Bedienungsanleitung Yaesu FT-2800 (Seite 8 von 60) (Englisch)

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6 FT-2800M OPERATING MANUAL

ANTENNA CONSIDERATION

The FT-2800M is designed for use with antennas presenting an impedance of near 50 Ohms

at all operating frequencies. The antenna (or a 50 Ohm dummy load) should be connected

whenever the transceiver is turned on, to avoid damage that could otherwise result if trans-

mission occurs accidentally without an antenna.

Ensure that your antenna is designed to handle 65 Watts of transmitter power. Some mag-

netic-mount mobile antennas, designed for use with hand-held transceivers, may not be

capable of withstanding this power level. Consult the antenna manufacturer’s specification

sheet for details.

Most all FM work is performed using vertical polarization. When installing a directional

antenna such as a Yagi or Cubical Quad, be certain to orient it so as to produce vertical

polarization, unless you are engaged in a special operating situation where horizontal polar-

ization is used. In the case of a Yagi antenna, orient the elements vertically for vertical

polarization; for a Cubical Quad, the feedpoint should be at the center of one of the vertical

sides of the driven element (or at a side corner, in the case of a diamond-shaped Cubical

Quad).

Excellent reference texts and computer software are available for the design and optimiza-

tion of VHF antennas. Your dealer should be able to assist you with all aspects of your

antenna installation requirements.

Use high-quality 50 Ohm coaxial cable for the lead-in to your FT-2800M transceiver. All

efforts at providing an efficient antenna system will be wasted if poor quality, lossy coaxial

cable is used. Losses in coaxial lines increase as the frequency increases, so an 8-meter-long

(25’ coaxial line with 1/2 dB of loss at 29 MHz may have a loss of 1.8 dB or more at 146

MHz; choose your coaxial cable carefully based on the installation location (mobile vs.

base) and the overall length of the cable required (for very short runs of cable in a mobile

installation, the smaller, more flexible cable types may be acceptable).

For reference, the chart at the right shows ap-

proximate loss figures for typically-available

coaxial cables frequently used in VHF instal-

lations.

In outdoor installations, be certain to weather-

proof all connectors thoroughly, as water en-

tering a coaxial cable will cause losses to es-

calate rapidly, thus diminishing your commu-

nications effectiveness. The use of the shortest

possible length of the highest quality coaxial

cable that fits within your budget will ensure the best performance from your FT-2800M.

INSTALLATION

CABLE TYPE

RG-58A

RG-58 Foam

RG-213

RG-8 Foam

Belden 9913

Times Microwave LMR-400

7/8” “Hardline”

LOSS: 144 MHZ

6.5

4.7

3.0

2.0

1.5

0.7

Loss in dB per 30 m (100 feet) for

Selected 50-Ohm Coaxial Cables

(Assumes 50-ohm Input/Output Terminations)

Loss figures are approximate; consult cable manu-

facturers’ catalogs for complete specifications.

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