D Optional External Tuner Operation; D Optional; Automatic Antenna Tuner; Operation - Icom IC-703 Instruction Manual

9
ANTENNA TUNER OPERATION

D Optional external tuner operation

The IC-703 automatically detects and selects an optional
external tuner (AT-180/AH-4) when connected. In this
case, the internal tuner switches to the through function.
NOTE: When the connected power supply voltage
is lower than 11.0 V, the transceiver automatically
switches to the battery operating mode (power sav-
ing mode). In this case, the transceiver can not drive
an external antenna tuner.
D Optional AT-180
The AT-180 automatic antenna tuner matches the IC-
703 to the connected antenna automatically. Once the
tuner matches an antenna, the variable capacitor an-
gles are memorized as a preset point for each fre-
quency range (100 kHz steps). Therefore, when you
change the frequency range, the variable capacitors
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.
• The AT-180 can match both HF and 50 MHz bands.
However, operation is different for the HF and 50
MHz bands.
TUNER OPERATION
• For the HF band:
Push [TUNER] to turn the tuner ON. The antenna is
tuned automatically during transmission when the an-
tenna SWR is higher than 1.5:1.
• When the tuner is OFF, the [TUNER] light goes out.
TUNER
[TUNER]
• For the 50 MHz band:
Push [TUNER] for 1 sec. to tune the antenna. If the
[TUNER] light flashes slowly while transmitting, push
and hold [TUNER] for 1 sec. again to re-tune the an-
tenna.
TUNER
[TUNER]
65

AUTOMATIC ANTENNA TUNER

Lights to indicate AT-180
is turned ON.
Flashes to indicate
re-tuning is necessary.
NOTE: When connecting the optional antenna tuner
AT-180, the IC-703's output power must be set max-
imum (10 W) both in quick set mode and initial set
mode. Otherwise, the AT-180 may not be tuned cor-
rectly.
(AT-180's minimum operating input power is 8 W.)

operation

MANUAL TUNING
During SSB operation on HF bands at low voice lev-
els, the AT-180 may not be tuned correctly. In such
cases, manual tuning is helpful.
Push [TUNER] for 1 sec. to start manual tuning.
• CW mode is selected, a side tone is emitted, and the
[TUNER] light flashes; then, the previous mode is selected.
[TUNER]
Push and hold for 1 sec. to start manual tuning.
If the tuner cannot reduce the SWR to less than 1.5:1
after 20 sec. of tuning, the [TUNER] light goes out. In
this case, check the following:
• the antenna connection and feedline
• the antenna SWR (p. 55; meter function)
Through inhibit (HF bands only)
The AT-180 has a through inhibit condition. When se-
lecting this condition, the tuner can be used at poor
SWR's. In this case, automatic tuning in the HF bands
activates only when exceeding SWR 3:1. Therefore,
manual tuning is necessary each time you change the
frequency. Although termed "through inhibit," the tuner
will be "through" if the SWR is higher than 3:1 after
tuning.
CONVENIENT
• Tuner sensitive condition (HF bands only)
If you require critical tuning at any time during trans-
mission, select the tuner sensitive condition. See
p. 81 for selection.
• Automatic tuner start (HF bands only)
If you want to turn OFF the tuner under conditions of
VSWR 1.5:1 or less, use "automatic tuner on" and
turn the tuner OFF. See p. 81 for turning the function
ON and OFF.