In the old days with points ignition and no computers, it didnt matter...

Today, there are some things NOT to do to prevent royally screw up a vehicles computer systems:

1. Dont exceed about 100 watts average, theres a new Standard that specifies that level. That only applies to Commercial or Ham because nobody would violate FCC rules and run a CB amp, would they? 🤣 I used a HF Ham radio in a Dodge truck rental and at 40 watts and above, the computers freaked out, engine lost power and cruise control didnt work. That was taking power from the battery and a correctly matched antenna.

2. Do not ' ground' the radios power cord to the body or with other ground wires, this can interfere with circuits or sensors. The radio should be powered from an approved accessory terminal or at the battery, provided that doesnt interfere with a battery sensor, and that the accessory feed can handle sufficient current.

3. Do not allow a DC current path from the radio out the coax to the body or chassis. That can interfere with sensors or circuits. Use a RF rated, Class 1 dielectric ( low loss) capacitor between the antenna end of the coax shield and antenna mount or vehicle body to prevent DC current from sneaking out the shield onto the body or chassis. About 1000 pF or more will do.

4. Dont mount the radio chassis so its in electrical contact with the vehicle. That will allow current across the chassis instead of the power cord.

5. Do not use a mismatched transmit antenna. When coax is mismatched, not only is the antenna system inefficient, but the coax loses shielding, and that risks coupling RF energy into other wiring. SWR should be as close to 1.1 as possible.

6. Mount the antenna as far from other wiring, and as high as possible from the vehicle. Tilting a vertical whip antenna is fine and can result in more directionality. Large body/ bed panels are good shields. Never route the coax close or parallel to other wiring.

FCC has strict limits on RF conducted/ radiated emissions from radio transceivers so if theres interference, dont go chasingvafter power filters or other gimmicks, its probably an installation or antenna problem, or, the vehicles electronics just cant deal with RF interference.

Video on my F250 install...

https://m.youtube.com/watch?v=q8SfERcsWkg

 

Good advice!!

 

Thanks! THis is "impossible to find" info from both the RF engineering and the "been there, done that" side.

Signed, Electro- RF R&D engineer (with a touch of automotive engineering background).