> While the chassis serves as an acceptable return for DC current, using
> it in this manner is a recipe for AC problems, like alternator whine
> and RFI.
In addition, it's a recipe for ignition noise and corona noises since
using the chassis of the vehicle as a DC return makes every noise
source in the vehicle (plus antenna return currents) "common" to the
transceiver power supply. Consider the impedance between the
transceiver's chassis connection and the negative terminal of the
battery to be equivalent to the modulation choke in an old AM
transmitter ... every noise and all of the antenna "return" current
modulates the DC reference (DC return) of the transceiver!
Proper installation of communications equipment calls for separately
fused power connections directly to both terminals of the battery
and a substantial common mode choke in the antenna feedline at the
feedpoint of the antenna.
73,
... Joe, W4TV
On 4/2/2011 1:45 PM, Jim Brown wrote:
> On 4/2/2011 3:40 AM, James Maynard wrote:
>> In fact, boats are quite different from cars. In cars, it is common to
>> use the chassis as a common ground return. In boats, this is forbidden.
>
> While the chassis serves as an acceptable return for DC current, using
> it in this manner is a recipe for AC problems, like alternator while and
> RFI. Ham gear should ALWAYS be powered by paired conductors running
> directly from the power source, preferably a twisted pair.
>
> 73, Jim Brown K9YC
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