Thread: Better understanding your sonar

Originally Posted by goodoleboyz250

Ok I was wondering how yall relate your sonar on screen to what's under you. . Say if your using your 60 degree beam and your in 20 fow on a flat. How much actual coverage of the bottom are you getting and how would you relate the objects in screen to where there really are up under you. .maybe yall could use some screen shots to better explain.

I assume this in reference to a 2d sonar 60* beam. In that case, your 20fow would be covered by a cone, that at it's widest bottom coverage would be 20ft in diameter. Or in other words, 10' away from the center point of the circle on the bottom, in every direction; with the center point being a line directly underneath the transducer, going all the way to the bottom.

Figuring "where" within the sonar's cone shaped beam your objects are ... difficult to do, since your unit is rendering a 2d image, on a flat screen, of 3d objects within the confines of the cone. The cone shape of the sonar beam, plus the fact that the sonar ping only tells you how far away the signal reflecting object is from your transducer, means basically that it has to be "somewhere" within the cone's influence or it wouldn't show up ... and doesn't really specify where it's entering the cone's influence. It could just as easily be something right in front of you, that the cone is encountering, as it could be something coming into the cone from any other angle.

A 60deg cone angle shows, roughly, a circle of approximately 1ft wide for every 1ft of depth. So, in 20fow that'd be a 20ft wide circle on the bottom ... at 10ft deep it would be a 10ft wide circle ... at 1ft below the transducer, the circle would be 1ft wide. And you have to understand that these measurements are of a cone shape (slanted outward as you go deeper). Anything entering the cone, that reflects some of the sonar ping, will show on your screen as a return signal, rendered as a pixel or multiple pixels (depending on the number/size of pixels your unit is capable of showing). Since your screen image is flat (2d), it can only show you "when" the object enters the cone & how far away the object is from the transducer. It cannot interpret where the object is, in relation to direction of entry.

Down Image can't tell you, either. Side Image & the 360deg scanning technology units can show you the direction the objects are in relation to your unit's transducer.

This is just how I understand it, and I could be mistaken in some points.

... cp

20 Degree = 200khz

60 Degree = 83khz

Hope this helps !

Brian

Ok thank y'all. Always kind of thought that it was just s guessing game with the 2d and di.. but wasn't sure. That chart helps to

Originally Posted by Brian@BBGmarine

20 Degree = 200khz

60 Degree = 83khz

Hope this helps !

Brian

Great chart Brian...

I'm saving that one...



Rickie

Took me a while to dig that one up. I seem to mis-remember things these days

Good info. Brian. So if you are crappie fishing and your max depth most of the time is 30-40ft.- which would be best to use the 83khz or 200khz.

For me, If I'm vertical fishing, I always stay on 200 khz. For trollling at those depths, you might want to use 83 khz. On side scan /side imaging, I would prefer 455khz for those depths. Personal preference but hopefully others will share their experiences.

Brian

One thing that may help you with where the cover is....as your boat moves, imagine the cone from your sonar moving also. But remember about where the signal hits your screen is hitting the outside of the cone and in the direction you are travelling. If you have a 20' diameter cone, then you have a 10' radius moving with the motion of the boat. Because it is 2d, you won't know if the signal is coming from in front of the boat, or off to the side, but you are within 10' of it in 180°. When the signal is at it's tallest point, you are theoretically closest to the transducer. Hope this makes some sense