Engine noise interfering with FM radio

[Tom Pawlik]

I just put the boat I bought last fall in the water. The previous owner had a stereo shop install the stereo system. It is an Alpine am/fm/cd unit connected to a 400W amplifier with 4 boston accoustic speakers. It has a postive and negative Monster Wire connected to the starting battery. I had been listening to the stereo while getting the boat ready for the water and it works great. But, when the engine is running I am getting huge interference with the radio in all modes. There are two batteries running thru a selector switch. Should the stereo be connected to the battery that does not start the engine? Would that eliminate the engine interference? Something is not right. I cannot imagine the previous owner tolerating this noise.

[Bullshipper]

Spark plugs with resistors will help.

[76GMC1500]

and resistor wires.

[capehaze]

The replies are good advice if you have ignition noise - fast clicking/popping whose rate tracks engine rpm. Another source can be alternator "whine", a whistle that changes pitch with rpm. The whine can come from bad alternator diodes or a somewhat "soft" battery. Filters for the power feed to the stereo can sometimes help. The must be rated for your peak currents (high with your system) and of good quality to work well.

In any event it is best to not have the system on the start battery.

Woody

[Glen E]

check the ground wire on the radio.....

[Montauk Local]

Glen E - 5/11/2008 8:56 PM

check the ground wire on the radio.....

Exactly. Particularly the lugs where the wire is bolted to the ground of the boat. Could be the connection loosened by vibration.

Also dis-similar metals when joined along with salt environment will produce electrolysis. that will definitely effect your ground connection.

Take the connections apart and wire brush or sand them off good then get some silicon dielectric grease, grease up the lugs, etc. good and reconnect.

Use stainless lock washers or stop nuts if you can.

[Tom Pawlik]

Thanks guys, I was pretty sure the whining noise was the alternator since it changed pitch with the speed of the engine. I will check all the grounds and move the amp ground and power wire to the #2 battery and apply the dialectric grease. If that doesn't work, I will buy a filter. Crutchfield and others have them for about $20.00

[XV2PS]

Install this on the power cords of your radio (as close to the radio as possible), it will block the noise for some bucks:

[capehaze]

Hi Pierre,

Good filters use your schematic. Just thought I would mention to the group that the torroids and wire gauge must be sized appropriately to handle the high currents of a 400 watt, 12 volt amplifier. BTW, Visited your QRZ page - Quite a life!
Ham homebrew, boating, and fishing: albe24.com
Woody, KZ4AK

[XV2PS]

Hi Woody,

You are right. I cannot find the picture of the one I did.

Saw your webpage. Man what a good mess your shack :-)