Terrova and Helix 12 DI Interference

[Pbix]

Yes, yet another post on interference...

I've spent alot of time trying to research this issue in my Helix 12 DI with a Terrova. My set up.

Helix 12 DI bow mount, external DI transducer on TM, US2 disconnected. Powered by the cranking battery (new). Only the engine and power bus bar on the boat are powered by this battery.
Terrova 24V ipilot link bow mount.
Interference in DI and Sonar when trolling motor is on anything but 10.

So, I've tried all of these, that didn't work:
Seperated all power wires and transducer cables...man was that a pain (didn't help one bit)
Checked the fuse in the TM head, it was good, replaced with a new one just in case.
Called HB, already had one ferrite in the head, added another to the other pair of red/black wires.
Ground wire between trolling motor negative and the cranking battery
Ground wire from base of trolling motor mount to boat.
Ground wire from power bar buss to boat
Ground wire from power bar buss to TM battery
Ground wire from power bar buss to cranking battery
Ground wire from NEG of TM plug to boat, TM battery, or Cranking battery
Wrapped heavy duty aluminum foil twice around any remaining nearby transducer cables
Grounded the neg input into the TM control board to the TM batter, cranking battery and boat itself



Here's what helped:
Ground from TM battery to boat itself...about a 75% reduction in noise...couldn't figure out how to reduce the rest.

So, finally....I bought the TMC-1 in-line choke.
Actually brought back the original level of interference...WTH?
But on whim, I ran a ground wire from the negative wire on the "output" side of the TMC-1 choke...magic..99% interference gone

So, why in the heck would grounding the TMC-1 between the choke and the TM control board work....what is going on?

[sfw1960]

Inductive Reactance is a very strange critter - it makes electronic noise crawl around the darnedest places, or not....

Super unpredictable, as you have discovered.

Nice job on taming that crud!

[cody161]

When you say you grounded the TM battery to the boat, what did you actually ground it to on the boat?

[Pbix]

I found an aluminum brace under there that was welded to the hull and screwed in there.

[Bob B]

Well .... That answer took a while.