When I turn on my SSB radio, I hear what appears to be the NMEA
sentence being transmitted. It sounds kind of like morse code.
Disappears when I turn the GPS off. The GPS signal is being fed into
the SSB, the VHF, the navigation computer and the radar. This noise
doesn't appear anywhere else... any ideas?

"Keith" wrote in message
oups.com...
When I turn on my SSB radio, I hear what appears to be the NMEA
sentence being transmitted. It sounds kind of like morse code.
Disappears when I turn the GPS off. The GPS signal is being fed into
the SSB, the VHF, the navigation computer and the radar. This noise
doesn't appear anywhere else... any ideas?

Is the signal fed into the SSB, VHF, computer and radar directly from the
GPS or did you use a buffer/splitter?

If so, read a bit about single-ended and differential NMEA connections at
http://www.shipmodul.com/en/index.html

There is a good chance that a differential output of a splitter is connected
to a singe ended input (an input with ground). What happens then is that one
signal of the output is short-circuited to ground, resulting in high
currents, in turn producing harmonics up to the HF range.

Meindert

"Larry" wrote in message
...
"Keith" wrote in
news:1148989790.905246.127580
@u72g2000cwu.googlegroups.com:

any ideas?


Welcome to NMEA, the big interference transmitter aboard!

Nonsense. It's the sometimes crappy implementations that do the harm.

I've given up
trying to cure it. Damned unbalanced connections, grounding the - NMEA
terminal causes a lot of it. Stupid NMEA, itself, trying to save the
manufacturers a few bucks with no shielding, no shielded connectors, screw
terminals all over in plastic boxes....we did it to ourselves. How
stupid.

Again, nonsense. Example: our multiplexers are tested and being certified
for IEC 945/EN60945 which imposes very low limits of allowed radiated RF.
The tests are done with cables attached to the multiplexer, transmitting
data over the cables. These cables are not shielded and the emissions stay
below the legal limits, which means you can hardly hear them above the noise
floor on HF and VHF.

Best of luck trying to cure it. None of the plastic boxed computers
running all over the boat on the network are properly shielded, either,
making the problems even more acute. They all radiate like hell to the HF
antenna.

Again nonsense. The very same multiplexers are housed in plastic. It just
comes down to proper filtering on all terminals and a decent EMC-proof
printed circuit design.

I just turn it all off when I'm on HF. The big transmitter scrambles the
data, anyways radiating into all the unbalanced, unshielded crapware.

Oh and the same rules apply the other way around. They have to withstand a
fieldstrength of10V/m, 1kV induced spikes on the terminals, contact
discharge of 6kV on the terminals and 8kV near the housing. All tests
passed. What's that again about stupid NMEA?

NMEA is nothing more than a RS-422 connection, something that is used all
over the world without problems. It's just that some manufacturers screw up
big time...

Meindert

"Meindert Sprang" wrote in
:

NMEA is nothing more than a RS-422 connection, something that is used
all over the world without problems. It's just that some manufacturers
screw up big time...


Not at all. No RS-422 connection is made with screw terminal from little
bare wires sticking out of a plastic plug, plugged into a plastic box.

There have never been any screw terminals on any of my computers....er, ah,
well, since the first one back in the early 70's...(c;

All those manufacturers you refer to are the trouble, the cheap *******s.
$500 and it comes with wires sticking out of it, 30 cm long.

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

NMEA is nothing more than a RS-422 connection, something that is used
all over the world without problems. It's just that some manufacturers
screw up big time...


Not at all. No RS-422 connection is made with screw terminal from little
bare wires sticking out of a plastic plug, plugged into a plastic box.

Oh? When I look for RS422 converters on Google, several boxes turn up that
all have screw terminals for the RS422/485 connection.

Look at Moxa, a brand that is used a lot in industrial applications:
http://www.moxa.com/product/Media_Converters.htm
Plastic box, screw terminals.

There have never been any screw terminals on any of my computers....er,
ah,
well, since the first one back in the early 70's...(c;

I think you'll find more RS-422 devices with screw terminals than with
connectors. Talk to a professional installer why this is.

Meindert

The cable comes from the GPS to a terminal strip, then from there to
the various instruments. I used a Noland Multiplexer once, but it
didn't seem to make any difference and actually seemed to harm the
signal, so I took it out.
I'll go check out the article you mentioned, thanks.
Meindert Sprang wrote:


Is the signal fed into the SSB, VHF, computer and radar directly from the
GPS or did you use a buffer/splitter?

"Meindert Sprang" wrote in
:

I think you'll find more RS-422 devices with screw terminals than with
connectors. Talk to a professional installer why this is.

Meindert



I give up. The problem here is RF interference with very close by HF radio
equipment used on BOATS. No amount of excuses is going to change the fact
that the damned screw terminals, unshielded wiring (even balanced, which
it's not) and open cabling hooked to the big boat DC antenna is going to
change it.

NMEA should have used a SEALED, WATERPROOF, SHIELDED connector, STANDARD to
all devices from all manufacturers to eliminate RF interference. They
should have mandated the inside of the cheap plastic boxes be painted with
shielding paint and displays be covered with shielding plastic to stop the
radiation from there. They didn't. Everyone "did their own thing", like
you did. The customers pay for it with all this non-standardized ****ware
screwed together with the corroded wiring and rotting terminal strips open
to the sea air.

Stupid...really stupid.

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

I think you'll find more RS-422 devices with screw terminals than with
connectors. Talk to a professional installer why this is.

Meindert



I give up. The problem here is RF interference with very close by HF
radio
equipment used on BOATS. No amount of excuses is going to change the fact
that the damned screw terminals, unshielded wiring (even balanced, which
it's not) and open cabling hooked to the big boat DC antenna is going to
change it.

The issue is: when a device is designed properly, there is nothing to
transmit. Even IF you use unshielded cable and screw terminals. The output
signal of a 4800 baud port should be frequency limited with an internal
filter to prevent fast transients on the signal. If that is done properly,
there is nothing to transmit on whatever cable used.

NMEA should have used a SEALED, WATERPROOF, SHIELDED connector, STANDARD
to
all devices from all manufacturers to eliminate RF interference.

Again, not necessary.

They
should have mandated the inside of the cheap plastic boxes be painted with
shielding paint and displays be covered with shielding plastic to stop the
radiation from there.

Why? if the design is right, no need for shielded housing.

They didn't. Everyone "did their own thing", like
you did. The customers pay for it with all this non-standardized ****ware
screwed together with the corroded wiring and rotting terminal strips open
to the sea air.

Using nickel plated brass/copper terminal strips prevents corrosion, indeed
like I did. The drawback of connectors is that 1) you have to mount them,
which is something not everyone can do properly and
2) when moulded to a cable, you have to drill oversized holes to run the
connectors through. That's why most installers like bare cables and screw
terminals. At least, that's what they tell me.

Your everlasting rant against this holds no ground.

Meindert

There have never been any screw terminals on any of my computers....er,
ah,
well, since the first one back in the early 70's...(c;

Bull, but then it's clear you've never seen or worked with industrial or
military computers. They continue to have screw terminals for all sorts of
connections. Mostly to guarantee secure connections.

All those manufacturers you refer to are the trouble, the cheap *******s.
$500 and it comes with wires sticking out of it, 30 cm long.

Indeed, but that's always been the case.

Good, fast, cheap... pick two.

I give up.

We can only but pray...

NMEA should have used a SEALED, WATERPROOF, SHIELDED connector, STANDARD
to
all devices from all manufacturers to eliminate RF interference.

Which NMEA 2000 offers.

Stupid...really stupid.

And meanwhile a great many improvements came along, utilizing the NMEA-0183
standard. Things evolve, and those that recognize change has costs have
benefitted greatly along the way. Sure, plenty of vendors have done a
less-than-ideal job of implementing it, but that's true for everything.
Meanwhile we've evolved away from purely proprietary cruft, that alone makes
it worth the hassles.