Fish Finder Interference

[jhib]

I have a Humminbird 535 (I think). It works just fine when my main engine is off, however, when the engine is running I get false signals as to a lot of fish symbols and lines on the screen. It is obviously engine noise. My question...what is causing it and how do I correct it so I can use the fish finder while I'm running the boat. PS: It is really bad at WOT. Thanks in advance for any help. Jim

 

[ajgraz]

Re: Fish Finder Interference

Are you sure it's not water turbulence at the transducer when running (rather than some sort of electrical interference)?

 

[jbetzelb]

Re: Fish Finder Interference

Are you sure it's not water turbulence at the transducer when running (rather than some sort of electrical interference)?

This would be my first guess. You might try connecting the power to the fish finder directly to the battery and see if it gets better. Doing this should reduce interference you would get if your connected to the boats elertrical system. Does it have the problem with the engine running but in neutral? If it does it would help prove it isn't turbulence.

 

[jhib]

Re: Fish Finder Interference

Thank you for the reply. No, I'm not sure if it's turbulence. Someone else suggested that I connect directly to the battery. If it goes away, it is electrical. If it doesn't, it must be turbulence. Thanks again. Jim

 

[dingbat]

Re: Fish Finder Interference

Connecting directly to the battery will not prove or disprove anything. The transducer cable could be the source of the interface.

Turbulence and engine noise is very easy to diagnose. If revving your motor while at drift or on the trailer causes interference, its engine noise. If the interference only occurs at speed, it’s turbulence.

 

[MH Hawker]

Re: Fish Finder Interference

resistor plugs may help.

 

[bruceb58]

Re: Fish Finder Interference

Connecting directly to the battery will not prove or disprove anything.

It rules out the power side as the source of the noise right?

I agree with you that running the transducer cable next to any other electrical wiring could also be the culprit. I always run mine as far away from wiring as possible.

 

[ameee]

Re: Fish Finder Interference

jhib

With Humminbird and I am sure others may have the same issue. First if it is engine is when you are out on the water, go to neutral and rev it a little bit (do not over rev) and see if is affecting the screen.

Most of the time the interference is electrical noise and it can come from the power source and sometimes the routing of the transducer as dingbat stated.

What you may want to do, depending on how much trouble it is, take the power source, run a set of temp wires across the deck away from everything and connect directly to the battery. Then likewise take the transducer wire again across the deck away from everything and connect to your bird. If the issue goes away it is one or both of them combined. If it is electrical coming from the engine you can purchase and install chokes on the positive wire.

I have had very little noise when running the big motor, the trolling motor has caused a lot of noise.

George

 

[dingbat]

Re: Fish Finder Interference

It rules out the power side as the source of the noise right?

Only if you disconnect everything else from the battery and run the ground directly to the battery as well. Leaving a failing rectifier or a faulty ignition circuit connected to the battery will prove nothing. It also wouldn't discount a feedback off the ground.

You’re not going to pick up much of anything on a transducer unless the cable is unshielded or run in close proximity to AC.

 

[bruceb58]

Re: Fish Finder Interference

Only if you disconnect everything else from the battery and run the ground directly to the battery as well.

I see what you meant now. Yes, the test would be to run it to a seperate battery which would only power up the finder.

 

[Jlawsen]

Re: Fish Finder Interference

What side of the motor is the transducer mounted on and how far away is it from engine. The transducer and the cable are shielded and unless someone cut it and didn't terminate the shield it should not be succeptable to electrical interference. Prop noise is probably what you're seeing. I have side scan on my right and my standard transducer on the left. It's not supposed to be mounted on the left and I get noise on it just like the manual said I would. The side scan is clear as a bell.

 

[UncleWillie]

Re: Fish Finder Interference

If it goes away with the engine running but not moving it is turbulence.

If it goes away when operating on a completely separate isolated battery it is electrical interference in the wiring.
Alternator or Ignition noise.

If it remains when operating on a completely separate isolated battery it is RF interference through the air.
More likely the ignition but also possibly the Alternator.