Motorola SSETM 5000 - Manual (Page 25)

6881094C12-A November 11, 2004
Theory of Operation: Mode of Operation 2-3
2.2.2 Transmitting
When the radio is transmitting, microphone audio is passed through gain stages to the CODEC,
where the signal is digitized (see
Figure 2-3 ). The CODEC passes digital data to the DSP, where pre-
emphasis and low-pass (splatter) filtering are done. The DSP passes this signal to a digital/analog
converter (DAC), where it is reconverted into an analog signal and scaled for application to the
voltage-controlled oscillator as a modulation signal.
Figure 2-3. Transceiver (UHF Range) Block Diagram (Power and Control Omitted)
Transmitted signaling information is applied to the DSP from the microcontrol unit, where it is coded,
and passed to the DAC, which handles it the same as a voice signal. The DAC output connects to
the synthesizer modulation input. A modulated carrier is provided to the transmitter power amplifier,
which transmits the signal under dynamic power control.
Reference
Oscillator
FracN
MOD
IN
Loop
Filter
LPF
FL200
Y200
DAC
U203
VCO 1
VCOBIC
VCO 2
Crystal
Filter
Mixer
2ND
LO
Sample
Clk
RX_SSI to
VOCON Board
TX_SSI from
VOCON Board
Preselector
Filter
PCIC
U104
Power
Module
Q107
TX
Buffer
TX Driver
Amplifier
U102
D101
Directional
Coupler
U101
Dual
Antenna
Switch
Preselector
Filter
RX LNA
Serial EE
PROM
U4
ABACUS III U500
MAEPF-27530-A
3
3
Note:
This UHF range has 2 VCOs
(1 TX, 1 RX) To
Remote
Port
To
Antenna
Harmonic
Filter