On Wed, 22 Oct 2003 13:22:48 GMT, (Larry W4CSC)
tempted fate with:



In the past, NMEA listeners had quite a relatively low input
resistance that loaded the circuitry, rapidly, to peak current
capacity. But, if you put your ohmmeter to the input of the new
devices, you'll find they act almost like an open circuit.

In our "No Computer" configuration on Lionheart, the RS-232 TX output
from the Noland Multiplexer is applied to the master data output
circuit that feeds all the listeners. Noland warned me it was only
capable of 15ma of current, unlike the TLK NMEA outputs which will
sink a lot more. They told me overloading or shorting wouldn't hurt
the Noland multiplexer, it would simply not have sufficient output
levels to key the listeners.

The listeners connected to the master data output a
Icom M602 VHF xcvr
Icom M802 HF-SSB xcvr
Raymarine RL70CRC radar/chartplotter
Garmin 185 GPS/Sonar
B&G Network Pilot autopilot
B&G Yeoman paper chart drafting table
and, at times, a Dell Latitude P4 notebook computer's serial port when
someone forgets to flip the switch to COMPUTER ON.

With all these loads, the 15ma output limit of the Noland multiplexer
runs them all just fine with valid data. Nothing seems unstable.....


Interesting. I'd have bet money that would be a flakey setup. You
learn something every day (well you do if you're paying attention.)
If I felt sure that my customers had someone of your expertise aboard,
I might even be comfortable recommending something like that. :-)


__________________________________________________ __________
Glen "Wiley" Wilson usenet1 SPAMNIX at worldwidewiley dot com
To reply, lose the capitals and do the obvious.

Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at http://www.worldwidewiley.com/

On Wed, 22 Oct 2003 14:26:43 GMT, "Glen Wiley Wilson"
wrote:

Interesting. I'd have bet money that would be a flakey setup. You
learn something every day (well you do if you're paying attention.)
If I felt sure that my customers had someone of your expertise aboard,
I might even be comfortable recommending something like that. :-)

What ****es me off is the manufacturers rarely use a BALANCED feed,
i.e. NMEA + and NMEA - like it calls for. Much cheaper to unbalance
it. The stupid Icom M802 HF-SSB NMEA data input is a GROUNDED BNC RF
connector! That's crazy! Nothing like feeding SSB RF straight from
the radio's cabinet into NMEA - to cause havoc. Of course, if you
hook the coax shield of their connector to SCREEN, instead of NMEA -,
there's no data input to the Icom.....dammit. Idiots.

Garmin has + wire and ground
B&G Network output + wire and ground
Yeoman in and out + wire and ground
Icom M602 VHF in and out + wire and ground

Plenty of room for lots of RF intrusion into the NMEA system and it
all radiates like hell into the HF and VHF from all the stupid
unshielded screw terminals, push terminals, plain wires, unshielded
SeaTalk connectors/wires, it all drives the HF-SSB bands crazy jamming
the receiver with its stupid data noises. The boxes aren't shielded,
either. Garmin's plastic case, Raymarines are all in plastic cases,
B&G's are all in plastic, except for the main computer on the Network
Pilot. The data computer inside the display of Pilot is all plastic
you can see through...unshielded, of course.

Noone seems to care if the data instruments radiate into the radios or
are scrambled by the radios as long as profits are maximized. No
organization forces them to conform to any computer ratings like your
home computer.

It's all nuts.......damned NMEA is gutless to change it.



Larry W4CSC

3600 planes with transponders are burning 8-10 million
gallons of kerosene per hour over the USA. R-12 car air
conditioners are responsible for the ozone hole, right?