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Re: [RFI] FW: Iginition Noise [Incident: 100111-000562]

To: "rfi@contesting.com" <rfi@contesting.com>
Subject: Re: [RFI] FW: Iginition Noise [Incident: 100111-000562]
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Mon, 11 Jan 2010 13:40:39 -0800
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On Mon, 11 Jan 2010 15:39:32 -0500, David Jordan wrote:

>I have attached a link to the Ford Mobile Radio Installation Guidelines:
>http://www.fordemc.com/docs/download/Mobile_Radio_Guide.pdf that should help
>you with your mobile installation and ignition noise reduction. The RFI
>Suppression Beads may help with your ignition noise. Often it is the fuel
>injectors that cause the ticking interference and beads have helped in some
>cases. Also, the coil or spark unit maybe treated with beads. Each case is
>different, so you will need to do some experimenting on mobile noise
>suppression. Bonding the engine and the hood to the frame with tinned copper
>braids may also help.

This is pretty good advice, especially the recommendation for bonding between 
pieces of the body that appear to be connected but often are not. Hood hinges 
are a point where bonding is needed because the hinges have little or no 
electrical conductivity! Bonding the hood to the body would thus improve the 
shielding provided by the hood (although the long slots along the side of the 
hood contribute a large break in the shielding, which lets out a lot of RF. 

Note that the Ford piece is generic and more than ten years old. While the 
physics of radio doesn't change, a LOT more electronic systems are built into 
cars today than in 1998. That means more trash and more susceptibility. 

FWIW -- one of my good friends in the broadcast engineering world is Warren 
Schulz, chief engineer at WLS (50kW on 890). At about the time Ford's RFI 
document was written, Warren was telling me that the noise in Ford vehicles 
was so bad that the radios in Ford vehicles couldn't hear his non-directional 
50kW clear channel station ten miles away. 


Jim Brown K9YC 

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