TK-3302
10
4. Transmitter System
■
Microphone Amplifi er
The signal from the microphone passes through the
IC308. When encoding DTMF, it is turned OFF for muting
the microphone input signal by IC308.
The signal passes through the Audio processor (IC308)
for the maximum deviation adjustment, and goes to the
VCO modulation input.
AGC
LPF
LPF
VCO
LPF
TCXO
MIC
DTMF
IC308
AQUA-L
IC306
MCU
QTVCO
QTTCXO
X1
Fig. 6 Microphone amplifi er
■
Drive and Final Amplifi er
The signal from the T/R switch (D10 is on) is amplifi ed by
the pre-drive (Q101 and Q102) and the drive amplifi er (Q103)
to 500mW.
The output of the drive amplifi er is amplifi ed by the RF
power amplifier (Q106) to 4.0W (1W when the power is
low). The output of the RF power amplifi er is then passed
through the harmonic fi lter (LPF) and antenna switch (D103)
and applied to the antenna terminal.
From
T/R SW
(D10)
Drive
AMP
RF
AMP
Pre-drive
AMP
Q102
Q101
Q103
RF power
AMP
Q106
ANT
SW
LPF
D103
ANT
VDD
VG
IC101
(1/2)
IC101
(2/2)
R120
R123
R126
+B
PCTV
(IC306)
5T
5T
VD
VG
Fig. 7 Drive and fi nal amplifi er and APC circuit
CIRCUIT DESCRIPTION
■
APC Circuit
The APC circuit always monitors the current flowing
through the drive amplifi er and RF power amplifi er (Q103
and Q106) and keeps a constant current.
The voltage drop at R120, R123 and R126 is caused by
the current flowing through the RF power amplifier and
drive amplifi er, and this voltage is applied to the differential
amplifi er IC101 (1/2).
IC101 (2/2) compares the output voltage of IC101 (1/2)
with the reference voltage from IC306. The output of IC101
(2/2) controls the VG of the RF power amplifier and drive
amplifi er to make both voltages the same.
The change of power high/low is carried out by the
change of the reference voltage.
■
Encode Signaling
• QT/DQT
QT/DQT data of the QTTCXO Line is output from pin 14
of the MCU. The signal passes through a low-pass CR fi lter
and goes to the TCXO (X1).
The QT/DQT data of the QTVCO Line is output from pin
15 of the MCU. The signal passes through a low pass CR fi l-
ter, mixes with the audio signal, and goes to the VCO modu-
lation input. TX deviation is adjusted by the MCU.
5. Power Supply
There are four 5V power supplies in the transceiver: 5M,
5C, 5R, and 5T. 5M for MCU is always output while the
power is on. 5M is always output, but turns off when the
power is turned off to prevent malfunction of the MCU.
5C is a common 5V and is output when SAVE is not set
to OFF.
5R is 5V for reception and output during reception.
5T is 5V for transmission and output during transmission.
6. Control Circuit
The control circuit consists of a MCU (IC306) and its
peripheral circuits. It controls the TX-RX unit. IC306 mainly
performs the following:
1) Switching between transmission and reception by the
PTT signal input.
2) Reading system, group, frequency, and program data
from the memory circuit.
3) Sending frequency program data to the PLL.
4) Controlling squelch on/off by the DC voltage from the
squelch circuit.
5) Controlling the audio mute circuit by the decode data in-
put.
6) Transmitting tone and encode data.
