Reduction of radio noise interference to a level that permits normal operation of electronic devices depends on several factors. First, how sensitive the electronic device is to the interference, and then how strong is the interference.
It is important to be able to identify the source of interference noise so suppression can be applied systematically.
Ignition noise will sound, on a radio receiver, as a "tick tick tick" at engine idle RPM, and will sound like a buzzing noise as the RPM of the engine is increased. Ignition noise may be radiated from the ignition coil, spark wires, ignition leads, tachometer lead, and instrument cables.
Alternator noise will have a "whining" sound much like a siren as engine RPM is changed.
Switches turned on and off will produce a "tick" sound, this sound can be tolerated unless the switch is used continuously.
Good practice in the installation of electronic devices may solve the interference problem. The manufacturers instructions must be followed carefully. The three procedures below should be followed also.
1. Take power directly from the battery with a properly fused separate circuit.
2. Install all electronic equipment and its wiring as far as practical from all engine and engine control wiring.
3. Install radio antenna and antenna lead as far as practical from the engine, engine instruments and the engine instrument wiring. Do not attempt to add shielding to the antenna lead. Use wire recommended or furnished by the manufacturer.
Boat Electrical System
A loose connection in any circuit can result in very annoying radio noise or impulses affecting proper function of most electronic gear.
1. Use properly installed terminals, corrosion proof fasteners, lock washers on screws and under nuts for good connections.
2. All terminals should grip the wire insulation as well as the conductor and should be soldered.
3. Wires and wire harness assemblies must be properly supported so their weight is not pulling or hanging on the terminals.
4. Maintenance should include checking all connections occasionally since boat and engine vibration and corrosion can loosen connections.
5. Connections exposed to the elements like battery, fuse, terminal and quick-crimp connectors should be lubricated with grease or protective spray designed for this purpose.
Shielding Electric Motors
Motors for pumps (A), blowers, water systems, etc. will have a constant "whine" and can be identified by turning them on one at a time.
1. In most of these motors, a .5 MFD bypass capacitor P/N 378491 (B) between the positive lead (C) and ground may help quiet the noise.
2. Tape the connection to protect from moisture.
3. Starter motors, like switches, can usually be tolerated since they are operated for a very short time.