[Amps] Amps Digest, Vol 172, Issue 34, topic 1

[Jim Brown]

On Thu,4/20/2017 9:00 AM, Gary Smith via Amps wrote:
> A few years back we had a 2011 Toyota Prius. When I decided to install 
> a vhf/uhf rig, I contacted Toyota with concerns about the on-board 
> computer.

VHF/UHF in a vehicle is FAR less likely to cause problems with 
automotive electronics that HF. Two very important reasons. First, power 
levels are generally a LOT lower. Few rigs put out more than 50 W, and 
the largest commonly available power amps put out about 160W on 2M and 
100W on 440 MHz.

Second, at HF, all the metal in the vehicle serves as the counterpoise 
for the vertical part of the antenna, but connections between that metal 
is often poorly bonded or not bonded at all, insulated by paint. The 
result can be lots of RF current flowing in metal parts in close 
proximity to vehicle wiring. That current can couple quite strongly into 
that wiring, especially if it is not twisted pair. And, taking 
wavelength into account, RF current maxima are much more likely to be 
confined to the reoof of the vehicle, as compared to HF where they are 
next to sensitive wiring.
>
> What I received was a nice two page letter on where to run the power 
> and control cabling. Their general instructions was to run the cabling 
> in the trough to the right of the passenger footwell in the right side 
> of the car so to keep the rf away from the ob computer/controller.

This makes no sense. Unless something is very wrong with the radio, 
there should be no RF on power or control wiring. From an EMC point of 
view, the ANTENNA and it's counterpoise (metallic parts of the vehicle) 
are the source of RF, NOT the radio. Clearly, whoever at Toyota wrote 
this doesn't have a clue.

73, Jim K9YC