Transmitter; Dsc Encoder/ Decoder - Standard Horizon MATRIX GX3000S Service Manual

Circuit Description
varactor diode D1013 (1SV325). The TX & SUB VCO out-
put passes through buffer amplifier Q1028 (2SC5006) to
obtain stable output. The TX & SUB VCO output is passed
through another buffer amplifier Q1024 (2SC3356-R25)
and diode switch D1007 (DAN235U) to the sub 1st mixer
which is composed of balun transformers (T1004, T1005,
and T1006) and quadrate FETs Q1026, Q1027, Q1029, and
Q1030 (all 2SK520-K41) during receive, and to drive am-
plifiers Q1020 (2SC3356-R25) for transmit. The DC sup-
ply for the TX & SUB VCO is regulated by Q1022
(2SC4154E).

Transmitter

Voice audio from the microphone is delivered to the AF
Unit. After passing through microphone amplifier Q2020
(LM2902PW), a pre-emphasis network, limiter (IDC: in-
stantaneous deviation control), and low-pass filter net-
work, the audio is adjusted for optimum deviation level
and delivered to the next stage.
Voice or DSC (Digital Selective Calling) encode signal in-
puts from the low-pass filter network Q2020 (LM2902PW)
is applied to the TX & SUB VCO Q1031 (2SK520-K4) and
varactor diode D1014, D1015, D1016, & D1017 (all
1SV286), which oscillates the fundamental transmit fre-
quency with direct frequency-modulation using varactor
diode D1013 (1SV325). The modulated signal is ampli-
fied by the buffer amplifier Q1028 (2SC5006) and Q1024
(2SC3356-R25), then passed through the diode switch
D1007 (DAN235U) to drive amplifiers Q1020 (2SC3356-
R 2 5 ) a n d R F p o w e r a m p l i f i e r m o d u l e Q 1 0 0 1
(RA35H1516M).
The RF energy then passes through antenna switch D1006
(XB15A30B) and low-pass filter (LPF) consisting of coils
L1009 and L1010 and capacitors C1010, C1017, & C1038,
and finally to the antenna connector.
RF output power from the RF power amplifier module
Q1001 (RA35H1516M) is sampled by C1023 and C1032
and is rectified by D1004 (1SS321). The resulting DC is
fed through Automatic Power Controllers Q1002
(LM2904PW) to RF power amplifier module Q1001
(RA35H1516M), thus providing positive control of the
power output.
Generation of spurious products by the transmitter is min-
imized by the fundamental carrier frequency being equal
to the final transmitting frequency, modulated directly in
the transmit VCO. Additional harmonic suppression is
provided by a low-pass filter consisting of coils and ca-
pacitors, resulting in more than 70 dB of harmonic sup-
pression prior to delivery of the RF energy to the antenna.
8

DSC Encoder/ Decoder

Encoder
The DSC (Digital Selective Calling) encode signal which
D / A c o n v e r t e d i n t h e 1 6 - b i t M P U I C Q 3 0 0 4
(M30626FHPGP) on the CNTL Unit is fed through the
low-pass filter Q2020 (LM2902PW) on the AF Unit to the
TX & SUB VCO Q1031 (2SK520-K41) on the RF Unit.
Decoder
Incoming the receiving DSC code on the CH70 from the
antenna connector are passed through a SUB-RX RF am-
plifier Q1015 (3SK294) to the bandpass filter consisting
of coils L1006, L1007, & L1008 and capacitors C1122,
C1127, C1132, C1139, C1146, C1154, and C1159, then the
filtered signal deliver to the sub 1st mixer which is com-
posed of balun transformers (T1004, T1005, and T1006)
and quadrate FETs Q1026, Q1027, Q1029, and Q1030 (all
2SK520-K41).
Buffered output from the TX & SUB VCO Q1031 (2SK520-
K41) is amplified by Q1028 (2SC3356-R25) and Q1024
(2SC5006) and bandpass filtered by coils L1028 & L1029
and capacitors C1145, C1148, C1153, C1155, & C1160, to
provide a pure 1st local signal (134.225 MHz) for delivery
to the sub 1st mixer.
The 22.3 MHz 1st mixer product then passes through
monolithic crystal filters XF1001 and XF1002 (±6.5 kHz
BW) and buffer amplifier Q1043 and Q1044 (both
2SC4400-3), then deliver to the SUB-RX FM IF subsystem
IC Q1050 (TA31136FN). This IC contains the 2nd mixer,
2nd local oscillator, limiter amplifier, FM detector, noise
amplifier, and squelch gates.
The 2nd local is produced by crystal X1002 (21.850 MHz)
then deliver to the 2nd mixer in the SUB-RX FM IF sub-
system IC Q1050 (TA31136FN). The 1st IF is converted to
450 kHz by the 2nd mixer and stripped of unwanted com-
ponents by ceramic filter CF1002.
Filtered signal from the ceramic filter CF1002 is applied
to the limiter amplifier in the SUB-RX FM IF subsystem
IC Q1050 (TA31136FN), and then demodulate by the FM
detector in the SUB-RX FM IF subsystem IC Q1050
(TA31136FN). Demodulated signal from the SUB-RX FM
IF subsystem IC Q1050 (TA31136FN) is passes through
the low-pass filter Q1046 (2SC4154E) to the DSC Decod-
er IC Q1048 (NJM2211M) which the receiving DCS code
is decoded. The decoded DCS signal delivered to the 16-
bit MPU IC Q3004 (M30626FHPGP).
The SUB-RX 1st Local signal maintains stability from the
PLL synthesizer by using a 29.950 MHz reference signal
from crystal X1001. PLL synthesizer IC Q1034
(TB31202FNG) consists of a prescaler, reference counter,