Thread: Interference...

Originally Posted by shortdraw

The front in it is on 455 kHz console is mega at 1175 I think..power wires for f2f are on opposite side of boat from trolling motor...will try to run wire between negative on batteries. Do have a on board charger never thought of that being a issue...

Separating wires is a good practice. Are there any other wiring in the side of TM wiring? DC motor commutation creates RF, which creates the undesirable common mode interference. Air is a dielectric. RF can be coupled into adjacent wiring. If you have some spare wiring, you can wire to the TM bypassing your existing run ( lay it in the boat) and see if this reduces the noise. Try this if nothing simple works. Leave the wire to the TM housing in place.

Twisted wires is also a good practice for longitudinal balance. AG Bell discovered twisted wire applications in late 1800's. If it weren't for twisted wires, we could not talk (hear) via phone line, nor could we send/receive hi speed data. History lesson or a refresh on recall? Your call.

Another question??? Is the noise present when you steer or when you power the motor? Or both? That little steering motor is a big big source of RF.

I had similar issues with my trolling motor and sonar. I tried everything mentioned here and then added ferrite core filters on both positive and ground on both units and that solved all issues. The wires don't just pass thru the filters but pass thru and then thru the filter again causing a loop in the wire thru the filter. This was a last effort after everything else failed but it worked. Even made my am radio work properly. I suppose having a well grounded boat is comforting . My problem was specific to only the upper frequencies associated with the down view functions of sonar.

Your AM radio was telling you that there was RF in the air. An am radio, tuned to lower band frequencies and turned to an "off or between active broadcast frequencies" can be use like a Geiger counter to find rf sources.

Thanks for all the info..I'll try them and see if I can't fix the issue. It's not horrible but still would like it to be clear all the time.

I realize that an AM radio was designed to pick up spark plugs firing in German airplanes during WW1 but the one in my boat still picked up the motor noise from my trolling motor, live well pump, and sonar. The live well pump and trolling motor caused drastic interference on the sonar. While I did not put the filters on so that I could listen to the radio still yet a side effect of the filters was that it cleaned up the radio. The initial design of the superheterodyne receiver in 1918 by US Army Major Edwin Armstrong is the father of all AM radios which is why an AM radio will pick up all RF in the area and transmit them thru the radio speakers. A test question I still remember from one of my earlier electronics courses. While I had my boat electronics grounded 7 ways from Sunday I still had interference in the 800 Hz range on my sonar as a last ditch effort I decided to place a few ferrite core filters in line with power and grounding on the offending components and my interference problems were solved.

Where can a guy get these ferrite core filters at?