Interference

[FordsnFishin]

While running the trolling motor I'm finding that it interferes with the sonar screen. (Random lines, screen gets darker). 

 

Trolling motor is is 24v dedicated. Sonar is on it's own dedicated battery.

 

Thoughts on why it is happening and ways to fix? Thanks

[12poundbass]

Maybe your transducer isn't the right one for a trolling motor? I know some transducers made for trolling motors have more shielding to protect from RFI from the trolling motor.

[FordsnFishin]

I should mention the transducer is mounted on the back of the boat... Not even to the trolling motor itself.

[eddallen]

Can you post a pic of the screen during the interference?

It's possible that the TM is creating air bubbles that travel along the hull and over the face of the transducer...possible.

You can check this while underway using the TM and looking astern at the transducer.

[FordsnFishin]

I'll get a photo of it. 

 

Although I don't think this is the case as I could be sitting still and as soon as the trolling motor is initiated you will see the interruption and as soon as it's off it goes back to normal.

[eddallen]

1 hour ago, FordsnFishin said:

I'll get a photo of it. 

 

Although I don't think this is the case as I could be sitting still and as soon as the trolling motor is initiated you will see the interruption and as soon as it's off it goes back to normal.

OK so that is definitely electronic noise and sometimes these gremlins can be hard to tackle. Where are the TM batteries located?

Where is the MFD located, console or bow? 

[FordsnFishin]

Batteries are located in the very back of the boat, trolling motor upfront.

 

The sonar screens are synced together and it comes across on both when I use the trolling motor. Monitors are upfront on a ram mount about a foot away from the TM, other is at console.

Should mention the TM power wires are ran on opposite side of all the electronics.

[12poundbass]

Could it be a grounding issue? I have no clue just thinking outloud.

[Scott F]

If you have dual frequencies available on the depth finder, try the other one. It worked for me.  

[FordsnFishin]

5 hours ago, Scott F said:

If you have dual frequencies available on the depth finder, try the other one. It worked for me.  

Are you saying to use different frequency on each sonar?

[Scott F]

Yes.

[slonezp]

What brand units? 

[FordsnFishin]

On 7/20/2017 at 6:23 PM, slonezp said:

What brand units? 

Lowrance

[iabass8]

Unplug one unit and see if the problem stays. Do the same with the other. If the problem isn't there /w just one unit on, switch the front unit to 83 and bow to 200 or vise versa. 

[slonezp]

5 minutes ago, iabass8 said:

Unplug one unit and see if the problem stays. Do the same with the other. If the problem isn't there /w just one unit on, switch the front unit to 83 and bow to 200 or vise versa. 

This brings up a good point. That would determine if in fact it is interference or crosstalk. On my 20ft boat, crosstalk starts between the bow and transom in around 18-19fow. The interference is caused when my trolling motor is on anything but full speed.

What I have done to reduce interference is install a ferrite ring on each graph that I got from Humminbird and a second freeite choke I bought at radio shack.  

http://kf7p.com/KF7P/Ferrite_chokes.html