But for now suffice it to say that another feature of a bridge is that it lets you have one large data network split into two (or more) independent impedance environments.Īt any rate, this stuff can get real when you create an extra large N2K backbone and/or get involved with some of the more finicky devices. I really should write an entry around Rich’s rap, because he can really give the technology life and help folks understand why care must be taken (especially with the large networks Maretron sometimes works with). Somewhere I have a recording of Maretron CEO Rich Gauer waxing eloquent about how N2K is an impedance-based network protocol, how well the data waves travel through the backbone as long as the cable and connector characteristics are correct and the terminating resistors are there to prevent back splatter (my phrase), how the drop lengths need to be limited to minimize data wave reflections, and how the usually robust process can get screwed up by impedance-related subtleties. They’re reborn! Which may not mean much until you start to grasp why an N2K network has a limited number of nodes, limited backbone length, and a limited total drop length, which has nothing to do with the limited capacity of the power wires carrying 12v to the nodes, and little to do with even the bandwidth of the data wires. In other words, the PGNs are read by a microprocessor and then re-broadcast fresh on the other network. The critical concept, I think, is that this bridge doesn’t just pass data from one network to another, but “copies” it. But the Mystic Valley brochure (unfortunately not online yet) goes on to claim that the bridge can also be used to increase the number of devices and drop lengths beyond what’s allowed for a single backbone. Mystic Valley Communications, the small company that produced the prototype above, describes its bridge as an “intelligent connection between two electrically isolated NMEA 2000 networks that copies transmitted data between the two networks.” Obviously, then, this is another way to deal with the backbone power issues discussed here in the past with a bridge you can have two N2K networks that act as one in terms of data but are independent in terms of supplying power to devices, and in terms of a power failure. So what the dickens is a NMEA 2000 bridge and why would you want one? Well, I think the answers are complicated enough, and important enough, that they deserve two entries.
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