[RFI] Radio "Grounding"

Jim Brown jim at audiosystemsgroup.com
Thu Aug 9 17:45:53 EDT 2007

On Thu, 9 Aug 2007 14:08:56 -0700 (PDT), Michael Germino wrote:

>I would work on the Radio ground last. 

The "need" for grounding a radio is another one of those widely 
repeated myths.  

We DO want a good bond of the shield of coax to the body AT THE 
ANTENNA, we DO want the DC power pair (preferably TWISTED) to go 
straight from the radio to the battery terminals, and we DO want 
the  body of the vehicle to be bonded together very well and at as 
many points as possible. 

But there is NO good reason to bond a radio chassis to the chassis 
of a vehicle. In fact, doing so is more likely to increase noise 
and RFI rather than reduce it. Why? Because the parallel path for 
return current (the body is one path, the direct connection to the 
battery is the other) increases the loop area! 

In a ham shack, bonding all the gear together by a low impedance 
path has one major benefit -- it reduces the AUDIO FREQUENCY 
voltage between them, which reduces current on audio cable 
shields, which in turn reduces AUDIO noise IR drop on those 
unbalanced connections. In other words, it reduces power-related 
hum and buzz when you have that gear plugged into different AC 
outputs and try to feed audio from one box to another. You can 
also reduce that noise voltage by plugging all the gear into the 
same power system outlet box. 


Jim Brown K9YC

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