On 5/17/2012 1:13 PM, Stuart Rohre wrote:
Jim I respectfully disagree, as I have seen examples of radiating
"ground" wires causing RFI.
Since you didn't quote any part of an email, I have no idea what you're
disagreeing with (or even whether it's me or another Jim that you're
disagreeing with).
That said -- a wire going to ground is no different from any other
wire. If it carries RF current, it will radiate, and it can carry a lot
of RF current if we allow it to become part of a transmitting antenna
system. The most common way that happens is by using a long wire or
vertical antenna and forgetting to provide a counterpoise for antenna
current. When we do that, anything connected to the transmitter chassis
becomes the counterpoise by default.
SO -- if a "ground" conductor is radiating, it's an ANTENNA problem, not
a "grounding" problem. The ground wire(s) MUST be there for reasons of
lightning protection and electrical safety.
Example -- back when I lived in Chicago, my shack was on the second
floor, my antennas were bonded to a station ground, which was bonded to
power, telco, some rods, and a big wrought iron fence that ran around
the front of my lot. My 160M antenna was a vertical random wire formed
by tying both sides of the feedline together and loading it against that
combination of grounds (including the fence). The big #4 copper that
ran from the second floor shack to those grounds and that fence WAS part
of the antenna, even though it was CALLED a "ground" wire, and it
contributed to the total radiation.
Another point. A radiating wire does not CAUSE RFI. Badly designed
equipment causes RFI, either by letting RF into the box, or by emitting
RF trash from the box.
73, Jim Brown K9YC
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