Water temperature has an important influence upon the activities of all fish. Fish are cold-blooded and their bodies are always the temperature of the surrounding water. During the winter, colder water slows down their metabolism. At this time, they need about a fourth as much food as they consume in the summer.
Most fish don't spawn unless the water temperature is within rather narrow limits. The surface water temperature gauge built into many of our sonar units helps identify the desired surface water spawning temperatures for various species. For example, trout can't survive in streams that get too warm. Bass and other fish eventually die out when stocked in lakes that remain too cold during the summer. While some fish have a wider temperature tolerance than others, each has a certain range within which it tries to stay. Schooling fish suspended over deep water lie at the level that provides this temperature. We assume they are the most comfortable here.
Lowrance liquid crystal graph marking a thermocline on Skiatook Lake near Tulsa, in Oklahoma, between 40 and 50 feet of water. Notice how the thermocline stays consistent across the body of water regardless of bottom contour.
The temperature in a lake is seldom the same from the surface to the bottom. Usually there is a warm layer of water and a cooler layer. Where these layers meet is called a thermocline. The depth and thickness of the thermocline can vary with the season or time of day. In deep lakes there may be two or more thermoclines. This is important because many species of game fish like to suspend in, just above, or just below the thermocline. Many times bait fish will be above the thermocline while larger game fish will suspend in or just below it. Fortunately, this difference in temperatures can be seen on the sonar screen. The greater the temperature differential, the denser the thermocline shows on the screen.
http://www.fishfindergarage.com/
Showing posts with label Lowrance fish finders. Show all posts
Showing posts with label Lowrance fish finders. Show all posts
Friday, March 6, 2009
Friday, February 27, 2009
Transducer Cone Angles
The transducer concentrates the sound into a beam. When a pulse of sound is transmitted from the transducer, it covers a wider area the deeper it travels. If you were to plot this on a piece of graph paper, you would find that it creates a cone shaped pattern, hence the term "cone angle." The sound is strongest along the center line or axis of the cone and gradually diminishes as you move away from the center.
In order to measure the transducer's cone angle, the power is first measured at the center or axis of the cone and then compared to the power as you move away from the center. When the power drops to half (or -3db[decibels] in electronic terms), the angle from that center axis is measured. The total angle from the -3db point on one side of the axis to the -3db point on the other side of the axis is called the cone angle.
This half power point (-3db) is a standard for the electronics industry and most manufacturers measure cone angle in this way, but a few use the -10db point where the power is 1/10 of the center axis power. This gives a greater angle, as you are measuring a point further away from the center axis. Nothing is different in transducer performance; only the system of measurement has changed. For example, a transducer that has an 8 degree cone angle at -3db would have a 16 degree cone angle at -10db.
Although the half power point is the standard for measuring cone angles, fish detection angles are much larger. Lowrance sonar units have very sensitive receivers and can detect return echoes from fish, structure or the bottom out to 60° or more. This means that the fish detection angle is 60° even though the cone angle is only 20°.
20 degree cone angle | 8 degree cone angle
Lowrance offers transducers with a variety of cone angles. Wide cone angles will show you more of the underwater world, at the expense of depth capability, since it spreads the transmitter's power out. Narrow cone angle transducers won't show you as much of what's around you, but will penetrate deeper than the wide cone. The narrow cone transducer concentrates the transmitter's power into a smaller area. A bottom signal on the sonar unit's display will be wider on a wide cone angle transducer than on a narrow one because you are seeing more of the bottom. The wide cone's area is much larger than the narrow cone.
High frequency (192 - 200 kHz) transducers come in either a narrow or wide cone angle. The wide cone angle should be used for most freshwater applications and the narrow cone angle should be used for all saltwater applications. Low frequency (50 kHz) sonar transducers are typically in the 30 to 45 degree range. Although a transducer is most sensitive inside its specified cone angle, you can also see echoes outside this cone; they just aren't as strong. The effective cone angle is the area within the specified cone where you can see echoes on the display. If a fish is suspended inside the transducer's cone, but the sensitivity is not turned up high enough to see it, then you have a narrow effective cone angle. You can vary the effective cone angle of the transducer by varying the receiver's sensitivity. With low sensitivity settings, the effective cone angle is narrow, showing only targets immediately beneath the transducer and a shallow bottom. Turning the sensitivity control up increases the effective cone angle, letting you see targets farther out to the sides.
http://www.fishfindergarage.com/
In order to measure the transducer's cone angle, the power is first measured at the center or axis of the cone and then compared to the power as you move away from the center. When the power drops to half (or -3db[decibels] in electronic terms), the angle from that center axis is measured. The total angle from the -3db point on one side of the axis to the -3db point on the other side of the axis is called the cone angle.
This half power point (-3db) is a standard for the electronics industry and most manufacturers measure cone angle in this way, but a few use the -10db point where the power is 1/10 of the center axis power. This gives a greater angle, as you are measuring a point further away from the center axis. Nothing is different in transducer performance; only the system of measurement has changed. For example, a transducer that has an 8 degree cone angle at -3db would have a 16 degree cone angle at -10db.
Although the half power point is the standard for measuring cone angles, fish detection angles are much larger. Lowrance sonar units have very sensitive receivers and can detect return echoes from fish, structure or the bottom out to 60° or more. This means that the fish detection angle is 60° even though the cone angle is only 20°.
20 degree cone angle | 8 degree cone angle
Lowrance offers transducers with a variety of cone angles. Wide cone angles will show you more of the underwater world, at the expense of depth capability, since it spreads the transmitter's power out. Narrow cone angle transducers won't show you as much of what's around you, but will penetrate deeper than the wide cone. The narrow cone transducer concentrates the transmitter's power into a smaller area. A bottom signal on the sonar unit's display will be wider on a wide cone angle transducer than on a narrow one because you are seeing more of the bottom. The wide cone's area is much larger than the narrow cone.
High frequency (192 - 200 kHz) transducers come in either a narrow or wide cone angle. The wide cone angle should be used for most freshwater applications and the narrow cone angle should be used for all saltwater applications. Low frequency (50 kHz) sonar transducers are typically in the 30 to 45 degree range. Although a transducer is most sensitive inside its specified cone angle, you can also see echoes outside this cone; they just aren't as strong. The effective cone angle is the area within the specified cone where you can see echoes on the display. If a fish is suspended inside the transducer's cone, but the sensitivity is not turned up high enough to see it, then you have a narrow effective cone angle. You can vary the effective cone angle of the transducer by varying the receiver's sensitivity. With low sensitivity settings, the effective cone angle is narrow, showing only targets immediately beneath the transducer and a shallow bottom. Turning the sensitivity control up increases the effective cone angle, letting you see targets farther out to the sides.
http://www.fishfindergarage.com/
Monday, February 16, 2009
Sonar tutorial for Lowrance and how it works
Sonar Tutorial
People have been fishing for thousands of years. Every person fishing has had the same problem - finding fish and getting them to bite. Although sonar can’t make the fish bite, it can solve the problem of finding fish. You can’t catch them if you’re not fishing where they are - and the Lowrance sonar will prove it
In the late 1950s, Carl Lowrance and his sons Arlen and Darrell began scuba diving to observe fish and their habits. This research, substantiated by local and federal government studies, found that about 90 percent of the fish congregated in 10 percent of the water on inland lakes. As environmental conditions changed, the fish would move to more favorable areas. Their dives confirmed that most species of fish are affected by underwater structure (such as trees, weeds, rocks, and drop-offs), temperature, current, sunlight and wind. These and other factors also influence the location of food (baitfish, algae and plankton). Together, these factors create conditions that cause frequent relocation of fish populations.
During this time, a few people were using large, cumbersome sonar units on fishing boats. Working at low frequencies, these units used vacuum tubes which required car batteries to keep them running. Although they would show a satisfactory bottom signal and large schools of fish, they couldn’t show individual fish. Carl and his sons began to conceptualize a compact, battery operated sonar that could detect individual fish. After years of research, development, struggle and simple hard work, a sonar was produced that changed the fishing world forever. Out of this simple beginning, a new industry was formed in 1957 with the sale of the first transistorized sportfishing sonar. In 1959, Lowrance introduced “The Little Green Box,” which became the most popular sonar instrument in the world. All transistorized, it was the first successful sportfishing sonar unit. More than a million were made until 1984, when it was discontinued due to high production costs. We’ve come a long way since 1957. From “little green boxes” to the latest in sonar and GPS technology, Lowrance continues to lead in the world of sportfishing sonar.
How it Works
The word "sonar" is an abbreviation for "SOund, NAvigation and Ranging." It was developed as a means of tracking enemy submarines during World War II. 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 frequencies most often used by Lowrance in our sonar are 192 - 200 kHz (kilohertz); we also make some units that use 50 kHz. Although these frequencies are in the sound spectrum, they’re inaudible to both humans and fish. (You don’t have to worry about the sonar unit spooking the fish - they can’t hear it.)
As mentioned earlier, the sonar unit sends and receives signals, then “prints” the echo on the display. Since this happens many times per second, a continuous line is drawn across the display, showing the bottom signal. In addition, echoes returned from any object in the water between the surface and bottom are also displayed. By knowing the speed of sound through water (4800 feet per second) and the time it takes for the echo to be received, the unit can show the depth of the water and any fish in the water.
http://www.fishfindergarage.com/
People have been fishing for thousands of years. Every person fishing has had the same problem - finding fish and getting them to bite. Although sonar can’t make the fish bite, it can solve the problem of finding fish. You can’t catch them if you’re not fishing where they are - and the Lowrance sonar will prove it
In the late 1950s, Carl Lowrance and his sons Arlen and Darrell began scuba diving to observe fish and their habits. This research, substantiated by local and federal government studies, found that about 90 percent of the fish congregated in 10 percent of the water on inland lakes. As environmental conditions changed, the fish would move to more favorable areas. Their dives confirmed that most species of fish are affected by underwater structure (such as trees, weeds, rocks, and drop-offs), temperature, current, sunlight and wind. These and other factors also influence the location of food (baitfish, algae and plankton). Together, these factors create conditions that cause frequent relocation of fish populations.
During this time, a few people were using large, cumbersome sonar units on fishing boats. Working at low frequencies, these units used vacuum tubes which required car batteries to keep them running. Although they would show a satisfactory bottom signal and large schools of fish, they couldn’t show individual fish. Carl and his sons began to conceptualize a compact, battery operated sonar that could detect individual fish. After years of research, development, struggle and simple hard work, a sonar was produced that changed the fishing world forever. Out of this simple beginning, a new industry was formed in 1957 with the sale of the first transistorized sportfishing sonar. In 1959, Lowrance introduced “The Little Green Box,” which became the most popular sonar instrument in the world. All transistorized, it was the first successful sportfishing sonar unit. More than a million were made until 1984, when it was discontinued due to high production costs. We’ve come a long way since 1957. From “little green boxes” to the latest in sonar and GPS technology, Lowrance continues to lead in the world of sportfishing sonar.
How it Works
The word "sonar" is an abbreviation for "SOund, NAvigation and Ranging." It was developed as a means of tracking enemy submarines during World War II. 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 frequencies most often used by Lowrance in our sonar are 192 - 200 kHz (kilohertz); we also make some units that use 50 kHz. Although these frequencies are in the sound spectrum, they’re inaudible to both humans and fish. (You don’t have to worry about the sonar unit spooking the fish - they can’t hear it.)
As mentioned earlier, the sonar unit sends and receives signals, then “prints” the echo on the display. Since this happens many times per second, a continuous line is drawn across the display, showing the bottom signal. In addition, echoes returned from any object in the water between the surface and bottom are also displayed. By knowing the speed of sound through water (4800 feet per second) and the time it takes for the echo to be received, the unit can show the depth of the water and any fish in the water.
http://www.fishfindergarage.com/
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