Marine Radar Systems Explained

Marine Radar Systems Get Smaller, More Powerful

mounted marine radar

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mounted marine radar.

Navico Broadband Radar is arguably the most significant recent technological advance in marine radar electronics. But can it actually help you to, say, negotiate a daunting Downeast mix of chowder-thick fog, granite islets, and lobster boats that go every which way while tending a minefield of potentially prop-snagging trap buoys? I set out to answer that question and ended up feeling like the lone laughing man in the famous Charles Addams cartoon of an otherwise horrified horror movie audience (yes, kids, that's the same sick wit behind the "Addams Family" TV show). The horror of 2009 was the wettest, foggiest Maine summer in most any cruiser's memory, which in my case meant the best making-it-real radar-testing season in 38 years of exploring this gorgeous, if challenging, coast. Honestly, I tried to hide my glee!

And, boy, did I learn a lot. The BR24 radome-which I tested with both Lowrance HDS-10 and Simrad NX45 multifunction displays, and which also works with other Navico brands and models (www.navico.com)-truly did take a lot of stomach churn out of the situation sketched above. In fact, at one point I was ready to call it the best 18-inch radar I'd ever used. But that was before I tried it alongside Raymarine's new Digital 18-inch radome(www.raymarine.com), which, in some ways, is better still. While the RD418D still uses a traditional pulse magnetron, Raymarine has added so many signal processing advancements that the resulting target resolution is a world apart from the blotchy crudeness of older radomes. But even if the targeting performance of the two little domes was pleasingly similar in many situations, other aspects are notably different.

You'll know a BR24 is unique a few seconds after you turn it on, because that's all it takes for its silicon transceiver to start painting targets. The RD418D, by contrast, takes 70 seconds to warm up its magnetron. And that magnetron is a lot more power thirsty than the BR's semiconductors, lapping up 20 watts in standby and 40 in use, while the BR claims 1.6 watts in standby and 17 in use. Those numbers are particularly important on a sailboat, of course, but sometimes powerboats are energy sensitive too, like when using radar to monitor anchor drag in a quiet harbor. Hot magnetrons are also known to fail sometimes, and BR may well turn out to be a more trouble-free technology.

Then there's the matter of BR's extraordinarily low RF emissions. Navico has called Broadband "a huggable radar" without any radiation hazard whatsoever, but the boast is somewhat controversial. While no one doubts BR's innate safeness, some wonder if regular magnetron radomes aren't equally benign. You can find some knowledgeable discussion about this at my blog, but you'll also learn that the science is mighty murky. Personally, I'm comfortable with the fact that the FCC has certified Broadband as safe for humans at zero distance, and note that Raymarine and other manufacturers of magnetron radomes recommend above-head-level installs for marine radar. Thus, BR is particularly suitable for small boats like tenders, and also lends itself to lower-than-normal installations on larger boats, which is important because of its particular performance strengths.

In fact, I first mounted the BR24 on my 14-foot power catamaran, just five feet above the water, and the close-range performance was astonishing. The HDS-10 could clearly target kayaks, even water-skiers, a few hundred yards away and could hold onto low, round channel markers until I was nearly alongside them. While the horizontal resolution of all 18-inch radars is limited by a beamwidth of about five degrees, Broadband's low-power CWFM targeting technique-that's Continuous Wave Frequency Modulated-permits high nearby range resolution while also eliminating the problem of very close-in noise. That noise (sometimes alternately seen as a blank area around your own boat) is caused by the fact that magnetron radars simply can't send a pulse and then receive its echo back fast enough. The BR24 actually has separate transmitting and receiving antennas-hence, the radome's unusual height-and doesn't pulse anyway. CWFM means that it transmits a continuous signal which changes frequency over a set time period, and then determines target range by measuring the echo return of a specific frequency rather than a pulse. It's an entirely different way to do business, and it works especially well in tight quarters.

At any rate, when I mounted the BR on Gizmo's mast, about 22 feet above the water, I immediately noticed a slight decrease in its extreme near-range abilities, a change I don't think I'd notice on any other radar, even if it offered BR's unheard of 300- and 200-foot range settings. I don't want to overemphasize the value of this performance attribute, but it's valuable in some situations and I'm expecting to find a sweet spot when I move the BR scanner to a lower position in front of my flying bridge. I'll report on the results next month, along with a comparison to the Garmin 18HD radome (www.garmin.com) that will take the BR's former position in marine radar technology.

I am not expecting the moved Broadband to lose any long-range abilities, because frankly it doesn't seem to have the power to see as far as the higher line of sight permits. The 24 in BR24 denotes the scanner's theoretical maximum range, but it seems more theoretical than most. While I have seen it bring in a bold headland at 10 miles and the broad side of a ship at five, the Raymarine RD418D-which pumps out a full 4 kilowatts, and claims 48-mile theoretical range-is quite noticeably better at these ranges.

But needed radar range is somewhat subjective, and the compelling factors have changed over the years. AIS, radar overlay, satellite weather radar overlay, and GPS chart plotters themselves have all conspired to make high-resolution, long-range marine radar less critically important. Not that I wouldn't have one, especially offshore and especially fishing. If you have the space and wherewithal, big radars are better in most every way, and the newest ones better still. However, during my recent testing cruises I've only zoomed out above the four-mile range to see how well it worked, and both little radomes performed more than adequately in the much lower ranges we mostly used as we groped the coast.

The big surprise was how tightly and clearly the little Raymarine resolved closerange targets, even the mass of moored and moving vessels that can unnerve folks entering my harbor in restricted visibility. It's not as good as the BR, but it's close. A few of the RD418D's specs-like its ability to switch through eight pulse lengths as you range in and out-suggest how it circumvents the traditional limitations of small magnetron radars, but I suspect that most of the magic lays under that vague term "digital." Like "high definition" and its variants-SHD, UHD, xHD, etc.-the term is meaningless in terms of radar specifications, but it sure means something. Marine electronics engineers are definitely figuring out how to get microprocessors and software to distinguish real targets from noise and make the most of them. It's worth noting, for instance, that the screen images shown here were taken with the radar settings on auto. I tried manual tuning both radars, but it's darn hard to outsmart these new machines.

So what my testing has revealed so far is two remarkably good, if technically quite different, radomes. And given the high performance Raymarine has squeezed out of 18-inch magnetron technology, I'd guess that Furuno-widely acknowledged as king of the large radar hill-gets at least similar results out of its latest UHD 19-inch radome(www.furunousa.com) based on what I've seen from the latest incarnations of their larger models, as may others like Garmin. In other words, if you have a radar that doesn't easily and clearly show you all the boats, buoys, and shorelines you need to know about when the visibility gets dicey, it may be time to upgrade. The BR24, incidentally, lists for $1,849 to $2,099, depending on brand, while the RD418D goes for $1,480.

Of course, there's more to a marine radar shopping decision than target performance. For instance, neither of the Navico MFDs I tried can use Broadband Radar to track moving targets (the MARPA function), though I suspect that BR resolution could make that useful feature work well. In fact, there are many subtleties to how an MFD presents and controls a radar scanner, some of which I'll discuss next month. One thing I can tell you for sure: If you spend some time driving around in the fog with three or four different marine radar/ MFD systems, you see a lot.

Editor's Note: Next month, the "Electronics" column about small radar continues with a discussion of features beyond performance and hands-on tests of units from Garmin and Furuno.