Icom IC-F50V

4 - 5
TRANSMIT AMPLIFIERS
The transmit amplifiers consist several RF amplifiers (pre-
driver, driver, power), and amplify the TX VCO output to the
transmit output level.
The TX VCO output is applied to the pre-drive amplifi er
via
the TX/RX switch. The amplified TX signal is amplified by
drive amplifier, then power-amplified by the power amplifier
to obtain 5 W (max.) of TX output power.
The power-amplified TX signal is passed through the LPFs
(as a harmonic filter), ANT SW (TX), and another LPF, then
applied to the antenna.
APC CIRCUIT
The APC (Automatic Power Control) circuit stabilizes
transmit output power to prevent transmit output power level
change which is caused by load mismatching or heat effect,
etc. The APC circuit also selects transmit output power from
high, middle and low power.
A portion of the TX signal is rectifi ed by the power detector
to be converted into DC voltage which is in proportion to the
transmit output power level. The detected voltage is applied
to the comparator. The transmit power setting voltage is ap-
plied to another input terminal as the reference voltage.
The comparator compares the detected voltage and refer-
ence voltage, and the difference of voltage is output. The
output voltage controls the bias of the TX amplifiers to re-
duce/increase the gain of these amplifi ers for stable transmit
output power.
The change of transmit power is carried out by changing
reference voltage.
C72
R65
C83
R59
Q7
C99
0.001
L20
C93
TX
MP 1
2681
C302
C78
C2
C81
C91
To ANT
C98
L18
C80
L16
Q9
C292
C15
C73
L2
C101
L1
C308
R61
Q8
C89
C10
R6
C6
C9
C77
R1
D1
C95
C88
R58
C79
C108
0.01
R69
C5
R55
C12
R67
R63
IC2
1
2
3
4
5
C1
R8
C7
R5
R52
R62
L19
L17
C106
D15
R57
C11
R10
C74
L15
C87
C291
R53
0
0
R54
R4
R68
C84
R51
C90
C94
C76
0.1
D14
C8
C96
R2
C4
D2
L4
D25
C85
EP2
R7
C13
C82
C97
C92
C3
R9
C86
L3
R3
T2
TMUT
LPF
LPF
R
APC CIRCUIT
COMPARATOR
TX/RX
SW
LPF
PWR
AMP
DRIVE
AMP
Pre-
DRIVE
ANT SW
(TX)
TX POWER
DETECTOR
L14
C324
C183
C323
C49
LPF
• TRANSMIT AMPLIFIERS AND APC CIRCUIT