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Re: Inquiry



Roy Welch wrote:
> 
> Does anyone out there have a source of technical information
> regarding the precautions to be taken with mobile radio
> installations in auto Automatic Braking Systems and Air Bag
> deployment.  Specifically I am concerned with installing my
> 50 watt unit in a new Ford Motor product.  I would hate to
> push the mic button the first time and deploy the air bags!
> Some where I recall seeing some industry installation
> publications on the subject.
> 
> --
> 73, Roy

Hi Roy & Group,

I am experienced in a wide variety of mobile radio applications.  The
only publication I am aware of that specificly address' these issues
are some sent out by the car companies.  It was about RF interference
to the Anti-Lock Brake System.  In essence, these are the key points:

1. Route the positive and negative power cables directly to the battery.
   Use the appropriate good connection terminals and fuse both leads.
   Route the cables away from other wire harness'.  I also feel it is
   wise to avoid running the power cables near the cars computer, since
   these cables can carry RF energy.

2. Antenna placement should be where reasonable performance, good SWR,
   and minimal RF exposure to humans is acheived.  Use good RF
   connectors at the radio and antenna.  Watch for crimped RF cables.
   Remember that RF accesories such as duplexers, amplifiers, ect. can
   add more chance of bad RF connection and SWR trouble.  Check SWR with
   a reliable meter.

3. In addition, OSHA prohibits dash mount radios to be mounted over head
   such as from the roof.  The reason is that the radio could come loose
   in an accident and cause serious injury or death to the vehicle
   occupants.

4. Do not mount a mobile radio on or close to the covers of the air
   bag deployment area.  If in a crash, the air bag became deployed,
   the radio would be thrown toward the vehicle occupant. Ouch!

      These are principle common sense installation procedures.

I checked with Motorola Product Services to see if they were aware of
any other publications available on these issues.  They told me they
do not have anything else and have never had a RF caused Air Bag
deployment issue reported to them.

By far the most common RF interference related issue I have seen in 
newer vehicles is interference to the computer.  It is usually caused
by an unterminated accessory wires from the computer that act like 
antennas and feeds RF into the computer.  The most common symptom is 
the engine quits when the radio is keyed.  Also electronic instruments
go wacky (technical term?).  The worst band is low band where 1/4 wave
antennas are about 6 feet long, about the length one would expect of 
unterminated wires that would be used in an automobile.  UHF and VHF
bands typically cause little trouble except in high power (100+ watts)
and hi-SWR situations.

The automobile companies are very sensitive to issues that could cause
a health hazard.  You can see that it is in their best interest that 
they design systems that are resistant to interference.  Imagine the
disasters that could occur if you keyed your radio and your brakes 
locked or air bags deployed.  I suspect that by the time the air bag
systems were designed, the car companies knew to isolate them from
the operational computer system.  This would help prevent accidental
deployment in the event of computer malfunction or interference.

I hope this helps.  If you need more information, contact me directly
and I'll give you some phone numbers and Web sites where you can 
research this issue more throughly.

73, N8OCX
Brook Smith   n8ocx@amsat.org


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