On 3/21/2014 1:34 AM, Jim Brown wrote:
All of the replies I've seen here are obsessing on the wrong topic. By
all means DO take care to avoid oxidation and dissimilar metals
problems. But that ground bar, whatever it is, is NOT an important
element of what you're doing, which is primarily LIGHTNING
SUPPRESSION, but also minimizing hum, buzz, and RFI.
What matters is that EVERY CHASSIS in your shack be bonded together by
short fat copper, and that combination of chassis bonded to everything
in your house by short fat copper. That includes antenna entry, every
ground rod, the power system ground, the telco ground, the CATV
ground, the satellite ground, structrural steel ground (if any), and,
if your tower is close to the house, the tower ground.
You are also forgetting that bonding between equipment should also be
short, fat copper. When you run wires from each piece of gear to a bar
at the back of he desk, that usually makes the connection more than
twice as long. That means double the resistance and double the
inductance. NOT a good thing.
I was taught to use as short as possible ground from each piece of
equipment to a common point, equidistant from each piece of equipment.
The idea is not to prevent the equipment from rising above ground, but
rather, rising to the same potential at the same time.
Regardless of the ground system, induced voltages may differ from one
end of the house to the other by thousands of volts. The more rapid the
riser time (Dv/Dt) the greater the voltage difference. The goal is to
get all equipment at any one location at the same voltage at the same time.
Ideally we'd have a Single Point Ground (SPG) for every building, but
that's rarely possible. Given the telephone and internet lines may
connect to all the electronic equipment (or most of it) we may have 3 or
4 sources in a piece of equipment, such as ham station, TV, and
computers. They may all be grounded, but unless it's a common point
that is equidistant from each piece of equipment the odds are there will
be substantial voltage between services.
However, when it come to all the other equipment in the house, TV,
Stereo, telephone, Internet, network, Hot water heater and in-sundry
other things, it is downright impossible.
Power, telephone, and internet come in on one side, while Antennas,
control cables, and network enter/leave on the opposite side. TV is on a
side by itself. The grounds are tied together, but distance make the
voltage difference via Dv/Dt to be substantial. That TV has Antennas at
opposit ends of the house with 2 at 95 feet, telephone line, internet,
cable, and electrical service.
73
Roger (K8RI)
The BEST bonding method in the shack is short, fat copper from chassis
to chassis of every piece of gear in the shack, then a bond from one
of those chassis (preferably the rig) to those other grounds in your
home. Chassis to chassis bonding minimizes hum, buzz, and RFI. Bonding
all the grounds together and to earth provides lightning safety.
73, Jim K9YC
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