Cooling System Requirements - Harris ZX2500 Technical Manual

Zx series fm

Table of Contents

ZX Series

Lightning and transient energy via the power line or tower connections can impose

serious threats to personnel safety, as well as damage the equipment. For these reasons,

a good protective grounding system to divert these forms of energy to earth ground is

imperative. The energy in a lightning strike has a very fast rise time and can have

frequency components up to the megahertz range. For this reason, it is always preferred

to use straight, direct runs of large, flat conductors so as to minimize inductance and

allow the free passage of transient energy to earth. Note that the small cross-section and

non-direct path to ground of the green/yellow wire of the AC safety ground make it an

unsuitable means for safely diverting the transient energy present during a lightning

strike.

A good grounding system should include substantial grounding at the tower base using

copper ground rods and/or a buried copper ground screen, with copper strap used to

connect the tower base to earth ground. Coaxial cable shield(s) should be electrically

connected to and exit the tower as near to the bottom as practical to minimize the

lightning voltage potential carried by the cable back to the transmitter building.

Ideally, a common grounding plate (bulkhead panel) with a low impedance connection

to building earth ground should be the entry point to the transmitter building for all

signal lines, including AC mains. It should serve as a single-point ground for all

coaxial and mains surge protection devices. Wide copper straps should be used for

making the connection from the common grounding plate to earth ground.

A good ground system should include perimeter grounding of the transmitter building

using copper ground rods and copper strap. There should also be a copper strap running

from tower ground to the building perimeter ground.

A ground system that has been in place for a long period of time can deteriorate and

should be inspected periodically. This is especially true at the point where the ground

strap enters or exits the building. All ground connections should be bolted and brazed

together.

Good grounding and shielding practices will also help keep stray RF current to a

minimum. RF interference usually shows up as intermittent problems with digital/

control circuits, spurious radiated emissions, or audio/video noise if analog signals are

present. Even a small amount of non-shielded wire makes a very efficient antenna for

RF and transient energy. Wire and cable shields should be connected at both ends to the

equipment chassis.

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