Introduction to Radio Noise Suppression



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.


Initial Installation

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.


   Install Resistor Type Spark Plugs

The following suggestions, followed in order, will achieve adequate radio noise suppression with minimum effort.
Install resistor type spark plugs on all cylinders for radio noise suppression.


Standard Plug       Use       Suppression Plug
==============================================
545                use        RJ4J
565                use        R56J
L45                use        RLU
L7J                use        RL75
L86                use        RL86
L78V               use        QL78V
L81Y               use        QL81Y
L7754              use        QL7754
UL77V              use        QUL77V
UL815              use        RL82
-------------------------------------------------------------
   Installing Separate Battery, Filter or Suppressor

1. Connect electronic device (D) to a separate battery (E). This bypasses interference from all sources that may be conducted through the engine's wiring or charging  circuit. If satisfied with these results, either use    separate battery or add filter. The filters should be close to the equipment.

2. Current draw of the electronic device dictates whether a filter or a suppressor should be used. The filter or suppressor should be located close to the electronic device.

3. When the current draw of the electronic device is 4 amps or less, add a radio line filter (F) made as shown using a suppressor (G) with 225 turns of #16 gauge wire soldered to an electrolytic capacitor (H) (1000 MFD,25 WVCD)

(a) Inline S.F.E. 4 amp fuse
(b) Red + lead
(c) Black -
(d) Solder & tape securely

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