I added a down imaging depth finder to the front deck of my boat with the transducer mounted to the trolling motor. The D/F is powered by my cranking battery. I get all kinds of goofy depth readings and no bottom image when using the TM and it's very frustrating as I keep my eyes glued to that display when looking for underwater targets.  I never had this problem with 2D sonar.  The transducer is much bigger and I have a guard around it to prevent damage. I first thought it was due to turbulence but I'm thinking it may just be RFI from the motor itself.  I considered adding a  ferrite choke to the transducer cable, but don't know if I should install it close to the unit or transducer.  Any ideas what may be causing the problem, or suggestions on how to eliminate it.

I put my old 2D unit back on, but I'd really like to use the unit up front and not have to mount it on the dash?

If you have not already, run dedicated power directly from the cranking battery to be Graph.

 

ideally, there should be no reason why there is any connection between your trolling motor power system and your graph power system.

 

Thats where I would start. Ferrite rings and chokes are really just masks. If the charger is connected to both the trolling and cranking batteries then disconnect the charger it while out on the water to see if it changes the interference.

 

Let us know how it goes. Good lucks.

I have not had success with rings.  I have had good success with chokes put in the trolling motor power cables, so much that I just routinely do it every time I change trolling motors.

Mu unit is powered by my cranking battery which is charged by a different charger than the TM batteries. 

What is the difference between a ring and choke?

The kind that I have requires the plug wire to be cut and the choke installed in the line.  If my memory is correct it is the positive lead.  Mine come from a local shop in Springfield, MO.  I don’t know where they get them.  I have had success with them on both motor guide and minn kota trolling motors.

It's due to the wiring being too close to the power for the unit. I'm guessing if you step on the TM button, the interence starts and letting off stops it. Putting a ferrite choke around the transducer and power wire together closest to the unit where the TM wiring is will likely fix the issue . Common problem, no biggie. 

8 hours ago, iabass8 said:

 I'm guessing if you step on the TM button, the interence starts and letting off stops it. Putting a ferrite choke around the transducer and power wire together closest to the unit where the TM wiring is will likely fix the issue . Common problem, no biggie. 

This is exactly what's been happening. Never happened with my 2D unit, so I was puzzled as to why it was doing it with the DI unit. I didn't like switching from my DI on the dash to the 2D on the deck and now, hopefully, I won't have to deal with that.

Thanks for the help guys.

Does your power to your graph run on the same side of your boat as the power to your TM?