Kenwood TM-471A Service Manual page 7

■ Transmission Signals
Transmission modulation signals enter from PKD of the
data terminal (CN2). The path to the modulation depends on
whether communications are 1200bps or 9600bps mode.
For 1200bps mode, the transmission modulation signals
from single analog switch (IC204) pass through MIC amplifier
(IC201,202) and summing amplifier (IC203), and go to VCO
(X401) through D/A converter (IC161).
For 9600bps mode, the transmission modulation signals
from single analog switch (IC205) pass through summing
amplifier (IC303), go to TCXO (X401) and VCO through D/A
converter (IC161). (See Fig. 17.)
■ Reception Signals
PR9 is the 9600bps data communications reception out-
put. It outputs the FM detection circuit output through an AF
filter (IC251). These signals are always output whether the
squelch is open or closed.
CN2
PKD
PR9
PR1
PKS
SQC
CIRCUIT DESCRIPTION
IC204
Analog
switch
1200bps
76
IC101
CPU
75
9600bps
IC205
Analog
switch
IC251
Q252
AF filter
Mute SW
D6
D5
Fog. 17 Data terminal and peripheral circuits
PR1 is the 1200bps data communications reception out-
put. It outputs the FM detection circuit output through an AF
filter (IC251). Output is controlled with the mute switch
(Q252) according to whether squelch is open or closed. (See
Fig. 17.)
■ Squelch Signal Output Circuit
The squelch circuits is input to the TNC to prevents con-
flicts from occurring between simultaneous receive mode
and transmit mode traffic during packet communications
(only during 1200bps). The signal is output from pin 29 of
IC101 to the data terminal. The logic is as shown in the table
below.
SQC terminal output
CN2
IC201,202
MIC amp
IC203 VCO, TCXO,
Sum amp D/A converter
D/A converter
PKS (CPU) pin 30
SQC (CPU) pin 29
TM-471A
L : SQ CLOSE
H : SQ BUSY
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