Noise can be caused by a variety of sources, such as:
- Atmospheric noise
- Engine noise (from the ignition system or from the alternator)
- Any kind of electric motor
- Other electrical devices in the boat (navigation system, sonar device, power inverter, etc.)
- Local interference (from a nearby factory or business, etc.)
FIRST IDENTIFY THE TYPE OF NOISE
Turn off the motor and all other electrical devices. Be sure that all devices are really off. If necessary, turn off the "main disconnect" to kill power for the entire boat, then temporarily run power wires from the marine radio directly to the battery. Listen to the radio. If the noise sounds the same, then it is either atmospheric noise or local interference. Try changing your location to confirm whether it is from local interference. If there is less noise, then there is electrical noise coming from the boat.
WHAT TO DO
If the noise is coming from the boat, then it can be reduced or eliminated. Refer to the instructions later in this text.
If it is atmospheric noise, then there is nothing you can do. There will always be a certain amount of atmospheric noise, which can vary from day to day. It is not possible to filter atmospheric noise. To help maximize range:
-Use the longest antenna possible.
-Mount the antenna as high as possible.
Although these steps will not reduce atmospheric noise, they will help make received signals stronger so that they can be heard above the noise. When you are not receiving a signal, slowly turn up the squelch just until the noise stops.
ELIMINATING ELECTRICAL NOISE
First identify how the noise is entering the marine radio.
Disconnect the antenna cable from the radio and see if you still hear the noise.
If the noise stops, then the noise is entering through the antenna system. If you still hear the noise, then the noise is entering through the power wires.
NOISE ENTERING THROUGH POWER WIRES
Try another source of power. The cleanest source of power is directly from the battery. You may need to use shielded cable to prevent noise pickup from the ignition system. If you connect directly to the battery then it is recommended to use a 10 amp fuse right at the battery. This will protect the wiring. Try installing a noise filter on the power leads, as close as possible to the radio. Use a good quality filter rated 10 amps or higher.
NOISE ENTERING THROUGH ANTENNA SYSTEM
Unfortunately there are no filters available to filter noise that enters through the antenna. The best course of action is one of prevention – stop the noise from getting to the radio. The best options are:
Try moving the antenna cable around, to see if it affects noise pickup. If you notice a difference, then adjust the routing to minimize noise pickup. If possible, try relocating the antenna. Identify the source of the noise and filter the noise at the source so that it does not radiate into the marine radio (as described in the next section).
IF YOU ARE STILL HAVING TROUBLE
If the above recommendations are not helping, then it will be necessary to filter the noise at the source. You will need to identify the source of the noise and put a filter on the power leads of the offending device.
Start with all other devices in the boat turned off, then turn on each device one-at-a-time. When you hear the noise, you have found the offending device. Try installing a noise filter on the power leads to the device, as close as possible to the device. You could also try relocating the device. You might consider contacting the manufacturer of the device for recommendations.
If you only hear the noise when the engine is running, then it is either ignition noise, alternator noise, or electric fuel pump noise.
If the noise is a high-pitched whine that changes with engine speed, then it is the alternator. A filter on the alternator would be the solution. If the noise is a high-pitched whine that does not change with engine speed, then it is most likely an electric fuel pump (if your boat has an electric fuel pump). Placing filters on the power leads to the fuel pump should help. If it is a low-pitched rumble that changes with engine speed, then the noise is coming from the ignition system. Try replacing the spark plug wires with good-quality noise suppression wires. You can also contact the engine manufacturer for recommendations.