Another inteference question?

[Jbass2]

Humminbird 959. I used to have it hooked up through the factory fuse bus at the bow. I always had a little interference, but I just dealt with it. I recently installed a livescope system on a dedicated lithium battery that is not hooked up to anything on the boat. I ran a power cable from the battery to the bow and put in a new fuse bus. I thought that by hooking the 959 up to this bus (thus removing it from the cranking/trolling batteries) that all the interference would be removed. The bus only thing hooked up to the bus is the 959 and a garmin 93 echo.

Boy was I wrong. The picture is fine until I hit the trolling motor. Now the interference is so bad the picture is useless.
I don't get why the humminbird is getting interference from the trolling motor when it is hooked up to an entirely different electrical system. All the cables in the bow compartment have been moved around because of the installation of a new unit, but I don't see how that could create the amount of interference i now have.

Any ideas?

[Wayne P.]

Where is the 959's transducer?

[Jbass2]

It is on the foot of the trolling motor.

[Wayne P.]

The source for RFI did not change so the RFI path for it is the transducer, cable and power wiring. Any added filtering benefit on the power side from the other circuit was eliminated and you now get the RFI more directly.
PLUS the Livescope cable/power wiring is an additional antenna for the same RFI frequency your 959 uses.

[Jbass2]

Is there a simple way to get rid of it? I don't see how I can separate all the cables. Does the RFI come from the bottom of the trolling motor?

[Hollada]

Things to try, one at a time to see what works:
- Ferrite torroid mix 77 - wrap your transducer cable through it as many times as possible. Get the biggest inside diameter toroid you can find
- run a ground wire from your TM skeg to your cranking battery neg.
- have your brushes checked in your TM to see if they are getting worn
- ensure you’re TM powerlines are as far as possible from your graph power and transducer lines
- if you have a network, try disconnecting that from the unit and see if it impacts the noise. If it does you can try a toroid on your Ethernet line and /or grounding your hub
- some have claimed success wrapping a piece of inner tube around the TM under the ducer mounting bracket

Good luck chasing this down. Interference is a PiTA!

[Crestliner16]

That's about as complete of a laundry listas your gonna get. I am lucky that I only needed one small rfi choke. I should have stocked up on that kind of stuff from Radio Shack. Good luck.