Table of Contents
Advertisement
C2.8
T881 Circuit Operation
2.5
Audio Processor
(Refer to the audio processor circuit diagram (sheet 2) in Section 6.2.)
Carrier
Opto-coupler
+
Opto-Key
_
Constant Current Sink
Tx Key
PTT
Microphone
Pre-amp.
Microphone
Input
Line Input
Audio 1
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
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.
10/07/00
Link
3
4
Output
B
Inhibit
5
6
mic.
C
PL205
line
Multiplexer
Audio 2
Figure 2.5 T881 Audio Processor Block Diagram
for linking details.
Tx Enable
4
6
8
Compressor
PL215
Link
6
5
N
4
3
M
2
1
L
PL210
Pre-
emphasis
3
1
PL220
M880-00
Link
3
H
5
Limiter
I
7
J
Set Deviation
Digital Pot. (EPOT)
Σ
CTCSS
Link
4
E
Low Pass
2
Filter
D
Ref. Mod. Adjust
Digital Pot. (EPOT)
Integrator
Buffer
Output
Ref.
To VCO
Mod.
Copyright TEL
Advertisement
Chapters
Table of Contents
