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Wireless 802.11 NMEA server
On Sat, 8 Nov 2003 09:09:57 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote: As a metal boat owner, I don't have a choice. The boat looks like a series of Faraday cages, with metal watertight doors pulled down against very thin gaskets and all the thru bulkhead fittings of minimum size. There will be no 3" gaps; one of the advantages of metal is that you have a good chance of keeping fire and flood in one compartment if you're careful. Sure wish I could get by your boat to test it out. Every wire going from compartment to compartment is a great antenna for 2400 Mhz....right through those watertight bulkheads. It would be interesting to see how far the usable signal got with the transmitter that close. Even if I had a choice, however, I'd probably stick with wire. A boat is not a house or office. Aside from alternators, we have a variety of sources of potential interference -- radios (150 watt sideband and 25 watt VHFs), radar, and so forth. 802.11 "should" ignore all of that. But "should" is a big word at sea. Although the 10baseT pairs could also act as antennas and could pick up RFI, my instinct is that it's a safer choice. The only 2400 Mhz RFI source on your boat is probably your microwave oven at 2450 Mhz. There is no interference from 150W of HF through the wireless.....LIKE THERE IS ON EVERY WIRE OF THE NMEA SYSTEM aboard the boat. NMEA wiring cannot be effectively shielded as long as manufacturers keep using hookup wire that's not shielded (Garmin) and even stupid Icom, itself, who made the M802 HF-SSB forces you to connect NMEA B (-) to the SHIELD OF A BNC CONNECTOR to hook NMEA input to the HF SSB with DSC. How stupid! Of course, NONE of the plastic boxes the damned cheap marine crap comes in is shielded in the first place against the HF transmitter or your 5W walkie talkie on deck. There's no FORCED standards, just NMEA suggestions from the NMEA the manufacturers control....sorta like the fox guarding the henhouse. As for using either the AC or DC lines, I have the same objection. And even in relatively small boats, the AC system is usually split bus (so you can plug in two 120V 30A lines to a dock), so you have to do some capacitive coupling. There's 2 primary transformers sitting on top of the floating dock at Ashley Marina. The powerline router signal coupled through them, to my amazement, good enough to get the WiFi through them. Of course in saying all of this, I do have the advantage that we're doing a major refit, and it's very easy to lay in an extra conduit for the network (actually it isn't even extra as we'll have a conduit for phone and signaling anyway). Certainly if I were adding a network to an existing boat that wasn't well set for easy access everywhere (that's another topic), I'd certainly take a shot at using wireless and test the hell out of it at the dock. On the larger boat, that's very nice. But, most boat manufacturers, in their attempts to maximize profits, don't put in even the most rudimentary conduit. The wires are just haphazardly laid in behind some panel squished between the panel and the fiberglass shards sticking out. The Endeavour was like that. The Amel Sharki is a different class. The overhead has conduit leading from the outside of the void between the cabin overhead and the deck into the void where there are wires to go in. There's plenty of space, but, alas, no way to fishtape from this little conduit nipple to the next. I finally made up a ring slider I could tie the fishtape to and slide it along the existing French wiring in the void to the other conduit nipple on the other end. It serves quite well. The void acts about 1 to 1.5" high over the main salon. Many wires go through there forward and aft. Do you have a strong high-channel-number UHF TV station in your area? Might be fun to play with a portable TV to see how far inside the boat its signal gets, but that's only 1/3 the network's frequency at 800 Mhz. Do cellular phones work inside? Larry W4CSC "Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!" |
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