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Marine Radar Explained

When purchasing marine radar there are several considerations. Marine radar is probably the best piece of marine electronics to have. Of course if you are sinking, you want a marine radio and an EPIRB. But for most of your boating, we hope that you don’t sink, and just find yourself in the dark or in the fog. Marine radar lets you see through the fog. Performance and reliability of marine electronics is critical. Performance of marine radar is largely determined by two factors, power and horizontal beam width.

Power is the obvious one. A 4K (4000 watt) marine radar is better than a 2K(2000 watt). A 6K(6000 watts) marine radar is better yet. This is because radar sends a pulse, then listens for an echo. A lower power marine radar is like a small child yelling into a canyon and listening for the echo. A high power marine radar is like a large opera singer yelling into the canyon. Obviously it is easier to hear the louder echo. The same is true for marine radar. More power means more range and better penetration through moisture laden air. But power in a marine radar is not the only factor to consider when buying a marine radar.

Horizontal Beam Width trumps power because it concentrates the power. To understand beam width, a water analogy is best. Marine radar transmits a pulse of energy. This pulse has a shape, that is the radar energy is concentrated in some space. Think of it as a hose spraying water. You spray the water out and listen for splash back(echoes). When a marine radar has a wide horizontal beam width, say 6 degrees), it is like a hose with a wide spray pattern. A smaller beam width, say 1.2 degrees is like a hose with a concentrated spray. Of course with marine radar it is somewhat more complex, but is you think of the transmitted lobe from the ships radar as a pulse of water shot from a hose, then the tighter the spray nozzle, the more likely you will get splash back from a nearby object. If the hose has a wide spray pattern, more water is wasted the the side of an object and much less water hits the object at any time.

The water in the hose analogy also explains why horizontal beam width also affects target resolution. When a marine radar is working, it is like a man with a hose, spinning on top of your boat. He is dry, because he only gets wet when water is splashed back on him. If he turns his spray nozzle wide, he gets very little splash back, but if he turns it tight, with a concentrated steam of water, he get a lot more wet. When marine radar works, it doesn’t send a steam, it sends a pulse. So think of the hose being turned on and off a thousand times per revolution. The pulse of water is like a marine radar pulse. It leaves the hose and travels across the air until it hits an object. It is easy to understand how a more concentrated pulse will reflect back better, but a tighter pulse is also better able to tell things apart. If you have two posts next to your boat that are say ten feet apart, when you spay with a wide nozzle, there is no time when the spray goes between the posts without hitting them. A concentrated pulse may hit the first post, the go between them and then hit the second post. So for marine radar, this is like two kayaks a mile off the bow. The marine radar with a wide horizontal beam width will paint this as one target, but the marine radar with the narrow horizontal beam width will paint it as two separate targets. Horizontal Beam Width in marine radar runs from about one to six degrees. A marine radar with less than a one degree beam width is out of sight expensive and a marine radar with over a six degree beam width should not be considered. With all else equal. less is better in horizontal beam width and more is better for power.

Marine radar systems are more complicated than the analogies given above. Pulse repetition rate and pulse width are factors to consider. For the hose analogy, these are how often you turn off and on the hose and how long you leave the hose on.
Interestingly, mother nature has assured that larger antennas have smaller tighter beam widths. Thats why the open array antennas are so good. It is not because they are open array, it is because the are big. Is bigger better? Yes, in marine radar antennas, power output and display size. Marine electronics and marine radar enhance the safety of your vessel. Call TMS, Technical Marine at 847-746-0100. The marine radar is the heart of you marine electronics.

Marine Radar

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