Thread: humminbird greg

Am I reading this right in that the down imaging has a wider band than the 2D sonar?

Originally Posted by blairarnold

Am I reading this right in that the down imaging has a wider band than the 2D sonar?

Yes ... Kenny is correct in that a 2d signal produces a circle, while a DI produces a fan shaped cone. A 2d sonar is giving you a 2 dimensional picture of what's within the cone. A DI sonar signal is producing slices thru the water, giving you a closer to 3 dimensional picture. The cone angle degrees are relative to the signal strength, along with the (shape) side to side & front to back width of the coverage area.

The illustration that "rnvinc" has in his post, shows you how each signal is shaped. Take special note of the "Top View of Sonar Beams" illustration ... that shows you what the difference in shape & area coverage is, of a 2d cone (circle) vs a DI cone (fan). The Area of Coverage menu tells you that a DI cone has 3-4 times the left to right angle of coverage, but only 1/3-1/4 the front to rear angle of coverage area. (I believe the front to rear angle is something on the order of 6 degrees of angle).

If memory serves me ... a 60deg cone angle is the widest there is on a 2d unit (triple 20deg cones). But even then, the units are only able to give you a 2d picture. DI units are "scanning" with their narrow depth/wide width cone, and the higher processor power of those units can composite a more 3d version of the signal ... translating the return signal into more of a "picture", than a "representation" (like what you get with the pixel collection of a 2d unit). It's also why DI units need to be moving forward, in order to get the scan info from different angles, and "draw" the more detailed image on the screen.

The more power the unit has (kHz) in the output, and the smaller the pixels (more pixels per given area) ... the more detailed the screen image can be.

* that's the way I understand it, anyway !! I'm no expert on anything, and don't claim to be

... cp