Mobile Antenna Installations - Yaesu FT-847 Operating Manual

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 antennas' support structure(s) adequately,
so as to dissipate energy absorbed during a lightning
strike. Install appropriate lightning arrestors in the
antenna coaxial cables (and rotator cables, if rotary
antennas are used).
In the event of an approaching electrical storm, dis-
connect all antenna lead-in, rotator cables, and power
cables completely from your station if the storm is
not immediately in your area. Do not allow discon-
nected cables to touch the case of your FT-847 trans-
ceiver or accessories, as lightning can easily jump from
the cable to the circuitry of your transceiver via the
case, causing irreparable damage. If a lightning 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 struc-
ture 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 radiating 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 volt-
ages outward from the center of the antenna in the
event of a direct lightning strike.
FT-847 O
PERATING
A C
NTENNA
Photo
Horizontal Loop
for SSB/CW Operation
M
ANUAL
ONSIDERATIONS

Mobile Antenna Installations

Mobile antennas for the HF bands, with the possible
exception 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. Addi-
tional system bandwidth may be realized using the
Yaesu FC-20 Automatic Antenna Tuner, which will
present a 50 impedance to your transceiver on the
1.8 ~ 50 MHz bands so long as the SWR on the co-
axial line connected to the FC-20 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 antenna
matching to 50 be performed at the antenna
feedpoint.
Yaesu's Active-Tuned Antenna System
(ATAS-100) is a unique HF/VHF/UHF mo-
bile antenna system, which provides auto-
matic tuning when used with the FT-847. See
page 62 for full details on the ATAS-100.
For VHF/UHF weak-signal (CW/SSB) op-
eration, remember that the antenna polariza-
tion standard for these modes is horizontal,
not vertical, so you must use a loop or other-
wise horizontally-polarized antenna so as to
avoid cross-polarization loss of signal
strength (which can be 20 dB or more!). On
HF, signals propagated via the ionosphere
develop mixed polarizations, so antenna se-
lection may be made strictly on mechanical
considerations; vertical antennas are almost
always utilized on HF for this reason.
Installation
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