M850-00
2.1
Introduction
Mixer
Front
End
Synthesised
Local
Oscillator
12.8MHz
Master
Oscillator
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.
Copyright TEL
Mixer
45MHz
455kHz
IF
IF
Second
Local
Oscillator
Figure 2.1 T855 High Level Block Diagram
T855 Circuit Operation
Noise
Mute
Limiter
Audio
Processor
FM
Detector
Carrier
Mute
RSSI
B2.3
Speaker
}
600Ω
Line
31/09/98