Kenwood TK-863G, Руководство по обслуживанию, Страница: 19 / 56

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TK-863G
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Wide/Narrow Changeover Circuit
The W/N port (pin 4) of the shift register (IC510) is used
to switch between ceramic filters. When the W/N port is
high, Q4 turns on and the ceramic filter SW diode (D8, D10)
CF1 turns on to receive a Narrow signal. At the same time,
Q35 turns on and one of the filters is selected so that the
wide and narrow audio output levels are equal.
When the W/N port is low, Q3 turns on and the ceramic
filter SW diode (D8, D10) CF2 turns on to receive a Wide
signal.
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AF Signal System
The detection signal (DEO) from the TX-RX unit (A/2)
goes to the audio processor (IC508) of the TX-RX unit (B/2).
The signal passes through a filter in the audio processor to
adjust the gain, and is output to IC507. IC507 sums the AF
signal and the DTMF signal, BEEP signal and returns the re-
sulting signal to the TX-RX unit. The signal (AFO) sent to the
TX-RX unit (A/2) is input to the D/A converter (IC6). The AFO
output level is adjusted by the D/A converter. The signal
output from the D/A converter is input to the audio power
amplifier (IC13). The AF signal from IC13 switches between
the internal speaker and speaker jack (J1) output.
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Squelch Circuit
The detection output from the FM IF IC (IC5) passes
through a band-pass filter and a noise amplifier (Q10) in the
TX-RX unit (B/2) to detect noise. A voltage is applied to the
CPU (IC502). The CPU controls squelch according to the
voltage (ASQ) level. The signal from the RSSI pin of IC5 is
monitored. The electric field strength of the receive signal
can be known before the ASQ voltage is input to the CPU,
and the scan stop speed is improved.
FIg. 4 AF signal system
Fig. 5 Squelch circuit
CIRCUIT DESCRIPTION
Fig. 3 Wide/Narrow changeover circuit
CF1
(Narrow)
CF2
(Wide)
IFI
MXO
IC5
IF system
AFO
DET
OUT
C70
C72
C53
R19
R23
R46
R32
R30 R39
R38
+
+
Q35
8RC
Q37
R59
W/N
IC510 4pin
Wide : L
Narrow : H
C51
D8 D10
Q3
5C
Q4
Wide : H
Narrow : L
AUDIO
PROCE.
SUM
AMP
D/A
CONV.
IC508 IC507 IC6
AF PA
IC13 SP
DTMF
AFO
DEO
TX-RX UNIT (B/2)
Q10
NOISE AMP D11 IC4 IC5 IC502
AF
RSSI
BPF DET
CPU
IF
SYSTEM
TX-RX UNIT (B/2)
ASQ
RSSI
PLL Frequency Synthesizer
The PLL circuit generates the first local oscillator signal
for reception and the RF signal for transmission.
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PLL
The VCO output is doubled by Q9 and then sent to the
PLL IC (IC3). The frequency step of the PLL circuit is 10 or
12.5kHz. A 16.8MHz reference oscillator signal is divided at
IC3 by a fixed counter to produce the 10 or 12.5kHz refer-
ence frequency. The voltage controlled oscillator (VCO) out-
put signal is buffer amplified by Q106 (Sub-unit), then di-
vided in IC3 by a dual-module programmable counter. The
divided signal is compared in phase with the 10 or 12.5kHz
reference signal in the phase comparator in IC3. The output
signal from the phase comparator is filtered through a low-
pass filter and passed to the VCO to control the oscillator
frequency. (See Fig. 6)
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VCO
The TK-863G has VCO in a Sub-unit (A1) housed in a solid
shielded case and connected to the TX-RX unit (A/2) through
CN101.
The operating frequency is generated by Q103 in trans-
mit mode and Q101 in receive mode. The oscillator fre-
quency is controlled by applying the VCO control voltage,
obtained from the phase comparator, to the varactor diodes
(D102 and D104 in transmit mode and D101 and D103 in
receive mode). The RX (ST) pin is set low in receive mode
causing Q102 to turn Q103 off, and turn Q101 on. The RX
(ST) pin is set low in transmit mode. The outputs from Q101
and Q103 are amplified by Q106 and sent to the buffer am-
plifiers.