INSTALLATION
ANTENNA CON SID ERA TIO NS
The FC-757AT and FAS- l -4R Remote Antenna
Selector are designed for unbalanced RF feedlines.
For antennas that require balanced feed, or for
connecting balanced feedlines to this equipment,
balun transformers are recommended. Such baluns
should be designed to provide the nearest possible
match to 50 ohms at the unbalanced side, and then
50-ohm coax should be used to make connections
to the equipment. In such cases, where a portion
of the feedline is open-wire type, the length of
coax used should be as short as possible in relation
to the open-wire portion, to minimize feedline loss
in high SWR conditions.
While the range of SWRs that the FC-7 5 7 AT is
able to match is quite wide, antenna systems that
are very far from resonance at the operating
frequency may present too high an SWR to permit
proper matching with the Tuner. In such cases it is
best to retune the antenna itself, or use it only on
the bands where it matches easily, installing
another antenna for the desired band. If the Tuner
is not able to bring the SWR down below 3: 1,
attempting to transmit will result in an automatic
reduction of power in the transmitter, high power
loss in the coaxial feedline, and unfavorable stress
(high voltage) on the RF components in the Tuner.
Operation under such conditions is not recom
mended.
The F AS-1-4 R is designed to allow remote selec
tion of up to four additional antennas, with only a
single feedline and control cable from the FC-
757 AT to the FAS- l -4R. Once set, the correct
antenna for each band is selected automatically
whenever the operating band is changed in the
Tuner.
ACC-2
INTERCONNECTIONS
Figures 1 through 4 on the following pages
illustrate the interconnections between various
models of HF equipment and the FC-757AT, and
optional F AS- l -4R. When setting up the station,
be sure to install the earth ground connections to
the FC-757AT and Transceiver, as well as the
cables shown.
Figures 1 and 2 illustrate the interconnections with
the FT-757GX and FT-980, respectively. Control
cable C, for connecting the FT-757GX to the
FC-757AT, is supplied with the Tuner. However,
the control cable required for connecting the
FT-980 ACC-1 jack to the FC-757AT (for auto
matic power switching and band selection) is
optional.
Figures 3 and 4 illustrate the interconnections of
the FC-757AT when used with equipment that is
not designed to provide power and automatic
bandswitching signals for the Tuner. In these cases,
supplied DC power cable B is used to connect the
Tuner to a separate source of DC ( 12 to l 5V at
300 mA, or 400 mA with the FAS- l -4R), and
power switching and band selection are controlled
only by the buttons on the front panel of the
FC-757AT. Of course the FT-75 7GX or FT-980
may also be used in this way, without the auto
matic functions.
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