7e.1 Understand that EMC problems in motor vehicles can have serious safety implications and identify suitable precautions.
The main problem with the
installation of amateur radio installations in modern motor vehicles is the
risk of pick up by the electronic management system of the car which
could lead to damage to the electronics and a consequent loss of
control and high cost of repair.
Some precautions from an EMC point of view include:
- Ensure
the antenna is well secured to the vehicle, The centre of the roof is
often the best place from a transmitting point of view, but the thin
metal may not be mechanically strong enough to support an HF antenna. It
may also be difficult to bond
the mount to the car chassis as the roof lining is difficult to remove
in some cars. This is important to prevent unwanted currents circulating
through the bodywork.
- Mounting the antenna at the back of the roof, well away from the engine can help to reduce EMC problems inside the car.
- Connect the power cables directly to the battery using the thickest cable possible.
- Fit a fuse ( protected from water) to the positive and negative leads of the battery
- Earth the negative cable at the TX/RX to the chassis.
- Motors in cars
can create interference (wiper motors, starter motors) First of all
make sure the motor is well earthed to the chassis. If this does not
cure the noise, try adding capacitors between the positive and negative power line and the
chassis 1uF for HF.
- Place
an inductor in the positive and negative leads to the motor. The value
of this should be about 30uH and built to handle the current ( > 7
Amps)
Other safety precautions include:
- Use a radio that has its controls in an easily accessible position, without the need to enter sub-menus.
- Position the radio where it is easy to see and does not obstruct the view of the road.
- Position the radio where it is not on top of an airbag.
- Ensure adequate ventilation
- Where possible use a head set for hands -free operation.
- Be careful when drilling holes not to damage important parts such as fuel lines.
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