Confused

[gotta_fish]

Ok im alittle confused on what freq. to use on di/ si I have a 998 hd si I fish on Norman mostly in water ranging from 15 to 50 ft. I've got some decent images but which freq works best for DI and Si I set my si range to around 85 foot . Maybe I need to give more info. Ive looked on you tube and scanned a lot of these archives for info . Thanks in advance .

[rnvinc]

Frequency choice is dependent on what task you need to do at the moment...

Because the 455kHz is 180° coverage to the surface on both sides...it is best for finding suspended fish out to sides where the upper reaches of the beams can catch the suspended fish...the trade-off for 455kHz is that the image will be a little fuzzier...

Conversely...because the 800kHz is higher frequency.....it is best for discerning detail in targets closer to the boat....the trade-off for the 800kHz is that the SI image will be darker out to the sides of the images...

Here are 2 shots of the same structure with the only setting difference is frequency choice...

Notice the 455kHz is brighter out to the edge of the display...but fuzzier...
Notice the 800kHz is more detailed closer to the boat...but darker out to the sides...



Use the 455kHz for finding stuff all the way to the edges of the SI Range you have set....then set a waypoint on it...

Reposition the boat to rescan the waypoint with the 800kHz to see what it really looks like...

Rickie

[gotta_fish]

Thanks Rickie, Ive been playing around with my unit some , now im trying to fine tune it , how about the DI on it any advice on getting better pix with it .

[rnvinc]

DI (in the HB SI units)...seems to give better returns in the 455kHz...

Once again ...the 455kHz is going to be a little fuzzier...but it seems to show fish and structure echoes stronger...

Also we have to remember that the DI (in the HB SI units) is not actually using a "downward-pointing" piezo...(it's using the data from the 2 "side-pointing" piezoes...so we have to consider a different mindset in how to manipulate the conditions/ boat position to best work with this DI from SI technology...)

A dedicated DI unit uses a "downward-pointing" piezo...therefore our strongest echo returns are going to be directly straight down in the center of the fan shape beam....so we would get better images passing directly over structure...

DI from SI (in the HB SI units) uses the 2 "side-pointing" piezoes...therefore our strongest echo returns are going to be off to the side somewhat ...

1 learning tool I use in testing DI...(in my DI xducer experiments) is to drop a buoy to the side of a good brushpile and scan it several times from the same direction...but changing settings each pass...(frequency, DI width, Pallete color, DI enhance settings)...and also scan a little off to the side on some passes...

Rickie

[Don G]

Does any of the new HB HD/SI units have dedicated DI crystals? GeneC has a new 998 HDSI and that unit has the best DI I have ever seen.

[rnvinc]

Does any of the new HB HD/SI units have dedicated DI crystals? GeneC has a new 998 HDSI and that unit has the best DI I have ever seen.

None of the HB SI units use a "downward-pointing" imaging piezo...

All of the HB SI units have the piezo arrangement like the following X-ray...(2 long rectangular "side-pointing" imaging piezoes and 1 round disk "dual frequency" 2d piezo...)



Rickie

[kosmo]

Does any of the new HB HD/SI units have dedicated DI crystals? GeneC has a new 998 HDSI and that unit has the best DI I have ever seen.

don, some of these pictures can be deceiving because of the different conditions that can afect the sonar.the bottom line is that di/from si is what it is.sometimes a person can get some really great images if conditions are right but at other times not so great.in most cases, like rickie post above, the 455 khz will give the best results from the di from si.accually you can see why by just looking at rickies pictures above.thats a soft bottom in those two shots.see whats happenning close to the bottom in the 800 shot

[Don G]

I then assume that the dedicated DI units(958,etc) have 2D & dedicated DI crystals.

[rnvinc]

don, some of these pictures can be deceiving because of the different conditions that can afect the sonar.the bottom line is that di/from si is what it is.sometimes a person can get some really great images if conditions are right but at other times not so great.in most cases, like rickie post above, the 455 khz will give the best results from the di from si.accually you can see why by just looking at rickies pictures above.thats a soft bottom in those two shots.see whats happenning close to the bottom in the 800 shot

Kosmo's statement in blue above says it better than I ever can...

HB's "DI from SI" is what it is...

Rickie

[Don G]

Sorry, I just don't understand. Are you saying that the 958 has SI crystals that convert to DI? If so, why even come out with units like that.

Not complaining or bashing, just trying to understand