JETStream JT220M, Руководство по обслуживанию

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JT220M
6
CPU
CS
U2
LCD
U3
LCD
COM0~COM3
SEG0~SEG27
driver
WR
DI
Q6,Q7
SW
8C
D5
P12
BLUE
CIRCUIT DESCRIPTION
Fig. 12 Display circuit

Encode
The CTCSS and DCS signal that is output from CPU(U2) of P31 pass through two-way digital switches
and buffer amplifier(U8A) to amplify. The DTMF signal that is output from DTMF encoder passes through
buffer amplifier (U8A) to amplify, and amplified by the other U504 (B/4) to perform IDC operation. The
signal then passes through a low-pass filter (splatter filter) U504 (C/4and D/4) and cuts 3kHz and higher
frequencies. and the resulting signal goes to the D/A converter (U505).
The D/A converter (U505) adjusts the balance between the MOD and CTCSS/DCS levels. Signal of
CTCSS/DCS port is summed with MOD and the resulting signal goes to the VCO. This signal is applied to
a varicap diode in the VCO for direct FM modulation. (See Fig. 13.)
Fig. 13 Encode circuit

Decode
CTCSS/DCS/ DTMF
The signal from (AFWN) entering into AF signal and higher audio frequencies output by pin 1 of U501: A
are cut by low-pass filter U503 and amplified. then led to pin 42 of CPU. The input signal is compared with
the programmed tone frequency code in the CPU. The squelch will open when they match.
The signal (DTMF-DET) goes to P27 (pin 43) of CPU (U2). The DTMF input signal from the DTMF-DET
goes to compared U8B. The compared signal goes to the CPU for processing and be decoded within the
CPU (U2). (See Fig. 14.)
Fig. 14 Decode circuit
2-CHANNEL
DIGITAL SW
D/A
U505
U2
CPU
VCO
X200
TCXO
U205
PLL
DTMF
DCS/CTCSS
U4
DTMF
Encode
BUFFER
AMP
U8A
U7
TCXO
MOD
VCO MOD
AFWN LPF
CPU
U503
U2
FILTER
BUFFER AMP
U501D
U8B
COMPARATOR
U501B/U502
LPF/HPF
FILTER
DTMF-DET