Transmitter System; Microphone Amplifier; Vox; Drive And Final Amplifier - Kenwood TK-2180 Service Manual

4. Transmitter System

4-1. Microphone amplifier

The signal from the internal microphone goes through the
mute switch (Q614).
When the SP-MIC is not attached, the microphone switch-
ing terminal (MSW) on the universal connector becomes
High, and mute switch (Q614) is turned on. When the SP-
MIC is attached, MSW is connected to GND at inside of SP-
MIC. For this reason, Q614 is turned off, the internal micro-
phone is muted, and only the input of the external micro-
phone is supplied to the microphone amplifier.
The signal from microphone goes through D/A converter
(IC605), mute switch (Q610), and amplified by IC608 (1/2) and
limited by AGC circuit composed of D601, D602, Q606 and
Q607. IC607 is composed of high-pass filter, low-pass filter
and pre-emphasis/IDC circuit.
The signal passes through the D/A converter (IC605) for
the maximum deviation adjustment, and enters the summing
amplifier consisting of IC600 (2/2), and is mixed with the low
speed data from the CPU (IC502).
EXT.
MIC
MIC Q614 IC605 Q610
SW VOL SW
MMUTE
Q616
(2/2)
MSW
IC600
IC605 (2/2)
SUM
D/A
O2
I2
AMP
LSD
OUT
Fig. 7 Microphone amplifier
CIRCUIT DESCRIPTION
IC608
(1/2)
IC607
AMP AQUA-L
AGC
D601,602
Q606,607
VCO
IC605 IC602 X1
BUFF
D/A TCXO
I1 O1
AMP
Q101 Q102
From
Pre-DRIVE DRIVE
T/R SW
AMP AMP
(D100)
R130
+B
R127
R125
REF
VOL
(IC502)
Fig. 8 Drive and final amplifier and APC circuit
The output signal from the summing amplifier goes to the
VCO modulation input. The other output signal from the
summing amplifier passes through the D/A converter (IC605)
again for the BAL adjustment, and the buffer amplifier
(IC602), and goes to the TCXO modulation input.

4-2. VOX

The IC608 (2/2) amplify the audio signal captured in the
microphone, and then the signal is converted into the DC
voltage D603 rectifies.
The DC voltage activates the CPU (IC502), and the VOX
starts.

4-3. Drive and Final amplifier

The signal from the T/R switch (D100 is on) is amplified by
drive amplifier (Q101 and Q102) to +15~17dBm.
The output of the drive amplifier is amplified by the RF
power amplifier (Q105) to 5.0W (1W when the power is low).
The RF power amplifier is MOS FET. The output of the RF
power amplifier is then passed through the harmonic filter
(LPF) and antenna switch (D106, D107 are on) and applied to
the antenna terminal.
4-4. APC circuit
The APC circuit always monitors the current flowing
through the RF power amplifier (Q105) and keeps a constant
current. The voltage drop at R125, R127 and R130 is caused
by the current flowing through the RF power amplifier and
this voltage is applied to the differential amplifier (IC100 1/2).
IC100 (2/2) compares the output voltage of IC100 (1/2)
with the reference voltage from IC502, and the output of
IC100 (2/2) controls the VGG of Q101, Q102 and Q105 to
make the both voltages to same voltage.
The change of power high/low is carried out by the change
of the reference voltage. Q106, Q107 and Q108 are turned
on and Q104 is turned off in transmit and the APC circuit is
active.
Q105 D106,107
RF POWER ANT
LPF
AMP SW
VDD VGG
IC100 IC100
(1/2) (2/2)
TK-2180
ANT
9