"Larry" wrote in message
...
Interesting information on:
http://www.interfacebus.com/NMEA-2000_Standard.html

"CAN Bus uses a Drive Voltage: High; 2.75v to 4.5volts, Low; 0.5 to
2.25volts, Differential 1.5v to 3.0volts"

and...once again....we're stuck with an interface bus whos lack of good +
and - voltage levels dooms us to slowdowns from cable length, system
noises, intersecting fields....just like an old unbalanced mic.

Larry, you're talking nonsense now. It is a *balanced* bus and therefore
insensitive to noise,.just like your favourite ethernet, and the voltage
levels are even *higher* that your favourite ethernet. So don't whine if you
don't know what you're talking about.....

Someone emailed me to ask what I thought this would do for his HF noise
problem, where his NMEA0183 system trashes his M802/AT130 across the HF
spectrum, rendering it useless unless you shut down the whole NMEA network
if you want to use HF or NAVTEX or WEFAX or Sailmail or ham radio.

If his NMEA-0183 network trashes his HF comms, there is something wrong with
the installation. Example: we tested our multiplexers for RFI and the
emissions where below the limits of the IEC/EN60945, which means you cannot
hear any interference on marine HF and VHF bands. This simply means that
NMEA-0183 can be perfectly HF friendly. One mistake made by many people is
that they connect a balanced/differential output to a single ended input,
effectively connecting the B signal of the output to ground. That *will*
produce HF interference but this is simpy caused by wrong wiring.

CANbus is used in every new car, which is where NMEA ripped the idea in
the
first place. I'd like to invite you all to beg, borrow or steal a
portable
shortwave receiver (HF) and go for a ride in a 2000+ car/truck or SUV up
the interstate. Listen up and down the HF spectrum to see what CANbus
sounds like coming from the car's network system. HF ham radio is damned
near useless in a new car or truck.

CAN in cars is often single ended and therefore radiating as hell. CAN in
NMEA 2000 is balanced and should be silent. Especially when NMEA-2000
equipment is EN60945 certified (mandatory when used on vessels sailing under
SOLAS rules), you can be absolutely sure that it does not interfere on
HF/VHF.

It's just awful..... Will boats be
different? Looking at Lowrances cheap plastic connectors, you just know
the system will be all balanced and all just sealed up tight with
shielding, included shielded instruments, right? Yeah, right.....

Even plastic connectors can have shielding Larry. Besides, does you
favourite ethernet network produce any interference on HF (being UTP and
all, plastic RJ-45 etc. etc.)?

Meindert