Sonar and DI Dont Show Same Thing?

2d is a cone so some of what you're seeing is in front of the unit while the di is flat and what you are seeing is in the rear view mirror? Depending on which unit you have the 2d cone may differ in size, hugely. 2d is often in 83/200 khz which means 60/20 degree beams but the di units seem to only have 2d in 200/455 khz which means 20/16 degree beams. The SI units seem to have 200/83 2d sonar, have di as well so why not the di? I'm considering some of these same issues so thanks for the post. What unit do you have?

(DI is a thin beam but at 75 degree angle so it's wider than the 60 degree 2d, way wider than the 20 degree 2d)

Another thing to consider is that in the cone shaped 2d format the object is getting pinged multiple times as it moves through the wider cone while in the thin fan shaped DI mode the object gets far fewer pings so the image may not display with the same bulk.

I’m having the exact same issue? If you get it worked out please let me know.

So let's make some distinctions here ...

The OP lists his unit as HELIX 7 SI ...

The only HB SI units that have a dedicated "down pointing" DI piezo are SOLIX, ONIX, and MEGA 9, 10, and 12 ...

All other HB SI units derive the DI view data from the "side pointing" SI piezoes ...

This basically means that any targets directly under the xducer are residing in the outer fringes (less sound strength) of the SI beam sound pulse ...

Simply put - less sound strength area = less echo reflected = less echo data to display in the SI unit DI view ...

Here is the beam form for the right SI pulse showing the Main Axis (strongest part) of the right SI sound pulse ...

Attachment 288544

Mirror the above depiction for the left SI sound pulse and realize than any targets under the boat are just not reflecting as much of the SI sound pulse from that area under the xducer ... Therefore, not as much echo data to display in the HB SI unit DI view ...

Rickie

I've seen some of your comments on GON, you da man. I got a question related to this but I don't want to mess up his thread so I'm posting it. This stuff is like a onion, it just keeps going, just depends on how many layers you need to peal off.

well i just learned something new from Rickie's post.......the 30deg (roughly) angle that side imaging shoots at is from the horizontal top, or water surface. For a couple years now i always thought it was 30deg from horizontal bottom.

Ive experimented with tilting down imaging transducers to the side, but never went past 45deg off horiz bottom thinking surely it wouldnt work :dono

Quote:

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Originally Posted by rnvinc

So let's make some distinctions here ...

The OP lists his unit as HELIX 7 SI ...

The only HB SI units that have a dedicated "down pointing" DI piezo are SOLIX, ONIX, and MEGA 9, 10, and 12 ...

All other HB SI units derive the DI view data from the "side pointing" SI piezoes ...

This basically means that any targets directly under the xducer are residing in the outer fringes (less sound strength) of the SI beam sound pulse ...

Simply put - less sound strength area = less echo reflected = less echo data to display in the SI unit DI view ...

Here is the beam form for the right SI pulse showing the Main Axis (strongest part) of the right SI sound pulse ...

Attachment 288544

Mirror the above depiction for the left SI sound pulse and realize than any targets under the boat are just not reflecting as much of the SI sound pulse from that area under the xducer ... Therefore, not as much echo data to display in the HB SI unit DI view ...

Rickie

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This makes sense. On the DI half of the screen - I get some great images of brushpiles that don't show upon the 2D sonar, also.

Quote:

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Originally Posted by SwampCat

This makes sense. On the DI half of the screen - I get some great images of brushpiles that don't show upon the 2D sonar, also.

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Thus is because that brushpile showing in your DI view (in the HB SI unit) can be in the SI piezo beam form outside of the 2d cone ...

Rickie

Quote:

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Originally Posted by Schins

well i just learned something new from Rickie's post.......the 30deg (roughly) angle that side imaging shoots at is from the horizontal top, or water surface. For a couple years now i always thought it was 30deg from horizontal bottom.

Ive experimented with tilting down imaging transducers to the side, but never went past 45deg off horiz bottom thinking surely it wouldnt work :dono

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The SI beam form is measured horizontal from SI xducer ...

One can see the 30° angle of the SI piezoes in this cutaway ...

Attachment 288562

No DI piezo pointing down ...

Rickie