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Re: [RFI] HF Mobile Installation in 2001 Mazda

To: "RFI List" <rfi@contesting.com>
Subject: Re: [RFI] HF Mobile Installation in 2001 Mazda
From: "Jim Brown" <jim@audiosystemsgroup.com>
Reply-to: Jim Brown <jim@audiosystemsgroup.com>
Date: Fri, 04 Feb 2005 13:06:11 -0600
List-post: <mailto:rfi@contesting.com>
On Fri, 04 Feb 2005 10:30:31 -0800, digital-conjurers@adelphia.net 
wrote:

>Will the radiated RF power at this HF frequency, in the config
>above, have the potential to fry any of the on-board computers 
>or electronics in the vehicle?  

Unlikely if you follow good engineering practice.

1) Get your power directly from the battery ( both positive and 
negative). 

2) Run coax with good copper braid to the antenna, bond the braid 
to the car body at the antenna, AND -- VERY IMPORTANT -- MAKE SURE 
THE CAR BODY AT THE ANTENNA IS BONDED TO THE REST OF THE CAR BODY. 
This will also maximize the radiation efficiency of the antenna 
and minimize the receive noise. 

#2 is not trivial. I use a license plate mount to put a Ham Stick 
on my Volvo S80. The license plate screws are insulated, so that 
requires a copper bond between the mount and the trunk lid metal. 
BUT -- the trunk lid isn't bonded to the car body, so that 
requires ANOTHER copper bond between the trunk lid and the car 
body (around the hinges).  

3) K9IKZ has observed that it is also helpful to bond the tailpipe 
to the car body at both ends to minimize receive noise. I would 
also expect this to minimize RF getting into the computers. My 
Volvo is fairly quiet (but not dead quiet), and I haven't gotten 
around to doing this yet. 

FWIW, I run 100 watts in my Volvo, which is also loaded with 
microprocessors, and have never had a sign of RFI to the car. Of 
course, it's a European car, and Europeans are generally more 
sensitive to EMI, thanks to the EU's EMC directive. 

Also FWIW, others have made a big point of bonding the radio to 
the car body via its mount. My FT100D (yeah, I know, not a great 
receiver) sits on the hump between me and the passenger seat. I'm 
lazy about installs, and I mostly use in in the shack on our 
club's FM repeater. If you've done #1 and #2 right, it doesn't 
matter. 

Jim Brown  K9YC


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