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14
Theory of Operation
For the interconnections and functions of the FM Audio Processor external connections, see
Figure 2. Connectors P1, P2, P3, and P4 are four-pin audio processor headers soldered directly to
the transmitter mainboard. For troubleshooting isolation, the audio processor could be unsoldered
from the mainboard and analyzed. Power and I/O connections, as well as their expected levels, are
shown in this diagram.
P3
4
2
3
1
Voice
And Subto ne
Output
B0312
Factory Configuration
The FM Audio Processor is factory configured as follows:
Parameter
Maximum Deviation
Microphone Input
Audio Balanced Input
Subtone Input 1
All Other Audio Inputs
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
P4
P2
PCB
4
2
4
2
3
1
3
1
+9.5V
+8V
Low Frequen cy
Direct Mod Output
Interconnection Pin Layout Diagram
Specification
±5.0 kHz
• 1 kHz signal at -10 dBm gives ±60% rated system deviation
• 1 kHz signal compression set at ±84% rated system deviation
• 1 kHz tone at -8 dBm gives pre-emphasis response ±60% rated
system deviation
• 1 kHz signal compression set at ±84% rated system deviation
100 Hz tone at -18 dBm gives ±500 Hz
Disabled
Surface Mou nt Side
Mic Input
-10
dBm
Subtone Inp ut 1
-18
dBm
P1
4
2
END VIEW
3
1
Balanced Input
0
-8
dBm
dBm
FIGURE 2
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