Icom IC-720A Instruction Manual page 36

9-3 TRANSMITTER ADJUSTMENT
First, connect an RF wattmeter (impedance of 50 ohms)
to the antenna connector. |
9-3-1 IDLING CURRENT ADJUSTMENT
Place the set in the transmit mode in USB or LSB, 14MHz
band, the RF POWER and the MIC GAIN controls fully
counterclockwise.
(a) Connect a digital voltmeter, in the 10 millivolt range,
across R13 next to the cooling fan. Adjust R12 in the
PA unit to obtain 7 millivolts on the meter. This makes
600mA idling current of the PA transistors.
PA unit
R12
Adjust idling current Connect digital
voltmeter
(b) Connect a digital voltmeter, in the 100 millivolt range,
across R20 in the DRIVER unit. Adjust R13 in the
DRIVER unit to obtain 30 millivolts on the meter.
This makes 100mA idling current of the driver tran-
sistors.
DRIVER unit
R20
Connect digital
voltmeter
R13
Adjust idling
current
9-3-2 ALC (RF POWER) ADJUSTMENT
Place the set in the transmit mode іп RTTY, 14MHz band,
the RF POWER control fully clockwise (just before click
OFF), and S7 on the MIC GAIN board in HI position.
(а) Adjust R9 on the MIC GAIN board for 100 ~ 110 watts
output.
(b) Turn the RF POWER control fully counterclockwise,
and adjust R6 on the MIC GAIN board for 5 ~ 10 watts
output.
-33-
(с) Set the mode to АМ, and turn the КЕ POWER control
fully clockwise and click OFF. Adjust R13 on the MIC
GAIN board for 35 ~ 45 watts output.
(d) Set the band to 28MHz and the mode to RTTY. Ad-
just R11 on the MIC GAIN board for 100 ~ 110 watts
output.
R11
Adjust for 28MHz 100W
R13
Adjust for AM 40W
R9
Adjust for 100W
кб
Adjust Тог 10W
9-3-3 CARRIER SUPPRESSION ADJUSTMENT
Place the set in the transmit mode in USB or LSB, 14MHz
band, the RF POWER and the MIC GAIN controls fully
counterclockwise. Connect an RF voltmeter (set to a high
voltage scale) across Pin 1 of J3 in the DRIVER unit and
ground. With an appropriate meter range to have suitable
deflection for reading, adjust R101 and R106 in the IF unit
for minimum in both USB and LSB modes.
J3, Pin 1 Connect
RF voltmeter
DRIVER unit
АА ty 94 E эшо У
|Е unit
R106 R101
Adjust for carrier null
9-3-4 CARRIER POINT ADJUSTMENT
Place the set in transmit in USB at 14MHz and turn the
RF POWER control fully clockwise and click OFF (COMP
OFF), and the MIC GAIN control in the center (12 o'clock)
position. Connect the AF oscillator across Pin 1 (input)
and Pin 7 (ground), of the mic connector.
(a) Set the frequency of the AF oscillator to 270Hz and
the output at a level that gives approximately 20
watts output on the RF wattmeter.
(b) Then vary the AF oscillator frequency to 2700Hz and
adjust C97 in the IF unit to obtain 20 watts on the
meter.