Icom ID-51E User Manual page 15

TX AMP CIRCUITS (MAIN UNIT)
The TX signal is passed through the buffer (Q48) and ATT
(D20, D21), which controls the TX output power by the APC
AMP (IC14). The TX signal is sequentially amplifi ed by the
YGR (Q39), drive AMP (Q41) and power AMP (Q45).
• While operating on the VHF band
The amplifi ed TX signal is passed through the LPF (L501,
C511), ANT SW (D503 and D504), TX output power detector
(D512, D513) and two LPFs (L513, L515, L516, C547, C549,
C553, C555 and C556), before being applied to the antenna.
• While operating on the UHF band
The amplifi ed TX signal is passed through the HPF (L502,
L503, C507, C508, C510 and C512), ANT SW (D501), TX
output power detectors (D505 and D509) and two LPFs
(L507, C524, C526, C529, and L511, C536, C539) and HPF
(L512, L514, C545, C548, C550, C551 and C554), before be-
ing applied to the antenna.
• TX AMP AND APC CIRCUITS
Q48
D14 D20,D21
LO
ATT
BUFF
SW
IC14B
APC
CTRL
PSET
Q43
MUTE
SW
TXMUTE
Q39 Q41 Q45
YGR DRIVE PWR
AMP AMP AMP
MAIN UNIT
APC CIRCUITS (MAIN UNIT)
The voltage produced at the LPFs (VHF band; L513, L515,
L516, C547, C549, C553,C555 and C556, UHF band; L507,
C524, C526 and C529) is rectifi ed by the diodes (VHF band;
D512 and D513, UHF band; D505 and D509), and it is used
as the TX power sensing voltage.
The voltage is applied to the APC AMP (IC14B, pin 6), and
the output voltage controls the bias voltages of the ATT (D20
and D21) to keep the TX output power constant.
D501
D508
D510
ANT
HPF LPF
SW
D505,D509
PWR
DET
PWR
DET
D512,D513
D503,D504
D506,D903
ANT
LPF LPF
SW
Receive circuit (UHF band) ->
Receive circuit (VHF band) ->
4 - 6
ANTENNA
TX:400.000M~479.000MHz
RX:380.000M~479.000MHz
LPF HPF
TX:136.000M~174.000MHz
RX:108.000M~174.000MHz
LPF