Motorola GM140 Informazioni sul servizio - Pagina 11
Sfoglia online o scarica il pdf Informazioni sul servizio per Radio Motorola GM140. Motorola GM140 34. Gm series professional radio uhf (403-470mhz)
Anche per Motorola GM140: Manuale di servizio di base (46 pagine), Informazioni sul servizio (32 pagine), Informazioni sul servizio (32 pagine)
Stampa la pagina
1.0
Introduction
This Chapter provides a detailed theory of operation for the VHF circuits in the radio. For details of
the theory of operation and trouble shooting for the the associated Controller circuits refer to the
Controller Section of this manual.
2.0
VHF (136-174MHz) Receiver
2.1
Receiver Front-End
The receiver is able to cover the VHF range from 136 to 174 MHz. It consists of four major blocks:
front-end bandpass filters and pre-amplifier, first mixer, high-IF, low-IF and receiver back-end. Two
varactor-tuned bandpass filters perform antenna signal pre-selection. A cross over quad diode mixer
converts the signal to the first IF of 44.85 MHz. High-side first injection is used.
Antenna
Pin Diode
Antenna
Switch
RF Jack
Harmonic
Filter
Recovered Audio
RSSI
455kHz Filter
455kHz Filter
Varactor
RF Amp
Tuned Filter
Control Voltage
from PCIC
Demodulator
IF
(25kHz)
(12.5kHz)
Figure 2-1 VHF Receiver Block Diagram
THEORY OF OPERATION
Varactor
Tuned Filter
First LO
from FGU
Limiter
455kHz Filter
(25kHz)
455kHz Filter
(12.5kHz)
Chapter 2
1. Crystal
Mixer
1. IF Amp
Filter
2. Crystal
2. IF Amp
Filter
Second LO
Filter Bank Selection
from Synthesizer IC