Do I need
to (or should I) be looking into some sort of optoisolator?

"Larry W4CSC" wrote in message
...
"William Andersen" wrote in
news:w3fve.406$HV1.345@fed1read07:

NMEA (+) to center of RCA connector; NMEA (-) to edge of RCA connector


Ah, yet another damned unbalanced connection to ground to insure any
transmitter keyed will trash all the data in the NMEA bus throughout the
boat....(sigh)

Maybe they should make the whole damned NMEA system COAX THAT'S SHIELDED!!

--
Larry

You know you've had a rough night when you wake up and you're outlined in
chalk.

"Johnhh" wrote in message
...
Larry, you bring up and interesting question that I am pondering. I am
going to be hooking my Garmin 176 up to my Simrad autopilot. The Simrad
nicely isolates the Nmea common from battery neg. Unfortunately, the
Garmin
only has 4 connections, 12v+, Nmea in, Nmea out and common shared between
the Nmea and 12v -. If I connect this up, I'll be crossing the ships neg.
bus with Nmea common. This does not seem like a good idea to me. Do I
need
to (or should I) be looking into some sort of optoisolator?

No.

NMEA is laid out to prevent ground loops in the datalines. This is achieved
by having every input isolated. The outputs need not to be isolated. And if
everyone adhered to that spec, there would not be any problem.
In your case, youll be fine since that situation is almost exactly to the
NMEA spec.

Meindert

"Meindert Sprang" wrote in
:

No.

NMEA is laid out to prevent ground loops in the datalines. This is
achieved by having every input isolated. The outputs need not to be
isolated. And if everyone adhered to that spec, there would not be any
problem. In your case, youll be fine since that situation is almost
exactly to the NMEA spec.

Meindert

But, alas, he's hooking one side of his NMEA dataline to GROUND! It's not
isolated at all at that point. The whole databus is now negative ground,
not balanced pair. Any intersecting signal...HF from the SSB...AC hum from
the inverter or genset...VHF or any other transmitter signal...has a ground
reference, or several references if more than one listener or talker has
unbalanced output like Garmin. Instead of intersecting signals being
balanced out, phoneline style, now we have a great UNSHIELDED antenna to
ground.

Foil shielded cables help, but every time you come to an NMEA instrument
the damned fools have cheap open wires you're forced to connect your
shielded cabling to...making a big point of intrusion, anyway.



--
Larry

You know you've had a rough night when you wake up and you're outlined in
chalk.

"Larry W4CSC" wrote in message
...
"Meindert Sprang" wrote in
:

No.

NMEA is laid out to prevent ground loops in the datalines. This is
achieved by having every input isolated. The outputs need not to be
isolated. And if everyone adhered to that spec, there would not be any
problem. In your case, youll be fine since that situation is almost
exactly to the NMEA spec.

Meindert

But, alas, he's hooking one side of his NMEA dataline to GROUND! It's not
isolated at all at that point.

If the output had been differential, there would have been a path to ground
as well though the internal impedance of the driver an output filters. This
situation makes no difference since the other end at the autopilot is
completely isolated. So any induced HF on both the data line and the ground
line are in phase and therefore generate no differenctial voltage at the
isolated autopilot end.

Read a textbook on transmission lines if you don't believe me.

Meindert

Oh boy, on a scale of one (none) to ten (good), my understanding is proably
about a 3, so bear with me. To complicate it further, I have lots of other
Nmea devices to hook up berfore I'm through. Radar, computer, DSC radio,
second or alternate GPS, but we don't need to get into that.

When I hook up the one GPS, both the NMEA in and out are going to be
grounded at or near the GPS. If I understand correctly, you are saying that
that is ok provided that it is only grounded at one point, correct?

Now, if I run shielded signal wire, where should the shield be grounded, or
does it matter?

Thanks
John


"Meindert Sprang" wrote in message
...
"Larry W4CSC" wrote in message
...
"Meindert Sprang" wrote in
:

No.

NMEA is laid out to prevent ground loops in the datalines. This is
achieved by having every input isolated. The outputs need not to be
isolated. And if everyone adhered to that spec, there would not be any
problem. In your case, youll be fine since that situation is almost
exactly to the NMEA spec.

Meindert

But, alas, he's hooking one side of his NMEA dataline to GROUND! It's
not
isolated at all at that point.

If the output had been differential, there would have been a path to
ground
as well though the internal impedance of the driver an output filters.
This
situation makes no difference since the other end at the autopilot is
completely isolated. So any induced HF on both the data line and the
ground
line are in phase and therefore generate no differenctial voltage at the
isolated autopilot end.

Read a textbook on transmission lines if you don't believe me.

Meindert