Thread: 455khz or 800 for the si

The 800kHz generally will give clearer images....(sorry 797,798 owners-you don't have this option...)
The 455kHz generally will be advantageous in deeper water...
This effect can clearly be seen by switching between the 2 and noticing that for any given SI sensitivity setting the 455kHz beam will be brighter (but fuzzier) than the 800kHz beam...

SI sensitivity settings for either beam will be dictated more by water conditions and/or bottom composition...
a. Dingy algae filled water will absorb more sonar than clear water....therefore needing a higher setting...
b. Deeper water will absorb more sonar...therefore needing a higher setting...
c. Mud bottom will absorb more sonar than a hard bottom...therefore needing a higher setting...
"anytime there is a condition that absorbs part of the sonar sound wave...that leaves less sonar sound wave data to be reflected back to the unit for display"

I keep my 1197 on 800kHz most of the time to get the clearer images...
But there are times in deeper dirty water with a mud bottom that the 800kHz just "will not" reflect enough sonar to get an acceptable (bright enough) image....this rare occassion will lead me to use the 455kHz beam and adjust the SI sensitivity down to an acceptable brightness...

I keep the contrast on about 10-12...
Sharpness off unless I want to see the fish better (raising the sharpness will make the fish more visable but also makes the image more "grainy" looking)...

I keep the "SI Enhance" window up on my screen anytime I am viewing SI...

This gives the abilitiy to change "SI Sensitivity" setting without (opaquing out) any other split view that I have up at the time...

I use the SI Sensitivity setting as a "brightness" control for my SI image (as different water conditions/bottom compositions will make the image brighter/darker..)

SI Sensitivity up will brighten the image...
SI Sensitivity down will darken the image...

I frequently change this SI Sensitivity setting as my SI image changes in brightness...

Here is a screenshot of the "SI Enhance" window overlayed onto the SI image... I had to adjust the sensitivity to 19 to get this mud bottom to reflect enough sonar echo to get an acceptable image...



Rickie