On Wed, 22 Oct 2003 00:47:45 GMT, "Glen Wiley Wilson"
wrote:


7. To send the GPS signal both to the PC and and the radar, do you
want to split the signal before the PC, or forward the data to the
radar from the PC? Technically, you are supposed to be able to drive
up to 4 NMEA "listeners" from a single NMEA "talker" but I have never
actually done this. You can also buy an NMEA expander which is
designed to drive multiple NMEA circuits, but I think this would be
overkill. Some multiplexors have an NMEA talker port as well as a
serial port, which should work well for you. Don't forget to feed the
autopilot, though.

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.....



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?