Tx Amplifier Circuits (Vhf Band); Apc Circuits (Vhf Band); Tx Amplifiers (Uhf Band); Apc Circuits (Uhf Band) - Icom ID-880H Service Manual

TX AMPLIFIER CIRCUITS (VHF BAND)

The output signal of VHF VCO (Q111, D145–148) is passed
through the LO SW (D155), LPF and ATT, then applied to
the drive AMP (Q25) via the limiter (D29), to obtain adequate
input level for the power AMP (power MOS-FET module;
IC3).
The amplifi ed TX signal is power-amplifi ed to 50 W (approx.;
25 W for [TPE] ver.) of output power (max.) by the power
AMP (IC3).
The power-amplified TX signal is passed through the LPF
which attenuates harmonic components to prescribed level,
then applied to the antenna connector via the power detector
(D39, 47, 1005), TX/RX SW (D59, 68, 75, 77) and two LPFs.

APC CIRCUITS (VHF BAND)

A portion of the TX signal from IC3 is rectifi ed at the power
detector (D39, 47, 1005), and converted into the DC voltage
which is in proportion to the RF power, and applied to the
operational amplifi er (IC4, pin 6). IC4 is an APC amplifi er for
both of V/UHF bands. The TX power setting voltage "PCON_
V" from the D/A converter (IC1) is applied to the pin 5 as
a reference. IC4 is rolled as a differential amplifier which
outputs voltage in inverse proportion to rectifi ed one.
When the TX power increased, the rectified voltage also
increased, that causes the decrease of output voltage of
differential amplifier. The decrease of output voltage of
differential amplifi er causes the drop of the gate voltage of
IC3, Thus the TX power maintained to keep stable level.
• TX AMPLIFIER AND APC CIRCUITS
VHF band TX signal ->
D155
LO SW
From the frequency synthesizer
circuits
UHF TX signal ->
D103
LO SW
D29
DRIVE
LPF ATT LIMITER
AMP
D25
Q22
PRE
LIMITER
DRIVE
HPF ATT

TX AMPLIFIERS (UHF BAND)

The output signal of UHF VCO (Q73, D87, 91, 92) is passed
through the LO SW (D103), HPF and ATT, then applied to
the pre-drive AMP (Q22). The amplifi ed TX signal is applied
to the drive AMP (Q26) via the limiter (D25) and amplifi ed to
obtain adequate input level for the power AMP (power MOS-
FET module; IC2).
The amplifi ed TX signal is power-amplifi ed to 50 W (approx.;
25 W for [TPE] ver.) of output power by the power AMP (IC2).
The power-amplified TX signal is passed through the LPF
which attenuates harmonic components to prescribed level,
then applied to the antenna connector via the power detector
(D42, 52, 1006), TX/RX SW (D30, 53, 61, 62, 177), HPF and
LPF.

APC CIRCUITS (UHF BAND)

A portion of the TX signal from IC2 is rectifi ed at the power
detector (D42, 52, 1006), and converted into the DC voltage
which is in proportion to the RF power, and applied to the
operational amplifi er (IC4, pin 2). IC4 is an APC amplifi er for
both of V/UHF bands. The TX power setting voltage "PCON_
U" from the D/A converter (IC1) is applied to the pin 3 as
a reference. IC4 is rolled as a differential amplifier which
outputs voltage in inverse proportion to rectifi ed one.
When the TX power increased, the rectified voltage also
increased, that causes the decrease of output voltage of
differential amplifier. The decrease of output voltage of
differential amplifi er causes the drop of the gate voltage of
IC2, Thus the TX power maintained to keep stable level.
D39,D47,D1005
IC3
Q25
PW R PWR
LPF
AM P
DET
IC2
Q26
PWR
DRIVE
LPF
AM P
AMP
IC4
APC
CTRL
T
PCON_U PCON_V
4 - 5
D59,68,75,77
TX/RX
LPF
SW
D42,52,1006 D30,53,61,62,177
PWR TX/RX
HPF
DET SW
To VHF RX circuits To UHF RX circuits
LPF