Topic: Is an 1198c HD Si REALLY a Di sonar? Maybe it's just me!

[ScottMN]

Here he goes again! But as I was checking out recordings in Humm-Viewer I found something odd but maybe that's what many are trying to tweak on & I didn't get it!
But is an 1198c HD Si REALLY a Di sonar? If you can somehow see these pics you'll see starboard works on Si & Di but not port! Although I think just because of the physics it might bring some port images over and lay them on top of the starboard image. Notice the waypoint & fish on both Di & Si pic, from starboard but can only see the rock on Si Port but won't go over the hump (meaning E to W on this pic). I noticed many more mixed in rocks in Di then Si. Not sure if chart speed has anything to do with it but I was only viewing Si at the time this recording was made. I'll try the pics. You'll have to magnify them I'm sure.

[TroyBoy30]

its actually not a true DI unit, as it makes the DI images from the SI data

[rpro]

Is it accurate to say that the down imaging on these SI units does not represent what is directly beneath the transducer, but that it is off to the right side a little bit and off to the left side a little bit and these views are combined?

[Humminbird_Greg]

That really depend on “Down Imaging Sonar Beam Width” menu setting rpro.  With it set to “Wide” the Di sonar includes all of the left and right Si sonar returns combined together.  With it set to the “Narrow” setting it only shows those sonar returns that are common in both the left and right Si sonar beams.

[rpro]

Thanks Greg. That said, when set to Narrow, is part of the image coming from straight beneath the transducer? Or is there some "blind spot" that is not covered directly under the transducer? Because my brain has been telling me that the left hand looking part of the SI transducer looks to the left and the right hand part looks to the right.

As a second part of the question, is it true that a DI unit does a better job of presenting down imaged stuff than an SI unit does? However you can elaborate on this I would appreciate it, because I've read - probably in some forum at some point - that an SI unit doesn't do a good job of DI and I suppose that is why it is not called an SI DI unit. The down imaging presented by the SI unit is more artificially created or blended I suppose, correct?

Again, my biggest question is "When set to Narrow, is part of the image coming from straight beneath the transducer? Or is there some "blind spot" that is not covered directly under the transducer?"

[Humminbird_Greg]

rpro,
No, there is no “blind spot” under the transducer when using the Si/Di sonar.  This would be true for the Narrow, Medium or Wide Down Imaging Sonar Beam Width settings.  Now at some point near the maximum depth for the Si sonar there would be some blind area but not at the water depths that most fishermen use.

The left Si sonar beam is pointed left (and the right is pointed right) but due to the width of the sonar beams, they extend to underneath the transducer and overlap.

“is it true that a DI unit does a better job of presenting down imaged stuff than an SI unit does?”
I guess that depends on what it is you mean by “better job”.  The DI units show a sharper image but to me I like the 3D like image that the Si units show – personal preference there.  If you want to be able to pick detail out of the sonar image, the DI unit would be the better way to go.

Both types are “artificial” in that it is not naturally occurring.  The Di sonar in the Si units is blended from the Si sonar beam information but that is just how the Engineers decided to display the sonar data.

[ScottMN]

I think of it this way....Si is true Di because when (*oop's,scratch that,) IF 3D view comes in to the public sonar world and everyone has shades with 2 different colored lenses the Si is the closest thing to that now. You really see what is in the water column, plus by learning to read it plus the structure by bottom dimensions, shadows & density.

Try this..draw a circle in the middle of a piece of paper and one out to each side.    o      0      o      Now draw a line perpendicular to the outside dots, through the center dot   --------0--------  Look straight down at it for Si, you have a port (left) & starboard (right) dot. The top is Bow and the bottom is Stern. Then fold it on the line. The half of a dot at the top is your transducer and those two bottom dots on each side are the same but opposite on opposite sides. Sound (sonar) doesn't know that. It just knows how far away and what size and density they are. (If mono sound)  When it comes back to the screen (non-Si) since you see with a single sonar (mono, not stereo) beam what happens? As long as the beams are thin slices it gives you ? Di ?.  If the sound waves are a 360° static cone (2d) you get everything in the cone. Do you know now why a straight object in the water column you are moving toward appears as an ARC?

(Ok, that's what I had to show my wife last night and she spent more time then ever paying attention to fishing ..LOL..Why? She was trying to argue & prove me wrong..ROTFLMAO ) Can't wait to show the Grand Kids! Anyway if you want to get your family interested and excited, show them that and let them think about it. Tie a plastic little fish inside a clear plastic funnel (length-wise sliding on the string) and see if they can draw what it would look like on paper bow to stern, port to starboard. Then do the same inside of a thin clear plastic sandwich container. Good luck getting to look at the sonar next time out though!!

BTW...when is someone going to have 360 imaging for my Terrova? Before mid-May I hope. My whole family can't wait!!! For now I'll have to put a Di transducer on my 3x MinKota stern trolling motor to make it a poor mans, 270° back & forth, imaging. Connect it to my 586i HD DI that should be here today ($250). With an iPilot/iLink remote for the Terrova connected to my 1198c HD Si in my other hand. Hey, wait! That leaves me no hands left for a fishing pole ;-0! I guess that's okay, the family will be with now for that! The wife can't wait to see what they learned!

Well, off to get the new LakeMaster Ver.5 maps for Dakotas! (MN buyers, if you have an older version, check 1st if your lakes have been rescanned,. Many are the same as 2008 but they added some. Big C in Becker Cty. for 1 is way off comparing map to reality,,WAY OFF) Please send me AutoChart Pro or fix it!