Icom IC-756 - Manual (Page 42)

■ 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 ca-
pacitors are automatically preset to the memorized
point. CAUTION: NEVER transmit with the tuner ON
when no antenna is connected. This will damage
the transceiver. Be careful of the antenna selection.
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4
RECEIVE AND TRANSMIT
TUNER OPERATION
Push the [TUNER] switch to turn the internal antenna
tuner ON. The antenna is tuned automatically when
the antenna SWR is higher than 1.5:1.
- When the tuner is ON, the [TUNER] switch lights.
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 function
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. 57).
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. 58).
Push [TUNER].
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 2 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.
Push [TUNER] for 2 sec.
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.)
• 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. (p. 3)
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.