FT-920 Operating Manual
48
you operate on this frequency; this feature pre-
vents you from storing an undesirable setting
(such as that produced when you accidentally
select the wrong antenna on a particular band).
How the Automatic Antenna Tuner Works
When the TUNER switch is pressed and the RX TUNER TX indicator is displayed, the following operations
take place:
A. The tuner’s microprocessor reviews the current the tuning conditions (if any) stored in memory, and
applies the settings for the frequency closest to the current frequency as a starting point for operation.
Note that a change in tuning conditions is produced for every change in operating frequency of ap-
proximately 10 kHz.
B. If transmission occurs (without the operator pressing the TUNER key), the tuner will begin adjustments
if the SWR is found to be 3:1 or greater. Tuner settings will not be recorded in this instance. If, however,
the TUNER key is pushed and held in for ½ second, the tuner settings
will
be stored in the tuner’s
memory system.
C. If tuning is successfully accomplished, and the tuner settings stored into memory, the antenna system
characteristics as seen from the transmitter’s perspective resemble curve (1) in the graph below. If
you QSY to frequency (2) in the chart (where the SWR is above 3:1), the tuner will be automatically
activated when you begin to transmit.
D. The automatic antenna tuner has 100 dedicated tuner memory registers, of which eleven are allocated
(one each) to the amateur bands covered by the FT-920. The other 89 record the most recent tuner
settings, irrespective of the band in use, on a first-in, first-out basis.
E. The automatic antenna tuner is configured at the factory to be engaged both on receive
and
transmit.
It is possible, however, to configure it so that the tuner is only active on transmit. See Menu Item U-48,
described on page 79.
F. The automatic antenna tuner only adjusts the
apparent
SWR as presented to the transceiver. No
adjustments made by the tuner can, of course, affect the SWR present on the coaxial feedline. There-
fore, every effort should be made to minimize SWR so as to ensure efficient power transfer to the
antenna feedpoint (since feedline losses may escalate rapidly as SWR increases).
G. Because the impedance of such antennas varies widely depending on the band in use, please note
that random-length long-wire and center-fed
flat-top antenna systems generally will not be
satisfactorily tuned by the FT-920’s automatic
antenna tuner unless you make design provi-
sions for ensuring that the impedance stays
within the specified range of 16.5 ~ 150 Ω.
Should you wish to take the antenna tuner out
of line, press the TUNER switch momentarily.
The RX TUNER TX indication will disappear from
the display.
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