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Yaesu FT-991 Manual

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Page 61
FT-991 OperaTing Manual
The Automatic Antenna Tuner (hereinafter referred to as the “ATU”) built into each
FT-991
is designed to ensure a 50-
Ohm load for the nal amplier stage of the transmitter. We recommend using the ATU whenever operating the
FT-991
.
Advice:
Because the ATU of the
FT-991
is located inside the station, it only adjusts the impedance presented to the trans-
ceiver at the station end of your coaxial cable feedline. It does not “tune” the SWR at the antenna feed point itself.
When designing and building your antenna system, we recommend that every effort be made to ensure a low SWR
at the antenna feed point.
The ATU of the
FT-991
includes 100 memories for tuning data. Eleven of these memories are allocated, one for
each Amateur band, so that each band has at least one setting preset for use on that band. The remaining 89 memo-
ries are reserved for the 89 most-recent tuning points, for quick frequency change without the need to retune the
ATU.
The ATU in the
FT-991
is designed to match impedances within the range of 16.7 Ohms to 150 Ohms, correspond-
ing to an SWR of 3:1 or less on the 160 through 6 meter amateur bands. Accordingly, simple non-resonant whip an-
tennas, along with random-length wires and the “G5RV” antenna (on most bands) may not be within the impedance
matching range of the ATU.
Atu operAtion
usinG the autoMatic antenna tuner
1. Use the Main Tuning Dial knob to set the radio to
the desired operating frequency within the Amateur
band.
2. Press the
TUNE
button momentarily to place the
ATU in the transmit line (no adjustment/tuning will
occur yet). The “
TUNER
” icon will appear in the
display.
quick point:
The momentary press of the
TUNE
button will turn
the tuner on, and the microprocessor will automati-
cally select the tuning point closest to the current
operating frequency.
TUNE Button
3. Press and hold in the
TUNE
button for one second to
begin automatic tuning. The transmitter will be en-
gaged, and the “
TUNER
” icon will blink while tun-
ing is in progress. When the optimum tuning point
has been reached, the radio will return to receive,
and the “
TUNER
” icon will again glow steadily (in-
stead of blinking).
4. To disconnect the ATU from the transmit line, press
the
TUNE
button momentarily. The “
TUNER
”
icon will turn off, conrming that the ATU has been
turned off. In the “Off” mode, the transceiver will be
directly connected to the coaxial cable connected to
your antenna, and will respond to whatever imped-
ance is present at the station end of the coax.
Advice:
The ATU circuit is located between the nal amplier
and the rear-panel antenna jack; reception is not affected
by the ATU.
quick pointS:
As shipped from the factory, only one ATU alignment
point is saved on each Amateur band. This was memo-
rized during the nal alignment and performance veri-
cation stages on the production line.
note:
Please listen to the operating frequency before begin-
ning the tuning process, to be sure you are not interfer-
ing with others who may already be using the frequency.
terMinology:
Antenna Tuner Memories: The ATU microprocessor
makes a note of the selected tuning capacitors and in-
ductors, and stores the data for each 10 kHz window in
which tuning has occurred. This eliminates the need to
re-tune every time you return to a frequency on which
you have already completed the tuning process.
… 63 …


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