vhf makes noise with fish finder

[dsujen]

I have a center console 18 ft cobia. All my electronics are the same as last year except I installed all new wiring and a 3 foot center console antenna on the helm. It used to have the big antenna on the gunwale for the vhf. Everything works great by itself. If I have the vhf on, it's fine. If I have the stereo on, it's also fine. Fish finder, same thing. But when I use the fish finder and vhf at the same time, I get a non stop cb chugging noise every second. As soon as I shut off the fish finder the noise goes away. What can I do? Is my wiring job too neat cause before they were just hanging out. Now I have them wire tied together sort of like a home made harness. Do I need to buy a filter of some sort like for car audio system problems?

 

[KingsPoint]

Re: vhf makes noise with fish finder

First thing to do is to determine whether this is power noise or RF noise. This is easy to test. Just unplug the antenna from the VHF. If the noise on the VHF goes away, you know that it is coming in through the antenna line somewhere. Trace the antenna coax, making sure that it is not bundled with any other DC or transducer lines. You said that this started when you bundled the wires together, so this may be the problem.<br /><br />If the noise continues without the antenna connected, the noise is coming from the DC power lines. A VHF radio (or any radio, for that matter) should have it's own dedicated circuit. For example, don't wire it to the same breaker as any other piece of equipment. Try to isolate the VHF power lines away from the everything else. A noise filter can help, but a properly setup radio should not be too difficult to get noise-free.

 

[Gone]

Re: vhf makes noise with fish finder

And don't ignore the ground circuit. A common ground is like a party line spreading noise to everything connected to it if the ground is marginal with small wiring.<br />Ground the VHF and the depth sounder to the battery with SEPARATE wires. Make sure that the old grounds are disconnected so that the only grounds in play are the new lines to the battery. Even one left connected contaminates the whole system and will leave your work as wasted effort.

 

[limacina]

Re: vhf makes noise with fish finder

I did some acoustics sensor work at one point and we had to keep all of the signal wires at least 4" from dc wires and when they had to cross, we made sure they were perpendicular (90 Degrees) to each other. Never lay the cables along side each other.<br />This could probably be common sense for VHF antenna cables too.

 

[waterinthefuel]

Re: vhf makes noise with fish finder

I have the same problem, sometimes I hear noise whether or not my fishfinder is on, but it's not on a dedicated circuit.<br /><br />Ahh, something to ponder.