Overview 2-1
Section 2
THEORY OF OPERATION
1.0 Overview
1.1 Purpose
This section defines the theory of operation (or the Circuit Description) for the radio. At the same
time, it provides a description of the circuit theory and analysis of the radio hardware design.
1.2 General Description
The radio comprises of one main PCB. This main PCB contains the RF and digital circuits. The VHF/
UHF compliant handheld transceivers consists of a receiver, a transmitter, a phase-locked loop
(PLL) frequency synthesizer, control circuits and power supply circuits.
2.0 Receiver System
The receiver is a double conversion super heterodyne with first IF frequency at 45.1MHz and
second IF frequency at 455kHz.
2.1 Front-End
The front-end consists of a low pass filter, pre-selector filter, RF Amplifier, and a post-selector filter.
The receive signal from the antenna is applied to TX LPF (L409, L410, C426, C427, C428, C429,
C430) and then routed to an RF amplifier (Q301) after passing transmit / receive switch (CR401,
CR301, CR302) and the pre-selector. The signal from the pre-selector is amplified around 13dB at
LPF
ANT-SW
VCO
PRESLECTOR
FILTER
Q301
LNA
POST SELECTOR
FILTER
1'ST MIX
Q302
MCF
45.1MHz
IF AMP
Q303
CR301,2
F.T.V.
IF,MIX
U201
CF1,2
N/S
SW
X-TAL
44.645MHz
DESCRIMI
NATOR
455C24
Recovered AUDIO
Inj FILTER
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