Standard Horizon MATRIX GX3000S, Service Manual

Page: 7 / 54

7
Circuit Description
Reception and transmission are switched by 16-bit MPU
IC
Q3004 ( M30626FHPGP ) on the CNTL Unit. The re-
ceiver uses double-conversion superheterodyne circuit-
ry, with a 30.4 MHz 1st IF and 450 kHz 2nd IF. The 1st
local is produced by a PLL synthesizer, yielding the 30.4
MHz 1st IF. The 2nd local uses a 29.950 MHz crystal oscil-
lator, yielding the 450 kHz 2nd IF. The 2nd mixer and other
circuits use a custom IC to convert and amplify the 2nd IF
and detect FM to obtain demodulated signals. During
transmit, the PLL synthesizer oscillates at the desired fre-
quency directly, for amplification to obtain RF power out-
put. During transmit, voice modulation is applied to this
synthesizer. Transceiver functions, such as TX/RX control,
PLL synthesizer settings, and channel programming, are
controlled using the MPU.
Receiver
Incoming RF signals from the antenna connector are de-
livered to the RF Unit, and pass through a low-pass filter
(LPF) consisting of coils L1009 & L1010 and capacitors
C1010, C1017, & C1038, and antenna switching diode
D1005
( XB15A308 ) for delivery to the receiver front end.
Signals within the frequency range of the transceiver are
then passed through a bandpass filter consisting of coils
L1001 & L1002 and capacitors C1005, C1007, C1024, C1030,
& C1044, before RF amplification by
Q1018 ( 3SK294 ).
The amplified RF is then passed through a bandpass filter
again consisting of coils L1003, L1004, & L1005 and ca-
pacitors C1126, C1129, C1134, C1143, C1151, C1158, &
C1165, the pure in-band input signal is delivered to the
main 1st mixer which is composed of balun transformers
(T1001, T1002, and T1003) and quadrate FETs
Q1032 ,
Q1033 , Q1036 , and Q1037 (all 2SK520-K41 ).
Buffered output from the MAIN VCO is amplified by
Q1021
(
2SC5006
) and
Q1016
( 2SC3356-R25 ) and low-pass
filtered by coils L1034 and L1036 and capacitors C1179,
C1180, C1182, C1183 and C1187, to provide a pure 1st lo-
cal signal between 125.65 and 131.625 MHz for delivery
to the main 1st mixer.
The 30.4 MHz 1st mixer product is amplified by Q1042
( 2SC4400-3 ), then passes through monolithic crystal fil-
ters XF1003 and XF1004 (±6.5 kHz BW), and is amplified
by
Q1047 and Q1051 (both 2SC4400-3 ).
After that, it delivered to the input of the FM IF subsystem
IC
Q1049 (
TA31136FN
). This IC contains the 2nd mixer,
2nd local oscillator, limiter amplifier, FM detector, noise
amplifier, and squelch gates.
The 2nd local in the FM IF subsystem IC is produced from
crystal
X1001 (29.950 MHz), and the 1st IF is converted to
450 kHz by the 2nd mixer and stripped of unwanted com-
ponents by ceramic filter
CF1001 .
After passing through a limiter amplifier, the signal is
demodulated by the FM detector. Demodulated receive
audio from the FM IF subsystem IC is delivered to the AF
Unit, then amplified by
Q2009 and Q2010 (both
2SC4154E ). The amplified signal is passed through the
AF selector switch Q2012 ( CD4066BPW ) to the amplifier
Q2018 ( LM2902PW ). The amplified signal is passed
through the AF mute switch Q2012 ( CD4066BPW ) and
the electronic volume control IC Q2017 ( M62421FP ). The
adjusted audio signal is passed through the AF mute
switch
Q2016 ( RT1N441U ) to the AF power amplifier
Q2019 ( LA4425A ).
The amplified audio signal is delivered to the 8 Ohms in-
ternal loudspeaker and external Speaker terminal in the
accessory cable.
PLL Synthesizer
The 1st Local signal maintains stability from the PLL syn-
thesizer by using a 29.950 MHz reference signal from crys-
tal
X1001 . PLL synthesizer IC Q1034 ( TB31202FNG ) con-
sists of a prescaler, reference counter, swallow counter,
programmable counter, a serial data input port to set these
counters based on the external data, a phase comparator,
and a charge pump.
The PLL synthesizer IC divides the 29.950 MHz reference
signal by 2396 using the reference counter (12.5 kHz com-
parison frequency). The reference oscillator feeds to the
PLL synthesizer IC
Q1034 (
TB31202FNG
) for the 2nd lo-
cal signal.
The VCO output is divided by the prescaler, swallow
counter and programmable counter. These two signals are
compared by the phase comparator, and applied to the
charge pump.
A voltage proportional to their phase difference is deliv-
ered to the low-pass filter circuit, then fed back to the VCO
as a voltage with phase error, controlling and stabilizing
the oscillating frequency. This synthesizer also operates
as a modulator during transmit.
The MAIN VCO is consisted of Q1023 (
2SK520-K41
) and
varactor diodes D1008 , D1009 , D1010 , and D1011 (all
HVC306B
), which oscillates at 30.4 MHz below from the
receiving frequency. The MAIN VCO output passes
through buffer amplifier
Q1021 ( 2SC5006 ) to obtain sta-
ble output, then applied to the main 1st mixer. The DC
supply for the MAIN VCO is regulated by
Q1013
( 2SC4154E ).
The TX & SUB VCO is consisted of Q1031 ( 2SK520-K41 )
and varactor diodes D1014 , D1015 , D1016 , and D1017 (all
1SV286 ), which oscillates at 134.225 MHz for the CH70
receiving and the fundamental transmit frequency dur-
ing a transmit, with direct frequency-modulation using