This Glossary is presented for informational purposes only. It is intended to provide a brief definition of common terms. For more detail information it is recommended that you visit the manufacturer’s web site for the unit that you are interested.
Actual Sonar Returns: With Fish I.D. off, (if so equipped) fish finders display actual sonar returns, which show likely game fish targets as fish arches. Actual returns also reveal important underwater detail like thermoclines, baitfish and fish movement.
Advanced Signal Processing: Helps you easily spend more time fishing, and less time adjusting sonar sensitivity. With Advanced Signal Proscessing on, it automatically fine-tunes your sonar settings for the clearest, most accurate picture of the underwater world. As water conditions change, it filters out "clutter" that interferes with sonar signals...such as boat speed and suspended particles like algae and plankton...for the best display of fish targets under your boat. NOTE: not all units have this capability.
Alarms: Alarms are designed to alert you to certain sonar "events" by sounding tones. With alarms, you don't need to constantly look at the display, so you spend more time fishing. Many sonars features three main types of alarms, and all are selectable on/off by the user.
- The FISH ALARM alerts you when a fish symbol appears on the screen, with different tones for different sizes of fish targets.
- The ZONE ALARM lets you set an underwater depth zone (e.g. 21 ft. to 53 ft.) and sounds an alarm tone when targets are detected in that zone.
- DEPTH ALARMS are triggered only by signals returning from the bottom. Simply set the depths you want - whether Shallow Alarm, Deep Alarm, or both - and the alarm tone will alert you when the bottom goes shallower, or deeper, than your settings.
Backlight: Selectable on/off illumination that lights both the display and/or keypad on sonar units for enhanced screen viewing when fishing at night and in low light.
Cavitation: It is the sudden formation and collapse of air bubbles in water due to turbulence. If air bubbles pass over the face of the transducer, the signal from the transducer is reflected back by the air bubbles. These reflections are very strong and will result in noise which will interfere with bottom, structure and fish signals, making them difficult or impossible to see.
Chart Speed: The chart is the picture of the underwater world you see on the display, and the chart speed is how fast that picture moves...or scrolls...across the screen from right to left. This scroll speed is adjustable to help display better fish arches...or to suit your viewing preferences when using fish symbols.
Clock: Your local time.
COLOR LINE: On Color capable units it helps separate fish and important structures on or near the bottom from the actual bottom. Since more active-feeding fish hold close to hard bottoms and structures, the color line helps you find more potentially productive water quickly. By comparing color and width you can distinguish between a hard and soft bottom.
Film Super-Twist: Many fish finder units use this technology for liquid crystal displays (LCD). Film Super-Twist provides excellent contrast and readability...in direct sunlight or with the backlight for fishing at night or in low light...and from virtually any viewing angle. Film Super-Twist screens are also easy to see with polarized sunglasses.
Fish Arches: With Fish I.D. off, sonar units display underwater fish targets in the shapes of "boomerangs" or fish arches. As with fish symbols, the larger the return echo of the suspended fish target, the larger the fish arch.
Fish Symbol I.D.: It's what many anglers say is the easiest way to identify fish targets on their SONAR units and is ideal for fishing shallow water. With Fish I.D. on, it automatically interprets sonar echos and displays them as fish symbols. The fish symbols are displayed in up to four different sizes to match the relative size of the target echo. With Fish I.D. off, and showing actual sonar returns, targets are displayed as fish arches. NOTE: not all units have this capability.
FREQUENCY: The length of a sound wave, usually measured in Kz (Kilo Hertz/Second) and is measured from wave peak to wave peak. As an example: a 200 Kz signal will be transmitted 200 times per second.
GRAYLINE: A general term that was originally patented by Lowrance helps you distinguish between hard and soft bottoms, where the thicker the gray band, the harder the bottom. Grayline also helps separate fish and important structures on or near the bottom from the actual bottom. Since more active-feeding fish hold close to hard bottoms and structures, Grayline helps you find more potentially productive water quickly.
Noise: Noise is visual "clutter" that appears on the display. It's caused by too many undesirable signals being picked up by the fish finder (typically from electrical sources such as trolling motors, alternators, spark plugs, radio transmitters, water turbulence, etc.). Manually adjusting the sensitivity helps fine-tune the sonar to show the most detail with the least noise. Use the automatic sensitivity adjustments for the best picture possible.
Output Power: The amount of electrical energy applied to the transducer by the sonar transmitter. Expressed in watts, typically the higher the output power the sonar unit has, the deeper it can penetrate, and the finer the detail that can be shown.
Peak-to-Peak: Normally used to describe the output power of a sonar transmitter. This value is a measurement of the total swing of an AC voltage from its peak negative value to its peak positive value.
Pixels: These are "picture elements," or little squares of color that come together to form shapes and images on a liquid crystal display (LCD). The more pixels per square inch, the sharper and more detailed picture you see.
Programmable Windows: The ability to customize a split-panel window display to provide two views of the sonar information. Example: One window may be set to track the water column from the bottom up to 10 feet and the other could be set for either the entire water column from the bottom up or some other determined range between the bottom and the top.
Pulse Length: The length of time a sonar unit transmits a pulse of sound into the water. Sometimes referred to as Pulse Width.
Range: Range is the depth of the water column - from the surface down - displayed on the sonar screen. Most units will automatically adjust the range to keep the bottom (and depth shown in feet or meters) displayed in the lower part of the screen. There's may also be a manual mode where anglers can select the range they want to view from a menu of depth choices.
RMS: Literally "root mean square." A DC voltage that will produce the same heating effect (power output in Watts) as the AC voltage. For a sine wave, the RMS value is equal to 0.707 times the peak value of an AC voltage. Example:divide Peak-to-Peak by 2 (or in half) and multiple by 0.707 = RMS voltage.
Sensitivity: This is a manual adjustment that allows users to fine-tune the fish finder to see the most underwater detail with the least visual noise. For anglers who'd rather spend more time fishing than adjusting, many units does this automatically.
Speed/Temp: Using special sensors, many units can digitally display surface water temperature, boat speed and distance log (odometer) in addition to showing the depth range. Serious anglers, especially tournament pros, use speed and temperature information as aids in their fishing strategies. Note: displaying speed is used mainly for trolling purposes, and may not work at "top-end" boat speeds.
SONAR: Acronym for “SOund, Navigation And Ranging”.
Structure: Structure is basically all solid objects rising from the bottom of a lake or river that isn't part of the actual bottom...like sunken trees, brush and rock piles...which creates habitats, feeding grounds and cover for game fish. For locating and separating close-holding fish from structure, Grayline or Color Line is the preferred choice of more anglers.
Thermo Cline:These are areas underwater where warmer layers of water meet cooler layers, and where fish are often active. Generally, baitfish hang just above the thermo cline, while larger game fish are found suspended in or just below it. Most units will display thermo clines when used in the manual mode, showing actual sonar returns, and with the sensitivity set correctly.
Transducer: The part of the fish finder that functions like an antenna to send out sonar signals (sound waves) and receive return echoes that are displayed as pictures on the sonar screen. Lowrance transducers can be attached to the transom or inside the hull of a boat, or even to a trolling motor using a special mounting.
Zoom: With zoom, you can enlarge the sonar display for a closer look at small detail and fish target signals. In the sonar automatic zoom mode, the bottom is constantly tracked and displayed in the lower portion of the screen (also called "zoom bottom track"). In the manual zoom mode, you can create a zoom "window" of any size, and move it anywhere up or down in the sonar water column...it doesn't remain locked on to display the bottom.
