FCC ID: K66FT-857
Operating Manual
Vertex Standard Co., Ltd.
8
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-857. See page 39 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.
Base Station Antenna Installations
When installing a “balanced” antenna such as a Yagi or dipole, remember that the FT-857 is designed for use with an
(unbalanced) coaxial feedline. Always use a balun or other balancing device so as to ensure proper antenna system
performance.
Use high-quality 50
Ω
coaxial cable for the lead-in to your FT-857 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 a coaxial line with 0.5 dB of loss at 7 MHz may have 6 dB of loss at 432 MHz (thereby
consuming 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 differences 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 figures 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
2.6
>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.
