When you’re out on the water scanning with your down image you have the options of using the 455 kHz or 800 kHz setting on my Humminbird Onix. In the photos I’ll show you what you are missing if you are not using the correct setting. When you are in deep water you need different setting than when you are in shallow water. With the Humminbird Onix the 455 kHz setting is using two 86 kHz beams at once which covers 172 degrees. While the 800 kHz setting use two 55 degree beams that only cover 110 degrees total. So you can see that the narrower beam does not reach out as far as the wider 455 kHz setting.
With the 2D or sonar beam you have a choice of either the 20 degree or the 83 degree cone or a combination of both. You need to remember that with the 2D sonar cone set to 20 degrees you are only scanning 1/3 the depth of the water. In other words if you are in say 9 feet of water you are only looking at a 3 foot circle under your boat. With the 83 degree setting you are covering an equal area to your depth. If you are still in the 9 foot of water you are scanning a 9 foot circle under your boat. For the best scanning I’d suggest you a combination of both the 20 cone and the 83 degree cone.
Now let’s look at the photos a second. The photo above I have the setting set to 455 kHz with a wide beam selected. In this can I am in water that is less than 10 feet deep and you can see I can scan a very wide area out from my boat.
Now in this photo I have my unit set to 800 kHz with a beam wide setting which only covers 110 degrees out from both sides of the boat. I’m still in about 10 feet of water or less. As you can see you can’t see nearly as much detail as in the photo above set to 455 kHz.
Now let’s look at the down image scan while I’m scanning in water around 30 feet deep in the photo above. I have the unit set to 455 kHz and I’m covering 172 degrees under the boat. The fish by the way are stripe and shad. As you can see there are rocks close to the shore line.
Finally in the above photo I have the unit set to 800 kHz in 30 feet of water and scanning the exact same water and since I have a narrow 110 degree of coverage I can’t see the shoreline or the rocks near the shore. I can still see the stripe and the shad but in this case the 455 kHz gave me more detail than the 800 kHz setting.
Let’s wrap it up, the setting are really up to you and what depth water you are in. If you only have a Down Image unit the beams are different in that your choices are 455 kHz using a 75 degree cone angle and 800 kHz which only gives you a 45 degree cone angle which will not give you as much coverage as the side Image units. One recommendation I suggest is to set the Down Image to 800 kHz and the Side Image to 455 kHz while scanning so you don’t get the cross-talk if the transducer trying to pick them both up at once id you have them set to the same 455 or 800 kHz setting.
Hope this helps you better understand your unit better….