Externally Generated Electronic Interference Guide to Radio Installation
The following general guidelines are for installing radio-telephone or two-way communications radios, land-mobile radio, in a vehicle supplement. These guidelines DO NOT replace detailed instructions provided by the radio equipment manufacturer. Detailed
installation instructions are the sole responsibility of the radio equipment manufacturer.
Experience has shown that most electromagnetic interference (EMI)/radio frequency interference (RFI) concerns can be prevented or eliminated by following the guidelines. If EMI/RFI concerns persist after following the guidelines, and after
ensuring the installation conforms to the guidelines, contact the vehicle and radio equipment manufacturer for additional installation or equipment operation instructions.
Transmitter Installation
| • | Install remote radio transmitters as far away from other electronic devices and as near to the side of the vehicle body as possible. |
| • | Mount transceivers, transmitter and receiver in one box, under the dash so as not to interfere with vehicle controls or passenger movement. |
Antenna Installation
Each vehicle and body style react differently to radio frequency energy. When dealing with an unfamiliar vehicle, test various antenna locations by using a magnetic mount antenna and checking for adverse effects. Antenna location is a major factor in EMI/RFI
concerns.
Antenna Cable Routing
| • | Use high quality, 95 percent shield coverage, coaxial, coax, cable. Route the coax away from any electronic components. |
| • | Route antenna cables as far away from vehicle wiring as possible in order to reduce the likelihood of the vehicle wiring acting as an antenna for interference. |
Radio Wiring and Connector Location
| • | Connect transmitter power leads directly to the battery. |
| • | For transceivers, transmitter and receiver in one box, with ignition control, place a 12 volt power contactor at the vehicle battery. Drive the contactor coil through an appropriate inline fuse, from an ignition circuit not powered during
engine cranking. |
| • | Any negative lead from a handset or control unit must return to battery negative. |
| • | Connect the positive lead from a handset or control unit directly to battery. |
| • | Fuse handset or control unit positive and negative leads separately from the transceiver negative and positive leads. Use correctly rated fuses. |
Power and Ground Wire Routing
Route radio power and ground wires as far away as possible from electronic control modules.
Troubleshooting
The following are common causes of EMI/RFI concerns:
| • | Power leads connected to points other than the battery |
| • | Improper antenna location |
| • | Poor shielding or connections to antenna cable |
| • | Transmitter or transceiver wiring too close to vehicle electronics |
Externally Generated Electronic Interference Speed Sensor Signals
Use the following procedures in order to determine if speed sensor signals, generated by a source external to the transmission or wiring harness, are present:
- Turn the ignition ON.
- Keep the engine OFF.
- If the transmission control module (TCM) is ON, install the scan tool.
Important: If false speed signals were present at the previous shutdown, the TCM might still be ON, even though the ignition is OFF. The scan tool is powered by ignition power. The ignition must be ON in order to use the scan tool
to read the speed signals.
- Read the speed sensor signals.
- If a speed sensor signal is something other than one (1), there is a short to another circuit that is carrying an AC or pulse width modulated (PWM) signal.
- Measure the resistance of the sensor.
- Inspect for shorts to other circuits within the harness or transmission connector.
- Inspect to ensure there is no conductive material inside the connector.
- Inspect to ensure the speed sensor circuit wires are a twisted pair.
- Inspect to ensure a properly grounded drain wire.
- Inspect for the presence of a strong external AC signal.
- Repair or replace parts as required.
