Specifications

12 FT-857D Operating Manual
ANTENNA CONSIDERATIONS
The antenna systems connected to your FT-857D transceiver are, of course, critically im-
portant in ensuring successful communications. The FT-857D 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 specified impedance (less than 33 Ω or greater than 75 Ω,
corresponding to a Standing Wave Ratio (SWR) of 1.5:1).
Two antenna jacks are provided on the rear panel of the FT-857D. 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 installations are shown below.
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. Additional system bandwidth may be realized using the
Yaesu FC-30 Automatic Antenna Tuner, which will present a 50 Ω impedance to your
transceiver 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 mo-
bile antenna system, which provides automatic tuning when used with the FT-857D. See
page 68 for full details on the ATAS-100/-120.
For VHF/UHF weak-signal (CW/SSB) operation, remember 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-polarization 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 always utilized on HF for this reason.
In mobile (and portable) installations, when vertical antennas are used, remember that the
grounding of the base area of the antenna is critically important to proper operation. Since
most HF vertical antennas emulate a quarter-wavelength “monopole” antenna, the “miss-
ing half” of the dipole antenna consists of a counterpoise of radial ground system. In a
vehicle, if mounting the antenna to a door or hatch, it is recommended that you bond the
INSTALLATION