Antenna Tuner Operation - Icom IC-756PROIII Instruction Manual

10

ANTENNA TUNER OPERATION

■ Antenna tuner operation
The internal automatic antenna tuner matches the
transceiver to the connected antenna automatically.
Once the tuner matches an antenna, the variable ca-
pacitor angles are memorized as a preset point for
each frequency range (100 kHz steps). Therefore,
when you change the frequency range, the variable
capacitors are automatically preset to the memorized
point.
TUNER OPERATION
➥ Push the [TUNER] switch to turn the internal an-
tenna tuner ON. The antenna is tuned automati-
cally when the antenna SWR is higher than 1.5:1.
• When the tuner is ON, the [TUNER] switch lights.
MANUAL TUNING
During SSB operation at low voice levels, the internal
tuner may not be tuned correctly. In such cases, man-
ual tuning is helpful.
➥ Push [TUNER] for 1 sec., to start manual tuning.
• A side tone is emitted and [TUNER] blinks while tuning.
• If the tuner cannot reduce the SWR to less than 1.5:1
after 20 sec. of tuning, the [TUNER] switch indicator
goes out.
AUTOMATIC TUNER START (HF bands only)
If you want to deactivate the tuner under conditions
of VSWR 1.5:1 or less, use the auto tuner start func-
tion and turn the tuner OFF. This function activates
the tuner automatically when the SWR exceeds 1.5:1.
This function is turned ON in set mode. (p. 101).
NOTES:
• If the tuner cannot tune the antenna
Check the following and try again:
• the [ANT] connector selection.
• the antenna connection and feedline.
• the unaltered antenna SWR. (Less than 3:1 for HF bands;
Less than 2.5:1 for 50 MHz band)
• the transmit power. (8 W for HF bands; 15 W for 50 MHz
band)
• the power source voltage/capacity.
If the tuner cannot reduce the SWR to less than 1.5:1
after checking the above, perform the following:
• repeat manual tuning several times.
• tune with a 50 Ω dummy load and re-tune the antenna.
• turn power OFF and ON.
• adjust the antenna cable length.
(This is effective for higher frequencies in some cases.)
89
CAUTION:
NEVER transmit with the tuner ON
when no antenna is connected. This will damage
the transceiver. Be careful of the antenna selection.
[TUNER]
Push [TUNER] for 1 sec.
PTT TUNER START
The tuner is always tuned when the PTT is pushed
after the frequency is changed (more than 1% from
last-tuned frequency). This function removes the
"push and hold [TUNER]" operation and activates for
the first transmission on a new frequency.
This function is turned ON in set mode. (p. 101).
• Tuning a narrow bandwidth antenna
Some antennas, especially for low bands, have a nar-
row bandwidth. These antennas may not be tuned at
the edge of their bandwidth, therefore, tune such an
antenna as follows:
Suppose you have an antenna which has an SWR of
1.5:1 at 3.55 MHz and an SWR of 3:1 at 3.8 MHz.
q Push [TUNER] to turn the antenna tuner ON.
w Select CW mode.
e Turn OFF the break-in function. (pgs. 4, 66)
r Push [TRANSMIT] to set to the transmit condition.
t Set 3.55 MHz and key down.
y Set 3.80 MHz and key down.
u Push [TRANSMIT] to return to the receive condition.