Connecting Icom M502 to serial GPS unit

Bedankt..

Ronald. (eMVP)
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

"William Andersen" <wgander.RemoveThis@cox.net> 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.
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

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" <noone DeleteThis @home.com> wrote in message
news:Xns9680E12C23F9Bw4csc@63.223.7.253...
> "William Andersen" <wgander DeleteThis @cox.net> 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.
>
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

"Johnhh" <john.RemoveThis@NS.harcharik.com> wrote in message
news:Vc-dndjmw8pLiSPfRVn-1Q@comcast.com...
> 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
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

Guys,

I do not know how far this thread is diverted from my original
question, but as soon as my M502 is here, I think in two days, I will
hook up the Serial Pin 2 to +NMEA and Serial Pin 5 to -NMEA (Per
Meindert) and I will let you know if the M502 is able to get a fix on
my location.

Ronald.
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

"Meindert Sprang" <mhsprang RemoveThis @NOcustomSPAMware.nl> wrote in
news:11bslg723abnt29@corp.supernews.com:

> 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.
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

So True..
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

"Larry W4CSC" <noone DeleteThis @home.com> wrote in message
news:Xns96816967E5839w4csc@63.223.7.253...
> "Meindert Sprang" <mhsprang DeleteThis @NOcustomSPAMware.nl> wrote in
> news:11bslg723abnt29@corp.supernews.com:
>
> > 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
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

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" <mhsprang.RemoveThis@NOcustomSPAMware.nl> wrote in message
news:11btk849tife62c@corp.supernews.com...
> "Larry W4CSC" <noone.RemoveThis@home.com> wrote in message
> news:Xns96816967E5839w4csc@63.223.7.253...
>> "Meindert Sprang" <mhsprang.RemoveThis@NOcustomSPAMware.nl> wrote in
>> news:11bslg723abnt29@corp.supernews.com:
>>
>> > 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
>
>
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

"RvdP" <ronald.vanderputten.RemoveThis@verizon.net> wrote in message
news:1119805818.988425.59000@g49g2000cwa.googlegroups.com...
> Guys,
>
> I do not know how far this thread is diverted from my original
> question, but as soon as my M502 is here, I think in two days, I will
> hook up the Serial Pin 2 to +NMEA and Serial Pin 5 to -NMEA (Per
> Meindert) and I will let you know if the M502 is able to get a fix on
> my location.

Good idea!

Meindert
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

"Johnhh" <john.TakeThisOut@NS.harcharik.com> wrote in message
news:A6adnSHyldUxRyPfRVn-3w@comcast.com...
> 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?

From the GPS to autopilot, this is ok. From another device to the GPS
theoretically it is not ok, but there is not much you can do about it. As
long as you keep signal and ground close together and possibly short runs of
cable, you'll be fine in most cases.

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

The common consensus is to ground the shield at the talker side, at the side
where the data is generated. Do not use the shield as signal- or ground
return but you can't anyway if you connect the shield only on one side.

Meindert
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

Thank you Meindert, I feel more comfortable with this now.

Ronald, sorry if I hijacked your thread. The mind is like a cruiser, it
wanders where it will.

John


"Meindert Sprang" <mhsprang RemoveThis @NOcustomSPAMware.nl> wrote in message
news:11btq1epg2ujk62@corp.supernews.com...
> "Johnhh" <john RemoveThis @NS.harcharik.com> wrote in message
> news:A6adnSHyldUxRyPfRVn-3w@comcast.com...
>> 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?
>
> From the GPS to autopilot, this is ok. From another device to the GPS
> theoretically it is not ok, but there is not much you can do about it. As
> long as you keep signal and ground close together and possibly short runs
> of
> cable, you'll be fine in most cases.
>
>> Now, if I run shielded signal wire, where should the shield be grounded,
> or
>> does it matter?
>
> The common consensus is to ground the shield at the talker side, at the
> side
> where the data is generated. Do not use the shield as signal- or ground
> return but you can't anyway if you connect the shield only on one side.
>
> Meindert
>
>
 >> Stay informed about: Connecting Icom M502 to serial GPS unit 

I've installed the M502 and the GPS unit. I created the GPS cable as
per Meindert.. (pin 2-5).

Works great!

Thanks..
 >> Stay informed about: Connecting Icom M502 to serial GPS unit