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Re: [RFI] Mobile amps and vehicle issues

To: "RFI List" <rfi@contesting.com>
Subject: Re: [RFI] Mobile amps and vehicle issues
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Thu, 12 Jan 2006 13:08:14 -0600
List-post: <mailto:rfi@contesting.com>
On Thu, 12 Jan 2006 10:25:41 -0800 (PST), Michael Germino wrote:

>So that everyone is not scared away from HF mobile with the newer
>vehicles, I would like to say that I have three GMC gas engine 
>pickups in the last 16 years and they all have been very quiet.

Yes. My Volvo S80 received NO RFI from my 100w HF rigs, and was 
moderately quiet with NO filtering at all by me. If I hadn't given 
it to my XYL's daughter, I would have dug in and cleaned some of 
the receive noise out. 

>  Only problem I have had was years ago running CW with an amp 
changed the speed on  the cruise control.
>  1. Route cables and coax away from EVERYTHING.
>  2. Proper antenna location and GROUNDING of the antenna.
>  3. Use Ferrite beads on the cables and coax.
>  4.  Ground your equipment properly.
>  For my situations these are my order of importance.  (Just as 
an experiment, I have disconnected the radio equipment ground and 
didn't notice any difference with 100 Watts HF)

IMO, "grounding" a radio transmitter or receiver to the body of a 
vehicle makes NO contribution to noise, RFI, or the lack of it, 
except to the extent that the coax may not be properly decoupled 
from the antenna. What DOES contribute are your items #1, #2, and 
#3 above. Indeed, it is the bonding of the antenna that makes the 

To your list I would add RF filtering/choking/bypassing of 
sensitive and noisy wiring on the vehicle. And because I believe 
strongly in not messing with a system any more than necessary, my 
filtering/bypassing/choking is generally limited to suitable 
ferrite parts as noted. Indeed, because the body carries RF 
antenna current, bypassing to the body can easily cause as many 
problems as it cures. 

Jim Brown K9YC

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