Theory of Operation
14
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
Factory Configuration
The FM Audio Processor is factory configured as follows:
Parameter
Specification
Maximum Deviation
±5.0 kHz
Microphone Input
• 1 kHz signal at -10 dBm gives ±60% rated system deviation
• 1 kHz signal compression set at ±84% rated system deviation
Audio Balanced Input
• 1 kHz tone at -8 dBm gives pre-emphasis response ±60% rated
system deviation
• 1 kHz signal compression set at ±84% rated system deviation
Subtone Input 1
100 Hz tone at -18 dBm gives ±500 Hz
All Other Audio Inputs
Disabled
Interconnection Pin Layout Diagram
PCB
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
P1
P2
P4
P3
Balanced Input
END VIEW
Mic Input
Subtone Inp ut 1
+8V
+9.5V
Low Frequency
Direct Mod Output
Voice
And Subtone
Output
-8
dBm
-10
dBm
-18
dBm
Surface Mount Side
0
dBm
B0312
FIGURE 2
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.
