Bedienungsanleitung Yaesu FT-897 (Seite 9 von 72) (Englisch)

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Page 7FT-897 OPERATING MANUAL

INSTALLATION

GROUNDING

The provision of an effective ground system is important in

any successful communications station. A good ground sys-

tem can contribute to station efficiency in a number of ways:

❒

It can minimize the possibility of electrical shock to the

operator.

❒

It can minimize RF currents flowing on the shield of the

coaxial cable and the chassis of the transceiver which

may cause interference to nearby home entertainment

devices or laboratory test equipment.

❒

It can minimize the possibility of erratic transceiver op-

eration caused by RF feedback or improper current flow

through logic devices.

An effective earth ground system may take several forms;

for a more complete discussion, see an appropriate RF engi-

neering text. The information presented below is intended

only as a guideline.

Inspect the ground system – inside the station as well as

outside – on a regular basis so as to ensure maximum per-

formance and safety.

Mobile Station Grounding

Although satisfactory grounding in most installations will

be achieved via the DC cable’s negative lead and the an-

tenna system’s coaxial cable shield, it is often recommended

that you provide a direct ground connection to the vehicle

chassis at the mounting location of the transceiver (installa-

tion using the optional MMB-80 Mounting Bracket will ac-

complish this, if the MMB-80 itself is mounted to the

vehicle’s chassis). Due to unexpected resonance which may

naturally occur in any location, improper communication

system performance may result from insufficient ground-

ing. These symptoms may include:

❒

RF feedback (resulting in distortion on your transmitted

signal);

❒

Unintended frequency change;

❒

Blinking or blanking of the frequency display;

❒

Noise pickup; and/or

❒

ons may occur in any communica-

tions installation. The FT-897 includes extensive filtering

designed to minimize the chance of such problems; how-

ever, random currents set up by insufficient RF grounding

can nullify such filtering. Bonding the rear panel Ground

lug of the FT-897 transceiver to the vehicle or vessel’s

ground system should clear up any such difficulties.

Vertex Standard does not recommend the use of “on glass”

mobile antennas unless the shield of the coaxial cable is se-

curely grounded near the feedpoint of the antenna. Such

antennas frequently are responsible for the ground-related

difficulties described above.

Base Station Earth Grounding

Typically, the ground connection consists of one or more

copper-clad steel rods, driven into the ground. If multiple

ground rods are used, they should be configured in a “V”

configuration, and bonded together at the apex of the “V”

which is nearest the station location. Use a heavy, braided

cable (such as the discarded shield from type RG-213 co-

axial cable) and strong cable clamps to secure the braided

cables to the ground rods. Be sure to weatherproof the con-

nections to ensure many years of reliable service. Use the

same type of heavy, braided cable for the connections to the

station ground bus (described below).

Do not use gas line pipes in an attempt to provide a ground

connection! To do so creates a serious risk of explosion!!

Inside the station, a common ground bus consisting of a cop-

per pipe of at least 25 mm (1”) diameter should be used. An

alternative station ground bus may consist of a wide copper

plate (single-sided circuit board material is ideal) secured

to the bottom of the operating desk. Grounding connections

from individual devices such as transceivers, power sup-

plies, and data communications devices should be made di-

rectly to the ground bus using a heavy, braided cable.

Do not make ground connections from one electrical device

to another, and thence to the ground bus. This so-called

“Daisy Chain” grounding technique may nullify any attempt

at effective radio frequency grounding. See the drawings

below for examples of proper and improper ground connec-

tions. If your coaxial cable does not connect directly to the

station ground bus, you may connect a ground cable to the

Ground lug on the FT-897 rear panel.

Proper Ground Connection

Linear

Am plifier

Pow er

Supp ly

Transceiver

Improper Ground Connection

Transceiver Linear

Am plifier

Pow er

Supply

"Daisy Chain"

GND Terminal

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