Analog Mode Of Operation; Figure 3-2. Receiver Block Diagram - Motorola ASTRO XTS 5000 Basic Service Manual

3-2
3.2

Analog Mode of Operation

This section provides an overview of the analog mode receive and transmit theory of operation.
3.2.1 Receiving
When the radio is receiving
Transceiver board, passing through the antenna switch and the receiver front end. The signal is then
filtered, amplified, and mixed with the first local-oscillator signal, generated by the voltage-controlled
oscillator (VCO).
RF Input
Harmonic
Filter
XTAL
Filter
The resulting intermediate frequency (IF) signal is fed to the IF circuitry, where it is again filtered and
passed to the Abacus III digital back-end IC. In the digital back-end IC, the IF signal is mixed with the
second local oscillator to create the second IF at 2.25 MHz. In the back-end IC, a bandpass, sigma-
delta, analog-to-digital converter then decodes the second IF signal, and outputs, on the radio's
serial synchronous interface (SSI) bus, digital audio to the VOCON board.
On the VOCON board, the dual-core processor's digital-signal processor (DSP) digitally filters the
PCM audio. The DSP decodes the information in the signal and identifies the appropriate destination
for it.
• For a voice signal, the DSP will route the digital voice data to the CODEC inside the audio and
power supply support IC, for conversion to an analog signal. The CODEC will then present the
signal to the receive audio pre-amplifier, then to the audio power amplifier, which drives the
speaker.
• For signaling information, the DSP will decode the message and pass it internally to the
microcontrol unit of the dual-core processor.
July 16, 2004
(See Figure 3-2), the signal comes from the antenna connector to the
RX Front End
Tuneable
Preselector
Antenna
Filter
Switch
ABACUS III - RX Back End
LO

Figure 3-2. Receiver Block Diagram

Basic Theory of Operation: Analog Mode of Operation
Tuneable
1st LO
Preselector
Filter
LNA
ADC
CKO
1st
Mixer
3
RX_SSI_ DATA
to VOCON Board
MAEPF-27278-A
6881094C28-D