Kirisun PT8000, Руководство по обслуживанию

Страница: 7 / 32

PT8000 Service Manual
5
4.5 Audio Processing Circuit
Figure 4.5 Audio Processing
MIC signal processing:
Voice signal from MIC is sent to IC13A for amplification
(IC13A, D32, Q32 and other components form the AGC circuit to
improve the dynamic range of the circuit). Then the resulting
signal is pre-emphasized by C322 and R267 and goes to the IDC
circuit consists of IC13B. After being limited, the signal is
switched into wideband or narrowband in Q30 and then passes
through two low pass circuits of IC13C and IC13D to remove
signals above 3000Hz. Then the filtered signal is sent to VR2 to
adjust the deviation, and is modulated by D8, and then is sent to
Tx VCO.
Rx audio signal processing:
Voice signal from IC6 is divided into two parts. One branch of
the signal is routed to the low pass circuit consists of IC8, where it
is amplified and filtered (to remove the voice signal) to obtain
more purified CTCSS/DCS signal, which is then sent to MCU for
processing. The other branch of the signal goes to IC9. After being
amplified by IC9C (Q29 is the gain switching circuit which is
used to switch volume between wideband and narrowband), the
signal is divided into two branches again. One branch is sent to
the 2-tone shaping circuit consists of IC10, where it is shaped into
better square wave signal, and then is sent to MCU to judge the
2-tone signal; the other branch passes through the high pass circuit
consists of IC6D to remove the sub-audio signal and passes
through the de-emphasis circuit consists of R173 and C245. Then
the de-emphasized signal is passed through the low pass circuit
consists of IC9A and IC9D and the high pass circuit consists of
Q26. After that, the resulting signal goes to the volume switch
where the signal volume will be adjusted. After being amplified in
IC7, the signal will be output to drive the speaker.
Impedance of the speaker: 16 Ω
Note:
* Any terminal of the speaker should not be grounded.
* The emergency alarm sound has no volume limit.
4.6 Power Supply:
The radio uses 13.8V battery, and the Tx power amplification
circuit (IC1) and Rx audio power amplifier (IC7) directly adopt
the battery for power supply.
IC17: 5V, LDO, micropower regulator, which supplies power for
MCU, IF processing unit and frequency synthesizer etc.
IC16: 8V, LDO, micropower regulator.
Q38: 8T switch, which is controlled by MCU.
8T: Supplies power for front end of transmitter.
Q40: 8R switch, which is controlled by MCU.
8R: Supplies power for RF amplifier and mixer of the receiver.
4.7 MCU Unit
MCU unit controls the operation of each unit of the radio so
that all functions can be realized.
Communicate with external PC.
Access the status data of the radio.
Control the PLL to generate Rx and Tx local oscillator
frequencies.
Obtain status parameters of current channel.
Control status of LED indicator.
Control power supply for each unit.
Check the actions of each functional key.
Generate CTCSS signal.
Generate DCS signal.
Generate power control signal.
Perform CTCSS decoding.
Perform DCS decoding.
Test and control the squelch.
Control content of voice alert.
Memory (E
2
PROM, AT24C08)
The memory is stored with channel data, CTCSS/DCS data,
other data for function setting, and parameter adjusting data.
CTCSS/DCS signal encoding and decoding:
CTCSS/DCS signal (output from pin12, PWM wave)
generated by MCU is balanced and adjusted by VR1. Then the
resulting signal is sent to VCO and TCXO respectively for
modulation.
CTCSS/DCS signal from the receiver is sent to MCU for
decoding. MCU checks if the received CTCSS/DCS signal
matches the preset value of the radio, and determines whether to
open the speaker or not.
SPEAKER
IC6
Q33
SW
AF POWER AMP
IC7
AF OUT
MUTE
TDA1519C
IC8A IC8B IC8C IC8D
AMP LP LP AMP
CTCSS/DCS
MIC
IC9C IC9B IC9A IC9D
AMP HP LP LP
HP
Q26
8R
IC10B IC10A
HP
AMP
2T
IC5
DTMF
DECODER
D0
D1
D2
D3
DV
J1 SPK
IC13D IC13A IC13B IC13C
LP LP IDC AMP
MOD
VR1
10K