Bedienungsanleitung Yaesu FT-897 (Seite 10 von 72) (Englisch)

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Page 8 FT-897 OPERATING MANUAL

ANTENNA CONSIDERATIONS

The antenna systems connected to your FT-897 transceiver

are, of course, critically important in ensuring successful

communications. The FT-897 is designed for use with any

antenna system providing a 50 Ω resistive impedance at the

desired operating frequency. While minor excursions from

the 50 Ω specification are of no consequence, the power

amplifier’s protection circuitry will begin to reduce the power

output of there is more than a 50% divergence from the speci-

fied impedance (less than 33 Ω or greater than 75 Ω, corre-

sponding to a Standing Wave Ratio (SWR) of 1.5:1).

Two antenna jacks are provided on the rear panel of the FT-

897. The “HF/50 MHz ANT” jack is used for HF and 50

MHz, while the “144/430 MHz ANT” jack is used for 144

MHz and 430 MHz.

Guidelines for successful base and mobile station installa-

tions are shown below.

Mobile Antenna Installations

Mobile antennas for the HF bands, with the possible excep-

tion of those designed for 28 MHz, display very high “Q”

due to the fact that they must be physically shortened, then

resonated using a loading coil. Additional system bandwidth

may be realized using the Yaesu FC-30 Automatic Antenna

Tuner, which will present a 50 Ω impedance to your trans-

ceiver on the 1.8 ~ 50 MHz bands so long as the SWR on

the coaxial line connected to the FC-30 is below 3:1.

On the VHF and UHF bands, coaxial line losses increase so

rapidly in the presence of SWR that we recommend that all

impedance matching to 50 Ω be performed at the antenna

feedpoint.

Yaesu’s Active-Tuned Antenna System (ATAS-100/-120)

is a unique HF/VHF/UHF mobile antenna system, which

provides automatic tuning when used with the FT-897. See

page 39 for full details on the ATAS-100/-120.

For VHF/UHF weak-signal (CW/SSB) operation, remem-

ber that the antenna polarization standard for these modes is

horizontal, not vertical, so you must use a loop or otherwise

horizontally-polarized antenna so as to avoid cross-polar-

ization loss of signal strength (which can be 20 dB or more!).

On HF, signals propagated via the ionosphere develop mixed

polarizations, so antenna selection may be made strictly on

mechanical considerations; vertical antennas are almost al-

ways utilized on HF for this reason.

Base Station Antenna Installations

When installing a “balanced” antenna such as a Yagi or di-

pole, remember that the FT-897 is designed for use with an

(unbalanced) coaxial feedline. Always use a balun or other

balancing device so as to ensure proper antenna system per-

formance.

Use high-quality 50 Ω coaxial cable for the lead-in to your

FT-897 transceiver. All efforts at providing an efficient an-

tenna system will be wasted if poor quality, lossy coaxial

cable is used. Losses in coaxial lines increase as the fre-

quency increases, so a coaxial line with 0.5 dB of loss at 7

MHz may have 6 dB of loss at 432 MHz (thereby consum-

ing 75% of your transceiver’s power output!). As a general

rule, smaller-diameter coaxial cables tend to have higher

losses than larger-diameter cables, although the precise dif-

ferences depend on the cable construction, materials, and

the quality of the connectors used with the cable. See the

cable manufacturers’ specifications for details.

For reference, the chart below shows approximate loss fig-

ures for typically- available coaxial cables frequently used

in HF installations.

Loss in dB per 30 m (100 feet)

for Selected 50-ohm Coaxial Cables

Loss

Cable Type 1.8 MHz 28 MHz 432 MHz

RG-58A 0.55 2.60 >10

RG-58 Form 0.54 2.00 8.0

RG-8X 0.39 1.85 7.0

RG-8A, RG-213 0.27 1.25 5.9

RG-8 Form 0.22 0.88 3.7

Belden 9913 0.18 0.69 2.9

7/8” “Hardline” <0.1 0.25 1.3

Loss figures are approximate; consult cable manufacturer’s

catalogs for complete specifications.

Always locate antennas such that they can never come in

contact with outdoor power lines in the event of a catastrophic

support or power-pole structural failure. Ground your an-

tennas’ support structure(s) adequately, so as to dissipate

energy absorbed during a lightning strike. Install appropri-

ate lightning arrestors in the antenna coaxial cables (and

rotator cables, if rotary antennas are used).

In the event of an approaching electrical storm, disconnect

all antenna lead-in, rotator cables, and power cables com-

pletely from your station if the storm is not immediately

in your area. Do not allow disconnected cables to touch the

case of your FT-897 transceiver or accessories, as lightning

can easily jump from the cable to the circuitry of your trans-

ceiver via the case, causing irreparable damage. If a light-

ning storm is in progress in your immediate area, do not

attempt to disconnect the cables, as you could be killed in-

stantly if lightning should strike your antenna structure or a

nearby power line.

If a vertical antenna is utilized, be certain that humans and/

or pets and farm animals are kept away both from the radiat-

ing element (to prevent electrical shock and RF exposure

danger) and the ground system (in the event of an electrical

storm). The buried radials of a ground-mounted vertical

antenna can carry lethal voltages outward from the center of

the antenna in the event of a direct lightning strike.

INSTALLATION

Yaesu FT-897 Seite 10

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