TK-3301
8
■
Receive Signaling
• QT/DQT
The output signal from FM IC (IC201) enters the MCU
(IC306) through IC308. IC306 determines whether the QT or
DQT matches the preset value, and controls the SP MUTE
and the speaker output sounds according to the squelch re-
sults.
3. PLL Frequency Synthesizer
The PLL circuit generates the fi rst local oscillator signal
for reception and the RF signal for transmission.
■
PLL
The frequency step of the PLL circuit is 5 or 6.25kHz.
A 12.8MHz reference oscillator signal is divided at IC1 by
a fi xed counter to produce an oscillator (VCO) output signal
which is buffer amplifi ed by Q3 then divided in IC1 by a pro-
grammable counter. The divided signal is compared in phase
with the 5 or 6.25kHz reference signal from the phase com-
parator in IC1. The output signal from the phase comparator
is fi ltered through a low-pass fi lter and passed to the VCO
to control the oscillator frequency. (See Fig. 5)
■
VCO
The operating frequency is generated by Q5 in transmit
mode and receive mode. The oscillator frequency is con-
trolled by applying the VCO control voltage, obtained from
the phase comparator, to the varactor diodes (D4 and D8).
The outputs from Q5 is amplifi ed by Q9 and sent to the
RF amplifi ers.
■
Unlock Detector
If a pulse signal appears at the LD pin of IC1, an unlock
condition occurs, and the DC voltage obtained from C4 and
Q1 causes the voltage applied to the MCU to go low. When
the MCU detects this condition, the transmitter is disabled,
ignoring the push-to-talk switch input signal.
D4,8
Q5
VCO
Q9
BUFF AMP
Q3
BUFFER
Q11
RF AMP
LPF
LPF
REF OSC
1/M
1/N
Phase
comparator
Charge
pump
5 or 6.25kHz
5 or 6.25kHz
PLL DATA
X1
12.8MHz
IC1
PLL IC
Fig. 4 PLL circuit
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. 5 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).
The output of the drive amplifi er is amplifi ed by the RF
power amplifier (Q106) to 0.5W. 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. 6 Drive and fi nal amplifi er and APC circuit
■
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
CIRCUIT DESCRIPTION
