[RFI] Radio "Grounding"
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
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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