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Dialing In

Modern radars like this Raymarine C120 may hide their manual set-up controls behind menus and soft keys, but they are still worth looking for.

If I ever happen to get the chance to play with someone else’s radar, I almost always set myself a challenge: can I get a better picture using manual adjustments than the radar’s automatic systems?

Winning has been getting more difficult over the years, and my latest head-to-head—with a Garmin HD scanner and 5012 multifunction display—ended in a dead heat. But I reckon it’s still worth knowing how to use the old-fashioned manual controls, even if they are buried deep in the menu system.

It’s a bit like using a camera: The “auto” modes are now so good that for most of us, fiddling with them is usually a waste of time. But when the going gets difficult—when you’re trying to photograph a child’s face at a fireworks display or use radar to find a small buoy in a rain storm—the unit’s manual settings come into their own.

Getting the best out of radar is a two-stage process that involves making the most of the tiny scraps of radar energy that are reflected from distant objects or poor reflectors, then removing the clutter that is produced by reflections from things you don’t want to see such as waves and (sometimes) clouds.

Brightness, Contrast, and Color

Brightness, contrast, and color don’t affect the content of the radar picture. But they can decide whether you can see it or not, so they need to be set up before you do anything else, regardless of whether you plan to do the rest of the adjustment by hand or not. The brightness control affects the backlighting of the display and should be set high enough for the picture to be visible but not so high that it is blinding.

Contrast is a feature of monochrome LCD screens fast becoming obsolete in a world of color LCDs. If you’ve got it, adjust it to give you the clearest picture possible, given the direction the light is falling on the screen and the direction from which you are looking at it. Most color displays offer a choice of palettes. Whether you choose yellow blobs on a black background or blue blobs on a white background is mainly a matter of personal preference, but most people prefer a dark background at night.

Gain

The gain control regulates sensitivity. If it’s too high, the screen will be a mass of speckles—the visual equivalent of the noise you hear when you turn up the squelch to high on your VHF radio. If you set the gain too low, your unit will fail to pick up real echoes. As a first step, turn up the gain until the screen fills with speckles, then turn it down until they just disappear from most of the screen. At short ranges, it often pays to turn the gain down a little further to produce a less “blobby” picture, but if you are looking for weak or distant targets, it is worth turning it back up until the speckles start to reappear.

Tuning

Like any radio, a radar receiver needs to be tuned to the right frequency. Al-though a radar is listening for echoes of its own transmissions, the frequency of those transmissions varies slightly as the magnetron warms up and cools down. Luckily, the “auto-tune” facilities of all but the most basic modern radars are very good at finding the right frequency—so good at it that their tuning function is often buried deep in the “installation” part of the menu and used only when the radar is installed or when it has been fitted with a new magnetron.

If you do want to tune by hand—assuming your radar gives you the option of doing so—select a long or medium range and look for a weak contact (blob) on the screen. Then adjust the tuning in small steps (either up or down). Allow about three seconds after each adjustment for the picture to be completely refreshed on the new setting. If the contact gets smaller or weaker, adjust the tuning back the other way until the weak contact is as strong and bright as possible.

This article originally appeared in the August 2009 issue of Power & Motoryacht magazine.

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