Point of Contact
Radar has been around for more than 100 years and has progressed from being a scientific novelty to becoming the most versatile of marine electronics. You can use radar to find out where you are, to find your way into unfamiliar harbors, to dodge thunderstorms, or even to find fish by picking out flocks of feeding seabirds. By far its most important use it that for which it was first intended—collision avoidance.
Radar works by transmitting short, intense pulses of radio energy, then listening for the faint echoes that come back. Using radar effectively is a multi-stage process that involves making the most of the tiny scraps of energy that are reflected from distant objects or poor reflectors, then removing the clutter that is produced by reflections from things we don’t want to see, such as waves and sometimes clouds. After that, you can start on the third stage—interpreting the useful information you have received.
THE RIGHT SETTINGS
Brightness, contrast and color: These elements help you see contacts more clearly, so they need to be set up properly. Set the brightness control high enough for the picture to be visible, but not so high that it is dazzling. If you still have a unit with a monochrome display, adjust the contrast so it gives the clearest picture possible. Most color displays offer a choice of color palettes, and which one you choose is up to you. Most people prefer to have a dark background at night.
Gain: The gain control adjusts the receiver’s amplification. If gain is set too high, the screen will be filled with a mass of speckles. This is the visual equivalent of the noise you hear when the squelch control is wrongly adjusted on a radio. If it is set too low, real echoes will be missed.
First, increase the gain control until the screen is full of speckles, then reduce it until the speckles have disappeared from all but the center of the screen. At short ranges, it often pays to turn the gain down a little further, because this produces a less “blobby” picture. When looking for weak or distant targets, turn it back up until the speckles start to reappear.
Tuning: Even though a radar listens for the echoes of its own transmissions, the receiver still needs to be tuned to the right frequency. Luckily, the “auto-tune” function on most modern radar sets is very good at doing this. If you want, or need to, tune your set by hand, set the gain first, then select a long or medium range and look for a weak contact on the screen. Next, adjust the tuning in small steps, either up or down, waiting about three seconds after each adjustment for the picture to be completely redrawn under the new setting. If the contact looks weaker, adjust the tuning back the other way. Keep going until the contact is as strong and bright as possible.
Clutter control: Some things produce echoes we don’t really want to see. Seawater, in particular, is such a good reflector that the center of a radar screen is often packed with big bright blobs generated by the radar energy being reflected from waves immediately around the boat. The sea-clutter control can remove these blobs, but it’s a crude tool that can also erase boats, buoys and even land.
To be sure it is working effectively, turn the sea-clutter control down to its minimum setting. That way you will know it’s doing no harm. Then, if sea clutter truly is a problem, you can turn the clutter control back up, as little as possible.
Finally, there is the interference-rejection control that erases visual clutter caused when your radar receives transmissions from another boat’s radar. This control can do nothing but good, so there’s no point in switching it off.
Rain-clutter controls can be equally dangerous. While they do remove smudgy contacts created by rain clouds, they also degrade echoes from genuine targets. The rule of thumb here is the same as for the sea-clutter control: turn it off when you don’t need it, and then use it as sparingly as you can.
Some radars have two rain-clutter controls, one usually affects only the area in the middle of the screen, while the other, often called “FTC,” affects the entire scanning area.