M850-00
T855 Circuit Operation
B2.3
Copyright TEL 31/09/98
2.1 Introduction
Figure 2.1 T855 High Level Block Diagram
The T855 receiver consists of a number of distinct stages:
• front end
•mixer
• synthesised local oscillator
•IF
• audio processor
• mute (squelch)
• regulator circuits
• received signal strength indicator (RSSI).
These stages are clearly identifiable in Figure 2.1. Refer to the circuit diagrams in Sec-
tion 6 for further detail.
45MHz
IF
455kHz
IF
Carrier
Mute
RSSI
Noise
Mute
Front
End
12.8MHz
Master
Oscillator
Audio
Processor
Mixer Mixer Limiter
FM
Detector
Synthesised
Local
Oscillator
Second
Local
Oscillator
Speaker
}
600Ω
Line
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