[RFI] Radio "Grounding"

kd4e doc at kd4e.com
Thu Aug 9 17:54:44 EDT 2007

 > Tom Rauch wrote:
>> Would a 95%+ shielded DC cable, grounded at both ends, be the
>> effective equivalent?

I should have typed "shield grounded at one end".

> Why would you want to do that and what would you gain?
> Isn't the radio dc input properly bypassed?
> ... snip ...
> Most accessories outside of the engine compartment ties to the chassis 
> and return through the small ground lead to the chassis. This means fuel 
> pumps, lights, horns, wipers, seat motors, window heating tapes, the 
> stereo, wiper motor, heater motor, and many other things return through 
> that chassis lead to the battery.
> When you connect the radio negative to the battery  negative post you 
> now have a second path for all those accessories to return through the 
> radio to the battery. This path is either through a cabinet ground on 
> the radio, through the antenna lead, through an accessory jack like an 
> external speaker, or even a key jack.
> ... snip ...
> A far better approach is to bond the radio negative lead to the vehicle 
> chassis. The best place is generally near the battery to chassis ground, 
> or on a primary piece of sheetmetal that is part of the main structure 
> of the vehicle. This keeps the radio negative power lead at the SAME 
> ground potential as the antenna or any accessories (like a speaker) that 
> you might plug into the radio. In this case there is no ground loop 
> through the radio.
> ... snip ...

Too much plastic and too broad an input in a FT-857D (not to mention
the vulnerabilities of the boatanchor AM rig I am considering running
in the van on occasion ... just for fun!

Both are likely to be very friendly to vehicle computer and other
wonderful modern electronic noise sources.

Presuming that I connect the negative as you have described I would
anticipate the role of the shield on the DC cable as a way to avoid
radiated noise getting into the DC line on the way to the rig.


Thanks! & 73, doc, KD4E
Personal: http://bibleseven.com/kd4e.html

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