Do you "network" NA to multiple computers?
Would you like to extend the "RS-232" line length limit?
Three years ago I was getting ready to operate with WB1GQR M/L (VHF test) off
Mt. Equinox here in Vermont. He had used NA for years, but had only
"networked" in his shack and for very small distances. Even with the short
runs, he would occasionally have problems with the KW getting into the
network. On top of Equinox, we were looking at 300+ feet between our
stations. Basically, we had to run around the perimeter of the parking lot.
Obviously, RS-232 wasn't going to cut it. Here's my solution that has
performed flawlessly for all these years.
I use a device on the serial port (we use a single serial port configuration
in a loop) called an "Async Line Driver". Sometimes these are referred to as
"Short Haul Modems". What these do, is convert the RS-232 unbalanced signal
to a balanced 4 wire connection. The devices I use derive their power from
the serial port, but can also be externally powered. They come with either a
DB-25 male or female for the RS-232 side, and come standard with two types of
connections for the interconnect side, screw terminals or a convenient RJ-11
connector (that's what I use). The spec on these devices allows RS-232 data
to extend 1.2 miles at 19,200bps. We run 2400bps, so 300 feet ain't much of a
problem, :-} In three years, I have yet to see these get clobbered by RF. On
Equinox, we not only had our setup, but Zack, W1VT was running everything
from DC to Light up there. Rovers also would should up.
Our loop configuration is set up just like the standard loop configuration in
the NA manual, except that we have TX+ and TX- and RX+ and RX- because of the
Balanced configuration. TX+ would go to RX+ and TX- would go to RX- on the
next machine etc.
For cabling, I have a 500' reel (Garden Hose Reel) of Belden Data Twist cable
(left over from a network job) that has multi-pin connectors at each end.
These plug into breakout boxes that we then use RJ-11 connectors to hook up
individual machines. The Belden cable has 4 pair or 8 wires. We only use four
(2 pair twisted) for the network, and use the other wires for signaling. I
show up at the Mountain and just pull the cable off the reel, connect the
breakout boxes and run the RJ-11 jumpers and go! 15 minutes! BTW, we run 4
computers continously. We use them for *everything* Logging, Passes, Gab
functions etc. I like the fact that I only need to concentrate on my computer
screen and radio. No Field Phone to pick up when it rings etc..... If someone
want to send me a message, it comes in via the network. (The Gab function
logs to disk. We have a great time after the test at our usual pizza orgy
re-reading the messages that flew back and forth on the network during the
test. It gets weird at 2A !!)
These devices are available from a variety of computer network suppliers.
Black Box (I don't have their number right handy)
Misco has one of the better prices right now in their Feb '97 catalogue. $50
(part # JJ2646 for the DB-25 female) I know this isn't real cheap,
especially if you're looking at a lot of machines, but it certainly
simplifies network runs. It leaves us time to figure out why the 70cm preamp
died again or check that KW amp one more time. Bottom Line, one less thing to
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