Kenwood TK-2107, Руководство по обслуживанию

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7
TK-2107
TK-260 :K, K2
Fig. 4 PLL circuit
Fig. 6 Transmit audio QT/DQT
3) UNLOCK DETECTOR
If a pulse signal appears at the LD pin of IC1, an unlock
condition occurs, and the DC voltage obtained from D7, R6,
and C1 causes the voltage applied to the UL pin of the
microprocessor to go low. When the microprocessor detects
this condition, the transmitter is disabled, ignoring the push-to-
talk switch input signal. (See Fig.5)
4. Transmitter
1) Transmit audio
The modulation signal from the microphone is amplified by
IC500 (1/2), passes through a preemphasis circuit, and
amplified by the other IC500 (1/2) to perform IDC operation.
The signal then passes through a low-pass filter (splatter fiIter)
(Q501 and Q502) and cuts 3kHz and higher frequencies. The
resulting signal goes to the VCO through the VCO modulation
terminal for direct FM modulation. (See Fig. 6)
Fig. 5 Unlock detector circuit
IC1
LD
PLL IC
D7
C1
R6
5C
IC403
UL
MPU
PLL DATA
12.8MHz
REF OSC
I/M
I/N
PLL IC IC1
PHASE
COMPARATOR
CHARGE
PUMP
LPF
5kHz/6.25kHz
D1, 2
D3, 4
Q4
TX VCO
Q3
RX VCO
Q6
BUFF AMP
Q2
RF AMP
Q5, 7
T/R SW
5kHz/6.25kHz
MUTE
VR501
MAX
DEV
BALANCE
X1, IC1
D5, Q4
VCO
REFERENCE
OSC
(TCXO)
MIC
IC500 (1/2)
MIC
AMP
IC500 (1/2)
IDC
Q503
SW
PREEMPHASIS
Q501, 502
LPF
(SPLATTER FILTER)
IC403
TO
QT/DQT
2) VCO
The operating frequency is generated by Q4 in transmit
mode and Q3 in receive mode. The oscillator frequency is
controlled by applying the VCO control voltage, obtained from
the phase comparator, to the varactor diodes (D2 and D4 in
transmit mode and D1 and D3 in receive mode). The T/R pin is
CIRCUIT DESCRIPTION
set high in receive mode causing Q5 and Q7 to turn Q4 off,
and turn Q3 on . The T/R pin is set low in transmit mode. The
outputs from Q3 and Q4 are amplified by Q6 and sent to the
buffer amplifiers.
2) QT/DQT encoder
A necessary signal for QT/DQT encoding is generated by
IC403 and FM-modulated to the PLL reference signal. Since
the reference OSC does not modulate the loop characteristic
frequency or higher, modulation is performed at the VCO side
by adjusting the balance. (See Fig. 6)