What pulse width, pixels, zoom, and split screen features mean for sonar use.Sonar is a major component of boating-related fishing activities. To get the most out of this electronic equipment you have to learn to use what you have well. You don’t need to be technically minded to do this, but it helps if you understand sonar’s critical elements and it’s display characteristics. This is also true when you’re evaluating the purchase of sonar.
By Ken Schultz
The Smaller the Pulse Width the Better
Sonar should be able to provide good target resolution, which means not only detecting and depicting all targets, but separating them. When fish that are close together get bunched into one blob of an image, you can’t be sure what’s below, and you lose confidence in the unit.
Cone angle is one of the things that affects resolution, as do pulse width and number of pixels. Pulse is another term for signal, and transducers send out signals at such a superfast rate that a boat cannot outrun them. The distance between signals is known as pulse width. The closer the signals are to each other the better. If the signals are far apart, the distance between them may be greater than the distance between two fish in the cone; as a result, the unit may only mark one fish rather than two (or one fish rather than several). Likewise, if the pulse width is greater than the distance between a fish and the bottom, the sonar will think that the fish is a high spot on the bottom and blend it into the bottom.
Pixels, Zoom, and Split Screen
It is generally thought that the more pixels there are in the liquid crystal display of sonar, the better the resolution, and while this is generally true for midwater viewing, it is not a help for separating fish from the bottom. This is where you need to have, and use, the zoom feature and the split screen mode. Zoom gives you a much better view of the bottom and helps differentiate between fish and the bottom. This is especially helpful if the sonar also has a bottom-tracking function, so it automatically tracks the bottom area. Split screens, however, require larger display area; in units with a small display area, too much can quickly go by, especially if the machine is in fast-scroll mode.
When comparing total number of pixels, realize that vertical pixels matter most. Don’t be concerned about pixels per square inch. A high count in this regard could mask a vertical pixel count that is less than other units. Each pixel in a vertical column represents a certain portion of depth; when there are a lot of vertical pixels, each pixel represents a smaller amount of vertical depth, so it can show more detail. If a unit with 100 vertical pixels is used in 50 feet of water, each pixel represents 6 inches of coverage; if another unit has 200 vertical pixels, each pixel represents 3 inches of coverage in 50 feet of water.
Some anglers think that what is displayed on a sonar screen is a depiction of the entire viewing area beneath the boat. That is not the case when the boat is moving. Although sonar constantly and immediately updates what it detects below, the screen image is built one column at a time. What is happening in real time is displayed at the far right edge of the screen. Everything to the left of that is past history. Thus, when you’re moving, what is directly below you is only shown at the far right of the screen.
Here are a few important things to look for if you’re purchasing new sonar:
- A good backlight for illuminating the screen, and good display characteristics when the light is on.
- An auto-save feature, which means that when the unit is turned off it retains the settings and attributes previously employed.
- Automatic bottom tracking, so the unit constantly adjusts as depth-to-bottom changes.
- A display that can be read from various angles with polarized sunglasses on.
- A screen-save feature so you can save certain views and go back and study them.