Panasonic KX-TC1881B, Service Manual

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10.4. Signal Flowchart in the Whole System
Reception
CN101 (LINE 1/2) or CN201 (LINE 2) of the base unit is connected to the TEL line, and the signal
is input through the bridge diode D101 (LINE 1), D201 (LINE 2). While talking the relay (Q101 for
LINE 1, Q201 for LINE 2) is turned ON and amplified at the amplifiers Q162 and Q164 (LINE 1),
IC250, IC251, Q264 (LINE 2), then led to DSP (IC501). DSP generates ADPCM signal. The ADPCM
signal is input to RFIC (IC101) of RF UNIT, and is mixed with pseudo random noise code (PN
code) to spread the spectrum. RFIC outputs FSK modulated RF signal. The RF signal is passed
through the balun (T101) and filter (F102) to be transmitted from the antenna. As for the handset,
RF signal from the antenna is input to RFIC passing through filter (F102) and the balun (T101) to
perform the de-spread, then input to DSP (IC201). DSP performs ADPCM decoding to convert
the signal into the voice signal, then it is output to the speaker.
Transmission
The voice signal input from the microphone is led to DSP (IC201). The DSP generates ADPCM
signal. As well as the reception, it is converted into the RF signal by RFIC (IC101). Passing
through the balun (T101) and filter (F102), it is transmitted from the antenna. As for the base
unit, RF signal from the antenna is input to RFIC (IC101) passing through filter (F102) and the
balum (T101) to perform the de-spread, then input to DSP (IC501). DSP performs ADPCM
decoding to convert the signal into the voice signal. The voice signal is amplified at the TX
amplifier (Q161 for LINE 1, Q261 for LINE 2), then output to the TEL line CN101 (LINE 1), CN201
(LINE 2) through the relay (Q101 for LINE 1, Q201 for LINE 2) and bridge (D101 for LINE 1, D201
for LINE 2).
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