Weird interference: Horizontal, not vertical...

[Rico370v]

Whenever I have my trolling motor in the water I get a straight line on my sonar at 17ft of depth. I'm pulling my hair out trying to figure this one out! It's not typical interference that you would see such as vertical lines, it's horizontal, as if there was a fish or something at 17ft. just constantly sitting underneath the transducer mounted on the transom. Here's the setup:

1. Have changed out old MG TM to newer Xi5 MG, swapped out old Lowrance LMS-22c graph and ducer on the transom with new Elite Ti2 and 3n1 ducer on the transom. None of this has helped.

2. TM runs off two batteries on the port side bilge area with leads running up port side gunnels to the bow. Sonar and everything else including big motor run off starboard battery in the bilge. Sonar has it's own independent leads going straight back to the battery for power and for ground. Starboard battery shares ground with TM batteries (for easy jump starting.)

3. The Xi5 TM turns on as soon as you lift it to dunk it in the water. I verified today that it only does it when the unit is in the water. If I tilt it far enough to turn on but don't let it in the water, there is no issue. But as soon as it hits the water the anomaly appears on my sonar. Running the propeller or not has no effect; it's still there.

4. I'm new to downscan/sidescan etc., but it appears only on my 2d sonar, not my downscan at all nor sidescan. What could this be???

[acwd1950]

Prop wash from trolling motor? Troller inline with transducer on rear? Try raising or lowering trolling motor in water column to see if line moves? Remove ground between starboard battery and port side batteries? Onboard charger? Unhook onboard charger from cranking battery? Just a few suggestions to think about.

[Rico370v]

Some of these I've tried already, the rest I'll try tomorrow and report back.

[til]

Let me guess: your trolling motor is 17ft away from your transducer? What you see is not interference, it's an actual sonar return signal. I've heard this before but I'm not sure what causes it. Either the transducer is not mounted correctly or for some reason its sending signals far more horizontal than it should. If you look at actual measured transducer "cones" you will see they are not really cones at all, more a bit like christmas trees. Maybe its possible that by some irregularity in the production one of the top "branches of the tree" gets too long and reaches out to your trolling motor.

[Rico370v]

This has to be it! I raised the position of my transducer on the transom (adjusting for high-speed readings) and also raised the TM to half depth and it worked! The return signal is gone! I had no idea the ping would went out that far, but it all makes sense now. The return wasn't very strong; it was a solid line, but not bright yellow/red, just black. Glad to know I'm not going crazy!

[Jaak]

This has to be it! I raised the position of my transducer on the transom (adjusting for high-speed readings) and also raised the TM to half depth and it worked! The return signal is gone! I had no idea the ping would went out that far, but it all makes sense now. The return wasn't very strong; it was a solid line, but not bright yellow/red, just black. Glad to know I'm not going crazy!

Sidelobes.jpgEvery 2D transducer has sidelobes, every ducer has it little bit different. If we are speaking about ducers cone, this is very simplified. Sidelobe sees your trolling motor. Mine 83/200 sees TM, sees Livsight and Livescope ducers pole etc.