Tait T850 II Series, Service Manual

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C2.8 T856/857 Circuit Operation
M850-00
31/09/98 Copyright TEL
2.5 Audio Processor
(Refer to the audio processor circuit diagram (sheet 2) in Section 6.2 or 6.3.)
Figure 2.6 T856/857 Audio Processor Block Diagram
2.5.1 General
The audio processor comprises several link selectable circuit blocks which may be con-
figured in a variety of combinations to suit individual requirements. The pre-emphasis
network and compressor may be linked individually or cascaded between either or both
audio inputs and the limiter.
Refer to Section 3.5.1 for linking details.
2.5.2 Audio Inputs
Two audio inputs are available: one from a 600 ohm balanced (or unbalanced) line, and
the other from a local microphone. The microphone signal is passed first to a pre-ampli-
fier (Q210) and ultimately to a multiplexer (IC240), but in between may pass through
the compressor (depending on the linking details). The line transformer is also con-
nected to the multiplexer and is disabled by the microphone PTT switch.
A third input for external CTCSS tones is also provided.
Pre-
emphasis
3 4
6
B
C
5
6
4
3 4
2
5
3
3
5
7
1 2
8
N
H
M
I
E
L
J
D
4
6
1
mic.
line
Multiplexer
Inputs
Output
Output
Inhibit
Audio 1 Audio 2
Compressor
Link
Link
Link
Tx Enable
Σ
Carrier
Opto-Key
Tx Key
PTT
Microphone
Input
Line Input
Microphone
Pre-amp.
Opto-coupler
Link
PL205
PL215
PL220
PL210
Limiter
Set Deviation
CTCSS
Low Pass
Filter
Ref. Mod. Adjust
Integrator
Digital Pot.
Digital Pot.
Buffer
Output
To VCO
Ref.
Mod.
Constant Current Sink
+
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