TK-8100
25
■
Wide/Narrow Switching Circuit
The Wide port (pin 65) and Narrow port (pin 64) of the CPU
is used to switch between ceramic filters. When the Wide
port is high, the ceramic filter SW diodes (D303, D302) cause
CF301 to turn on to receive a Wide signal.
When the Narrow port is high, the ceramic filter SW diodes
(D303, D302) cause CF302 to turn on to receive a Narrow sig-
nal.
■
AF Signal Circuit
The detection signal from IF IC (IC301) goes to D/A con-
verter (IC161) to adjust the gain and is output to AF filter
(IC251) for characterizing the signal. The AF signal output
from IC251 and the DTMF signal, BEEP signal are summed
and the resulting signal goes to the D/A converter (IC161).
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 (IC252). The AF signal from IC252 switches
between the internal speaker and speaker jack (J1) output.
■
Squelch Circuit
The detection output from the FM IF IC (IC301) passes
through a noise amplifier (Q301) to detect noise. A voltage is
applied to the CPU (IC101). The CPU controls squelch ac-
cording to the voltage (SQIN) level. The signal from the RSSI
pin of IC301 is monitored. The electric field strength of the
receive signal can be known before the SQIN voltage is input
to the CPU, and the scan stop speed is improved.
Narrow
IC101 64pin
IF_IN
MIX_O
IC301
IF System
CF302
(Narrow)
CF301
(Wide)
R320
R319
R317
R318
D303
D302
Wide
IC6 65pin
AF
Filter
D/A
CONV.
D/A
CONV.
IC161
IC251
IC161
W/NO
(EVOL2)
AF PA
IC252
SP
IF IC
IC301
Q301
NOISE AMP
D301
IC301
IC101
AFO
RSSI
DET
CPU
IF
SYSTEM
SQIN
RSSI
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Fig. 5 Squelch circuit /
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CIRCUIT DESCRIPTION /
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