Article by Capt. Steve Katz
Fine-tuning Your Fishfinder
An echosounder is a type of sonar that transmits sound pulses through the water and listens for that sound to be reflected or echoed off objects below the water’s surface and plots it on a screen. Often called a depthfinder, fish finder or sounder, these machines perform similar functions, showing us what is beneath the surface of the water.
There is a lot of history in the terminology we use to measure the depth of the water; the term sounder was derived from the English word sund, meaning swimming, water and sea.
The depth measurement of a fathom is derived from the old English word faethm, meaning outstretched arms. The original sounder used a sounding line, which is a pre-marked length of weighted rope that was lowered into the water to determine the depth.
Our modern sounders use a lot of electronics including many frequencies and digital signal processing to show us an accurate representation of the underwater world below the boat. Learning how the system works and how to tune the system by adjusting the controls on the display will result in better readings and hopefully allow you to find and catch more fish.
Let’s review some of the basics adjustments that can be done at the display: (Note: not all fishfinders will have all of the adjustments noted below)
Frequency
Most traditional fishfinders (sonar) are dual frequency, meaning they can operate at two frequencies, 200 kHz for shallow water, 50 kHz for deeper water. They can also run under Dual Frequency with both 200 kHz & 50 kHz operating at the same time. If you have a CHIRP system, they have a kHz range they operate within and often one transducer can have two kHz ranges. When operating a fishfinder, you will need to pick a frequency or frequency range you want the display to use, often using two frequencies at the same time gives you the best view of the water and fish below your boat. If you see one of the frequencies providing better results, you can switch to that single frequency or CHIRP range.
Gain
This function is the primary adjustment for sensitivity of the transducer. For example, when the vessel is in 15 feet of water, the device may lose the sonar display and depth. This can occur because too strong of a signal is being received by the transducer due to the shallow depth, and therefore it is unable to read the returning signal. In this case, the "Gain" would need to be reduced on the device. The opposite is true when in deeper water. If your sonar display is not picking up everything you think it should be, such as the bottom or fish deep down, the "Gain” may need to be increased. This setting can often be done automatically by your fishfinder, though you may want to try adjusting it manually to see if you can improve the results.
Range
This function controls the depth range that will be displayed on the screen. If "Range" is set to "auto", the depths on the right side of the display will automatically track the bottom, as long as the other settings are correct. The "Range" can also be manually set to a specific depth.
For example, if searching for structure or fish no deeper than twenty feet, the "Range" could be set to twenty feet. The fishfinder will then only show returns of what is between zero and twenty feet. If adjusting manually, you should adjust the maximum range so that the actual depth /bottom structure is near the bottom of the display screen to provide the best image of the water column. If you are canyon fishing, you many only want to view the top 200-feet, so you would adjust the range as needed for the type of fishing you are doing and not necessarily track the bottom. For the auto range setting to work properly, the gain needs to be adjusted correctly, along with all other settings.
TVG
(Time Variable Gain)
This adjusts the appearance of returns to compensate for weakened sonar signals in deeper water, and reduces the appearance of noise near the surface. When the value of this setting is increased, the echo returns or colors on some machines associated with low-level noise and fish targets appear more consistent through various water depths. This setting also reduces the noise near the surface of the water. A properly adjusted TVG results in targets of the same size producing echoes on the display of the same size, regardless of the depth below the surface.
Interference
Adjusts the sensitivity to reduce the effects of interference from nearby sources of noise.
Bottom Lock
This function allows the undulating bottom to be displayed on the screen as a flat bottom line, while fish above it are shown normally. Hard and raised structure on the bottom will be displayed in reverse, below the bottom drawing. This feature allows you to see only a small amount of depth off the bottom, often adjustable to 0 to 30-feet up from the bottom.
Surface Noise
This hides the surface noise to help reduce clutter. Wider transducer beam widths, usually on the lower frequencies, can show more targets, but can generate more surface noise.
Clutter
The clutter adjustment will make the most of gain settings by eliminating the interference on the screen caused by dense, salty and turbid water. It allows the sounder to increase gain while maintaining a clean, crisp screen with the best ability to show fish. The higher the number, the higher the degree of suppression.
Color Gain
Color gain adjusts the intensity of colors and highlights areas of interest on the sonar screen. This works best after you have adjusted the level of detail shown on the screen using the gain or brightness settings. If you want to highlight smaller fish targets or create a higher intensity display of a target, you can increase the color gain. This causes a loss in the differentiation of the high intensity returns at the bottom. If you want to reduce the intensity of the return, reduce the gain.
Checking and adjusting these controls on your fishfinder will help you get the most out of your fishfinder and your fishing trip.
Captain Steve Katz is the owner of Steve’s Marine Service and holds NMEA, AMEI and NMEA2000 certificates along with ABYC Master Technician certification and factory training from many manufacturers.