Drive And Power Amplifier Circuits; Alc Circuit; Apc Circuit - Icom IC-7000 Service Manual

3-2-9 DRIVE AND POWER AMPLIFIER CIRCUITS

(PA AND DRIVER UNITS)
The drive and power amplifier circuits amplify the RF signal
from the RF circuit (MAIN unit) to obtain 100 W of RF output
power for the HF/50 MHz bands, 50 W for the VHF band
and 35 W for the UHF band.
The RF signal from the MAIN unit is applied to the pre drive
amplifiers (PA unit; Q101, Q102) after passed through the
attenuator (PA unit; R101–R103). The amplified signal is
applied to the drive amplifier (DRIVER unit; Q504) to amplify
a level needed for the power amplifiers.
The amplified HF/50 MHz bands signal from the drive ampli-
fier is amplified at the power amplifiers (PA unit; Q301,
Q302) to obtain a stable 100 W of RF output power. The
power amplified signal is passed through the TX/RX switch
(RL801), one of the 7 low-pass filters, APC detector (PA
unit; D961, D962) and then applied to the [ANT1] connector
(CHASSIS; J1).
The amplified VHF RF signal from the drive amplifier is
amplified at the power amplifier (Q501) to obtain a stable
50 W of RF output power. The power amplified signals are
applied to the low-pass filter, APC detector (D501–D504),
TX/RX switch (D506, D510), low-pass filters (L506, L508,
L510, L601–L603, C516, C519, C521, C601, C602) and
[ANT2] connector (CHASSIS; J2).
The amplified UHF RF signal from the drive amplifier is
amplified at the power amplifier (Q401) to obtain a stable
35 W of RF output power. The power amplified signal is
applied to the low-pass filter, APC detector (D401–D404),
TX/RX switch (D406, D407), high-pass filter (L413, L414,
C428, C429, C431, C433), low-pass filter (L601–L603,
C601, C602) and [ANT2] connector (CHASSIS; J2).
3-2-10 ALC CIRCUIT (MAIN UNIT)
The ALC (Automatic Level Control) circuit reduces the gain
of IF amplifiers in order for the transceiver to output a con-
stant RF power set by the RF power setting even when the
supplied voltage shifts, etc.
The HF/50 MHz power amplified signal from the power
amplifiers (PA unit; Q301, Q302) is detected at the APC
detector (PA unit; D961). The detected voltage is applied
to the buffer amplifier (PA unit; IC960, pins 5, 7) and then
applied to the MAIN unit as the "HFOR" voltage.

• ALC CIRCUIT

3rd mixer 2nd mixer
TX
IF
signals
Q901
1st mixer
Crystal
IF
BPF
Q701 FI601
ALC amplifier
ALC
1
IC1601
The VHF and UHF RF power amplified signal from the
power amplifiers (PA unit; Q401, Q501) are detected at the
APC detectors (PA unit; D401, D404, D501, D504) respec-
tively. The detected voltages ("VFOR" and "UFOR") are
combined to "VUFOR" voltage and then applied to the MAIN
unit.
The "HFOR" and "VUFOR" voltages are combined to the
"FORL" voltage and then applied to the ALC amplifier
(IC1601, pins 1, 2). The "POCV" voltage from the D/A con-
verter (IC2155, pin 19) via the buffer amplifier (IC2101,
pins 5, 7), determined by the RF power setting, is applied to
the ALC amplifier (IC1601, pin 3) as the reference voltage.
When the "FORL" voltage exceeds the "POCV" voltage, ALC
bias voltage from IC1601 (pin 1) controls the IF amplifiers
(Q701, Q901). This adjusts the output power to the level
determined by the RF power setting until the "FORL" and
"POCV" voltages are equalized.
In AM mode, IC1601 functions as an averaging ALC ampli-
fier with Q1601. The AM switch (Q1602) is turn ON and
shifts the "POCV" voltage to adjust the TX output power for
the AM mode (maximum; 40 W for HF/50 MHz bands, 20 W
for VHF band, 14 W for UHF band).
The ALC bias voltage from IC1601 is also applied to the
main CPU (LOGIC unit; IC1302, pin 115) as the "ALCL" volt-
age for ALC meter indication.
The external ALC input (negative voltage) from the [ACC]
socket (pin 6) is converted to a positive voltage at D1609
and is applied to the buffer amplifier (Q1604). External ALC
operation is identical to that of the internal ALC.
3-2-11 APC CIRCUIT (MAIN UNIT)
The APC (Automatic Power Control) circuit protects the
power amplifiers on the PA unit from high SWR and exces-
sive current.
The reflected wave signal appears and increases on the
antenna connector when the antenna is mismatched.
The HF/50 MHz reflected signal level is detected at D962 (PA
unit), and is amplified at the buffer amplifier (PA unit; IC960,
pins 1, 3) and applied to the ALC amplifier (IC1601, pins 8, 9)
as the "HREF" voltage.
HF/50 MHz
AMP PA
HPFs
145 MHz
DRIVER
BPF PA
UNIT
430 MHz
PA
2
ALC
3 - 6
ANT1 ANT2
PA UNIT
APC
LPFs
DET
APC
DET
APC
DET