A Fish Finder is a subset of a group of instruments
How Fish Finders Work?
A Sonar consists of a transmitter, transducer,
receiver and display.
In the simplest terms, an electrical impulse from a transmitter is converted into a sound wave by the transducer and sent into the water. When this wave strikes an object, it rebounds. This echo strikes the transducer, which converts it back into an electric signal, which is amplified by the receiver and sent to the display. Since the speed of sound in water is constant (approximately 4800 feet per second), the time lapse between the transmitted signal and the received echo can be measured and the distance to the object determined. This process repeats itself many times per second.
The display shows a history of the received echoes. The user can make a number of adjustments to tailor the display to his or her preference, such as senitivity, the depth range and chart speed. Displays use a variety of technologies, provide different resolutions and number of shades of gray or color. Each display is made up of a number of pixels, which are little square blocks that make up the images. The more pixels and shades of gray or color the better resolution and image clarity.
Echoes from fish within the beam will be shown on the display by illuminated pixels. What image appears on the display depends on a number of factors: the sensitivity setting on the fishfinder, the cone angle of the transducer, the speed of the boat, and the size, depth, speed and direction of the fish. A fish that is swimming directly beneath the boat, it will create a consistent echo that will cause a continuous line to appear on the display. A stationary fish caught in a narrow beam transducer appears as a single point on the screen as the boat passes above it, whereas under the same conditions the fish appears as an arch if a wide beam transducer is used.
One of the most common questions is "How do I get fish arches to show on my screen?" It's really pretty simple to do, but it does require attention to detail, not only in the way you make the adjustments to the unit, but to the whole sonar installation.
The number of vertical pixels that the screen is capable of showing is called Screen Resolution. The more vertical pixels on a sonar's screen, the easier it will be for it to show fish arches. This plays an important role in a sonar unit's capability to show fish arches. The chart below lists the pixel sizes and area they represent down to 50 feet for two different screens.
As you can see, one pixel represents a larger volume of water with the unit in the 0 - 100 foot range than it does with the unit in the 0 - 10 foot range. For example, if a sonar has 100 pixels vertically, with a range of 0 - 100 feet, each pixel is equal to a depth of 12 inches. A fish would have to be pretty large to show up as an arch at this range. However, if you zoom the range to a 30-foot zoom (for example from 80 to 110 feet), each pixel is now equal to 3.6 inches. Now the same fish will probably be seen as an arch on the screen due to the zoom effect. The size of the arch depends on the size of the fish - a small fish will show as a small arch, a larger fish will make a larger arch, and so on. Using a sonar unit with a small number of vertical pixels in very shallow water, a fish directly off the bottom will appear as a straight line separate from the bottom. This is because of the limited number of dots at that depth. If you are in deep water (where the fish signal is displayed over a larger distance of boat travel), zooming the display into a 20 or 30 foot window around the bottom shows fish arches near the bottom or structure. This is because you have reduced the pixel size in a larger cone.
The scrolling or chart speed can also affect the type of arch displayed on the screen. The faster the chart speed, the more pixels are turned on as the fish passes through the cone. This will help display a better fish arch. (However, the chart speed can be turned up too high. This stretches the arch out. Experiment with the chart speed until you find the setting that works best for you.)
The transducer is the part of the sonar that sends and receives the sound pulses. The active component in the transducer is commonly referred to as a crystal but actually is a piezoelectric ceramic material. The ceramic material takes the electric transmit signal and transforms it into a mechanical acoustic wave that travels in the water. When the acoustic wave strikes any discontinuity in the water a part of the signal is reflected back to the transducer and since the transducer is reversible (i.e. transforms an electric signal to acoustic signal and vice-versa), it converts that reflected signal back into an electric signal. This signal is sent to the receiver for processing and then on to the display for viewing. A sonar transducer must operate at the same frequency as the unit’s transmitter and receiver,