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4-2 TRANSMITTER CIRCUITS
4-2-1 MICROPHONE AMPLIFIER CIRCUIT
(RC-26, MAIN AND DSP UNITS)
The microphone amplifier circuit amplifies microphone
audio signal to a level needed for the DSP circuit.
Audio signals from the [MIC] connector (J8701, pin 6) are
amplified at the AF amplifier (IC8280, pin 3), and then
applied to the gate modulator IC (MAIN unit; IC2001, pin
3) via the J2051, pin 1 as "FMOD" signal. The signal is
applied to the DSP unit after being passed through the AF
amplifier and low-pass filter IC (MAIN unit; IC1051, pins 3, 7)
as "DSPI1" signal.
4-2-2 DSP TRANSMITTER CIRCUIT (DSP UNIT)
The DSP (Digital Signal Processor) circuit enables PSN
(Phase Shift Network)/Low Power/Phase modulator,
transmitter monitor, side tone, and etc.
The microphone audio signals from the MAIN unit via the
"DSPI1" line are amplified at the differential amplifiers
(IC9651a/b), and are then applied to the A/D converter
section in the CODEC IC (IC9501). at the same time, the
converted signals are level-shifted 5 V to 3.3 V in the IC
(IC9501).
The level shifted signals are applied to the DSP IC (IC9301)
and modulated at the DSP IC to produce the 12 kHz
transmitter IF signal.
The modulated IF signal from the DSP IC is applied to the
D/A convertor section in the CODEC IC (IC9501) to convert
into the analog IF signal. Also the signal is level-shifted
3.3 V to 5 V at the level converter section in the IC (IC9501).
The level-shifted IF signal is passed through the active filter
(IC9701a), and then applied to the MAIN unit via J9901 (pin
17) as the "DSPO1" signal.
4-2-3 SPEECH COMPRESSOR CIRCUIT
(DSP UNIT)
The DSP (Digital Signal Processor) circuit enables PSN.
The speech compressor compresses the transmitter audio
input signals to increase the average output level (average
talk power).
• TRANSMIT CONSTRUCTION
MIC
Controller
AMP.
2nd mixer
FI201
D303
64.455 kHz
Crystal
BPF
Bandwidth:
2nd LO (64.00 MHz)
15 kHz
IC2001
IC1051
3
1 5
VCA
AMP.
LPF
1st mixer
Q702, Q703
RF
amp.
Q401
1st LO
(64 94 MHz)
When the speech compressor function is ON, the level-
shifted signal from the CODEC IC (IC9501) is applied to
the DSP IC (IC9301) and compressed at the DSP IC to
obtain an average audio level.
At the same time, the compressed signals are modulated
at the DSP IC and applied to the D/A converter section in
the CODEC IC (IC9501).
4-2-4 IF AMPLIFIER AND MIXER CIRCUITS
(MAIN UNIT)
The modulated 3rd IF signal from the DSP unit ("DSPO1"
signal: 12 kHz) passes through the transmit/receive switch
(IC1703, pins 1, 6), and then applied to the 3rd mixer circuit
(IC901, pin 3). The applied 3rd IF signal is mixed with the
3rd LO signal from the DDS circuit (PLL unit; IC5701) to
produce a 455 kHz 2nd IF signal.
The 2nd IF signal is output from IC901, pin 5 and passes
through the ceramic bandpass filter (FL402) to suppress
the unwanted signals via the D132. The filtered 2nd IF
signal is amplified at the 2nd IF amplifier (Q801), and then
applied to the 2nd mixer circuit after being passed through
the D305 and low-pass filter (L305, L306, C307, C308,
C310, C311, C315).
The 2nd IFsignal is mixed with 64 MHz 2nd LO signal,
coming from the PLL circuit, at the 2nd mixer circuit (D303)
to obtain 64.455 MHz 1st IF signal. The 1st IF signal is
passed through the bandpass filter (FI1201) to cut off the
unwanted signals. The signal is applied to the transmitter
mixer circuit (Q702, Q703) to obtain the desired signal via
the transmit/receive switch (D205) and attenuator (R712,
R715, R716).
The operating (transmitting) frequency is produced at the
1st IF mixer circuit (Q702, Q703) by mixing the 1st IF and
1st LO signals. The mixed signal is then applied to the RF
circuit.
7
DSP
1
6
7
UNIT
DSPI1
DSPO1
(12 kHz)
IC1001
0.5 1.9999 MHz
IC1
LPF
YGR
BPFs
2 30 MHz
4 - 3
3rd LO
(443 kHz)
455 kHz
Ceramic
BPF
FI402
PA UNIT
FILTER UNIT
AMPs
LPFs
Q6106, Q6401,
Q6402, Q6801,
Q6851
Q801
AMP.
Antenna
PWR
DET
D7271,
D7272
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