Practical_Antenna_Handbook_0071639586

C h a p t e r 3 0 : G r o u n d i n g f o r S a f e t y a n d P e r f o r m a n c e 687
Figure 30.2 Single-Âpoint ground (SPG) system brings grounds for all utilities, antenna feedlines, and control
lines together at a common entry point for the entire building.
surge voltages on two different cables or within two different systems. As one specific
example, the author lost a fax machine, a cordless telephone base station, and a number
of PCs—each with an internal fax modem card connected to the telephone line—during
thunderstorms on two separate occasions back when his telephone line and ac mains
entered—and were grounded—at opposite ends of his home. The author’s transceivers,
with no connection to the telephone system but with their inputs connected to coaxial
cables in the SPG enclosure, sustained no damage during those same storms.
All radio transmission lines, all rotator control cables, all remote switch control lines
must go through the SPG. At the very least, the GND lead for a set of control wires
should be grounded at the SPG. The same is true for the shield braid of each coaxial
cable entering or exiting the building. Open-Âwire transmission lines should, at a minimum,
have spark gaps from both sides of the line to the SPG ground and ideally would
have remotely operated contactors that short out both sides of the transmission line to
SPG ground when that line is not in use.
“Hot” leads—the center conductor of coaxial cable, the control lines to remote antenna
selectors, rotators, etc.—can be handled either of two ways:
• Use the normally closed contact of relays or contactors to directly ground them
all when they’re not in use.
• Route each and every hot lead through a lightning protection device.