    
Woodlander
Senior Member
Username: Woodlander
Post Number: 2158
Registered: 02-2003
| | Posted on Sunday, August 02, 2009 - 05:00 pm: | 
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Part II
How depth finders work
It sounds silly because you don’t have to know how a computer or a television works to use them but a good understanding of how sonar works will make reading them much easier. Everybody pretty much use the term “depth finder” now inside of “fish finder” because that’s what they are. We use them to find more than just fish.
A depth finder is composed of a transducer that sends and receives sound waves, a central processing unit that collects the data from the transducer and analyzes it, and a liquid crystal recorder onto which the analyzed data is displayed in a manor that we can understand.
The transducer is constantly and rapidly sending out sound waves. When the sound waves hit an object or the bottom they are reflected back to the transducer. All things being equal objects that are closer, bigger, or denser will show up differently from ones farther away, smaller, or less dense. When the sound waves hit something really solid the unit records that depth as the bottom. Every now and then over a thick brush pile or a dense school of bait fish you can actually get a false bottom read. I’ll cover that in another section.
Like a rock dropped in the water the sound waves go out in all directions - 180 degrees. The strongest signals go straight down. They also fan out and get weaker as they go out and up.
These two pictures will show roughly the area that a sound wave will cover as it leaves the transducer. Think of the boat floating in a giant vase.
The first one shows what a side view would look like with the boat at the top.
This one would be an aerial view.
I’ll explain the blue and yellow in the next section.
Next one up shortly - Part III
How objects are displayed on the screen
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