Yaesu FT-7800R, Руководство по эксплуатации

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6 FT-7800R O
PERATING
M
ANUAL
A
NTENNA
C
ONSIDERATIONS
The FT-7800R 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 50 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).
Note that this transceiver is designed with wide frequency coverage in the VHF/UHF spec-
trum. For general listening, you may wish to have a broadband antenna such as a discone
available, as a directional antenna such as a Yagi will have degraded performance outside
the Amateur band for which it is designed.
Excellent reference texts and computer software are available for the design and optimiza-
tion of VHF and UHF 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-7800R
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 under 1 dB of loss at 144 MHz may have a loss of 3 dB or more at 446
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).
I
NSTALLATION