PT6808 Service Manual
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EEPPOM
Note: EEPPOM keeps tuning data (quadrature and noise suppression circuit). If the EEPPOM is
changed, the mobile radio needs to be adjusted.
4.7 Signaling circuit
4.7.1 Encoding
- Low speed data (QT and DQT)
Pin 20 of IC13 outputs low speed data. The output signal passes through low pass ceramic filter,
and then comes to summation amplifier (IC7 1/2). Then the signal mixes with the audio signal,
passes through digital/analog conversion to make BAL adjustment, and then comes to VCO (AI) and
TCXO (XI) to modulate.
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High speed data (DTMF)
Pin 2 of IC19 outputs high speed data. The output signal passes through low pass ceramic filter
consisted of by IC 10, and supplies TX HSD audio and RX HSD audio. TX HSD error adjusted by
microprocessor comes to digital/analog conversion (IC8), and then supplies to audio processor (IC
13).
Then the signal mixes with audio signal, and then comes to VCO and TCXO. RX HSD passes
through summation amplifier (IC7 2/2). Digital/analog conversion (IC8) is controlled and amplified
by the audio power, and then comes to the speaker.
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FFSK
ESN adopts 1200bps FFSK signal. Pin 19 of IC13 outputs FFSK signal. The signal passes
through digital/analog conversion (IC8) for FFSK deviation adjustment, and then comes to VCO. If
programming FFSK, the input signal of MIC is mute.
4.7.2 Decoding
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Low speed data (QT and DQT)
The modulated signal coming from IF chip (IC 12) is amplified by IC4 (2/2), and then is input to
pin 11 of IC13.
IC13 is digitalized, and performs the functions such as recover DC and decode signal.
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FFSK
FFSK input signal coming from IF is amplified by IC4 (1/2), and then comes to pin 11 of IC13.
The signal is then demodulated by FFSK demodulator of IC13.
4.8 Power supply circuit
