Navico's Broadband Radar in the Real World
|Navico's Broadband Radar BR24 radome (the Simrad, left) is taller than a digital one because of its two antennas (right) rather than the one in a conventional set, such as Raymarine's (center).|
While the real-world hazard of 2- and 4-kilowatt magnetron pulse radiation is debatable (visit my blog to read the knowledgeable commentary on this topic), other 18-inch radomes do typically come with 2- to 6-foot safe-distance ratings and/or recommendations to mount them overhead. However, while you can safely mount a BR24 most anywhere, you need to consider the unit's several other unusual characteristics before you choose a location.
A magnetron radar simply can't switch from pulse to receive modes fast enough to catch really close-in echo returns. The result is a circle of noise, or filtered blankness, called the "main bang," which typically extends 50 to 100 feet from your radome when it's set at what's usually its tightest range, an eighth of a nautical mile. This dead space gets larger as you range out. By contrast, Broadband Radar's Continuous Wave Frequency Modulated targeting technique transmits and receives simultaneously and has no main bang. And although modern maggies are much improved, C.W.F.M. is also able to resolve range better than magnetron pulses can.
I saw vividly valuable examples of Broadband C.W.F.M. close-range resolution in many situations this summer, including a benchmark experience in Camden's outer harbor, with its hundreds of moored vessels and a busy channel marked only with low, round buoys. I didn't find much use for the BR24's previously unheard of 200- and 300-foot ranges, but I found its 400-foot setting quite handy in thick fog. This range, also expressed as 0.0625 or a sixteenth of a nautical mile, is only seen otherwise on the premium Furuno DRS2D, where it isn't quite as detailed.
However, I got the very best near-range results with the BR24 mounted low on the skiff, regularly nailing small, difficult targets, such as those Camden channel buoys, and holding them until nearly alongside. When installed high on Gizmo's antenna mast, the BR24 lost some of its main-bang-less close-in acuity (due to the 25-degree vertical-beam-width limitation it shares with all radars), and when lowered to the front of the flying bridge, about 14 feet off the water, it couldn't "see" backward through the bridge at all. Other radomes showed some interference when trying to see though the same bridge, or even through my 4-inch-diameter aluminum mast, but none as much as the BR24.
Jesse Deupree reports that a BR24 mounted 12 feet off the water on the stern of his trimaran occasionally picks up his mast or wet sail, though he doesn't find it a bother. I wonder, though, if Deupree would be even happier with his Broadband system if he'd mounted the antenna forward of his mast and lower? I recommend experimenting with BR24 mounting locations before bolting one down. You can, after all, safely hold a running one in your hands.