TMC Radio SRP 9100, Service Manual

Page: 38 / 66

Page 4.2
3 ~ TECHNICAL DESCRIPTION
Harmonic
Filter
L582-L585
Antenna
Switch
D540,
D541,
D580
Bandpass
Filter
RF Amp
Q400
BandPass
Filter
Mixer
T400
IF Amp
Q401
4 Pole
45MHz IF
Filters
Z401A/B
IQ
Demodulator
U400
RX/TX
AF
Switch
U800A
ADC/DAC
Codec
U820
RX AF
Switch
U302C
AF Amp
U850
Speaker
Switch
Q860,
Q861
PWM AGC
Integrator
From
PLA
To TX PA From PLA
Tx Audio
In
From PLA/DSP
TX MOD To TX
VCO / Phase
Modulator
SPKR_ON
TUNE_1, 2 , 3 & 4
I Q
Noise Blanker
E0 Only
To External
Accessory
RX/Disc
AF Switch
U302B
Diff. Amp
U402
TX/RX
Switch
D610/D611
VCO Buffer
Q604/Q605
Synthesiser
Buffer
Q607
RX VCO
Q600
RX VCO
Switch
Q601
to U701
SYNTH
VCO
Control Volts
RX_PSU
90 MHz
VCO
Q402
ACK_LO2
AUX_CP
to U701
from U701
CPP
From PLA
TX_MODE
AGC
Figure 4-1 VHF/UHF Receiver Block Diagram
4.1.4
Receiver Audio Processing
The base band audio from the IQ Demodulator is applied to a differential amplifier that cancels out DC offsets
and converts the balanced demodulator I/Q output signals to unbalanced inputs for the CODEC U820.
All receiver audio processing and filtering functions are performed by the CODEC under the control of the DSP.
The receiver I and Q analogue baseband signals are converted to digital signals by the CODEC ADC before
being applied to a series of digital filters which provide the final stage of adjacent channel filtering, high pass
and low pass filtering, mute noise processing and volume control for narrow and wideband operation. The fully
processed signal is then converted to an analogue audio signal by the CODEC DAC and then applied to
conventional dual speaker amplifier U850-1.
Dual audio amplifier U850 provides an audio output level of up to 500mW watts into the 16 ohm speaker. The
carrier and signalling mute functions are performed by Q860/861 under DSP control. De-emphasis to the
audio is performed within the DSP.
In addition, Discriminator Audio is derived from the other CODEC output channel and then amplified by U802A
after which it is applied to one of the radio I/O connectors for option purposes. Discriminator Audio is a preset
level set by the FPP and is independent of squelch operation. Switch U302B can select either flat or de-
emphasised audio from the CODEC DAC U820-24. The selected audio is applied to the other half of the audio
amplifier U850-2 that drives the options connector audio after which it is routed to the portable’s options
connector.