On Sun,9/27/2015 2:32 PM, Bob McGraw - K4TAX wrote:
I agree with Fred in that there is no one system or method that "fits
all". In general I view station grounding approaches as 4 different
systems, all which should be implemented.
(a) All driven grounds must be bonded to each other an to the AC
Mains ground and this should occur outside of the structure or house.
I find no exception to this practice unless a tower is 200 ft or more
from the structure at which point a ground system should be located at
the base of the tower.
(b) Third pin green wire or safety ground for equipment must always
be in place and not "cheated" with an adapter.
(c) All lightning protection should occur before any feed line or
rotor control enters the building. Its ground attachment should be
part of the driven ground and bonding system. Towers should have a
ground from top to bottom and not relay solely on the structure
alone. Don't forget to bond the rotating mast out the top of the
tower to the tower itself.
Yes, and to clarify, ALL of those grounded points MUST be bonded together.
(d) Certain type of antennas do require a specific ground system
which I refer as RF Ground. A few driven ground rods do not make a
RF Ground. Those being, but not solely inclusive, verticals,
slopers, end fed Zepps, long wires and such as examples.
Another clarification. What you're calling a ground system for an
antenna is NOT a ground system at all. Rather, a radial system functions
two ways -- it acts as a low loss return for antenna current and and as
a return for the fields produced by the antenna. In other words, a
radial field SHIELDS the antenna and its fields from lossy earth so that
power is not wasted in the soil under the antenna. In the absence of a
radial system, we often use a COUNTERPOISE -- a wire connected to the
return side of the coax (or the antenna tuner) to act as the return for
current. The primary difference is that the counterpoise is simply
another radiating part of the antenna, but it does not provide the
shielding function.
Yes, broadcast radial systems are usually buried, but the skin depth of
soil usually extends FAR below the topsoil on the AM broadcast band and
on 160M, so the radial system is still providing the low loss return and
shield. Another benefit of radial systems is that they provide
capacitive coupling to a wide area around an antenna, which improves the
path to ground for lightning.
73, Jim K9YC
73, Jim K9YC
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