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Re: [RFI] Auto quieting

To: rfi@contesting.com
Subject: Re: [RFI] Auto quieting
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Mon, 5 Oct 2015 00:19:25 -0700
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On Sat,10/3/2015 6:28 PM, Michael Coslo wrote:
Anyone have any ideas?

From an RFI/EMC point of view, I strongly recommend floating the radio from the vehicle frame, powering it with a twisted pair of big copper straight from the battery to the radio, with the only connection to the chassis being the coax shield at the antenna. Even better, add a high quality RF capacitor between the shield and the chassis. What this does is cause everything above low audio frequencies to return on the return side of the DC pair rather than on the chassis/frame.

In addition, I would also put SERIOUS multi-turn ferrite chokes on that DC cable near the battery, and also on the coax where it feed the antenna.

Fundamental principle -- you want the chassis/frame of the vehicle to be a counterpoise for the antenna, but you don't want it to carry DC or AC current, and you don't want any of the wiring you have added to be a receiving antenna for the RF you are transmitting, nor to radiate the noise on the chassis or other wiring.

73, Jim K9YC

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