Transmitting; Automatic Antenna Matching - Yaesu FT-920 Operating Manual

Transmitting

Now that you are familiar with receiver operation, we
shall explore the FT-920's capabilities in the transmit
mode.
Important Note!
Whenever you transmit, be certain to have a
suitable antenna or 50
nected to the antenna jack in use. Although
the FT-920's final amplifier protection circuitry
will drastically reduce power if no load is
present, there still is a slight chance of dam-
age to your equipment in the unlikely event of
a catastrophic protection-circuitry failure.
The transmitter can be activated within an amateur
bands. When tuned to any other frequency, the trans-
mitter will be disabled. You, as the station control
operator, are responsible to restrict your transmis-
sions to those frequencies on which you are autho-
rized to operate.
Attempting to transmit outside of an amateur band
segment will cause the "E
RROR
to appear on the display.
Whenever the transmitter is activated, the FT-920's
built-in directional coupler detects any reflected power
which appears at the final amplifier's output port (due
to antenna system impedance mismatch), and dis-
ables the transmitter if too much reflected power is
found (in which case the [H
illuminated). You should cease transmission imme-
diately, and determine the cause of the antenna sys-
tem fault.
The upper limit of the transmitter's power output
can be set via Menu Items U-49 (for Antenna A)
and U-50 (for Antenna B) separately for each an-
tenna port. See page 79 for details.
FT-920 Operating Manual
dummy load con-
" diagnostic message
SWR] icon will become
I

Automatic Antenna Matching

The built-in automatic antenna tuner unit is capable
of matching antenna systems presenting impedances
within the range 16.5~150 , which corresponds to a
maximum SWR or approximately 3:1. If the
antenna(s) you re using exceed this SWR as config-
ured, you must make adjustments (electrical and/or
mechanical) so as to present an impedance closer
to 50 to the FT-920's A
NTENNA
that the net SWR as detected by the FT-920 may be
different than the SWR at the antenna feedpoint,
depending on the degree of impedance transforma-
tion which may occur in your feedline (if the feedpoint
impedance is not very close to the coaxial cable's 50
impedance).
Note that the FT-920's automatic antenna tuner is
not designed to cope with the wide variations in im-
pedance presented by a random-length long wire
antenna, unless you take specific steps to match the
impedance at all frequencies of interest.
To use the FT-920's automatic antenna tuner:
Turn the RF P control fully clockwise (the
WR
transceiver will automatically reduce its power
to a maximum of 50 Watts during antenna tun-
ing).
Check to be certain that the frequency is clear
before initiating antenna tuning.
Press and hold in the T
ond to activate the tuner. The RX T
indicator will appear on the display.
A carrier will now be transmitted by the FT-
920. The automatic antenna tuner will now
adjust itself so as to present a low SWR to the
final amplifier stage. The "W
appear on the display during tuning.
When tuning is completed, the "W
tor will disappear, and the FT-920 will revert to
the receive mode. At this point, if the tuner
achieved an SWR of less than 1.5:1, the tuner
settings will be stored by the tuner's memory
system; these settings will be used the next
time operation takes place on this frequency.
If the tuner was not able to achieve an SWR of
1.5:1 or lower (typically only when the "Tuner-
Off" SWR is above 3:1), the tuner's memory
system will ignore these settings, and the tun-
ing procedure should be repeated the next time
jack(s). Remember
switch for ½ sec-
UNER
TX
UNER
" indicator will
AIT
" indica-
AIT
47