User's Guide

9-8
9.8 AM Audio Processor Factory Configuration
The MT-3 AM Transmitter Audio Processor is factory configured as follows:
• Microphone Input: 1kHz tone at -10 dBm gives 50% maximum
modulations.
• Audio Balanced Input: 1 kHz tone at -8 dBm gives 90% maximum
modulations.
• Automatic Modulation Control enabled
• Automatic Level Control enabled
The corresponding jumper settings are:
• Jumper JU1: 'x' position Automatic Modulation Control disabled
• Jumper JU2: not installed Modulation configuration
• Jumper JU3: 'y' position Automatic Level Control enabled
• Jumper JU4: not installed Time-out-time power supply (optional)
• Jumper JU5: 'y' position Voice application
• Jumper JU6: 'y' position Voice application
• Jumper JU7: not installed Modulation configuration
• Jumper JU8: 'y' position Automatic Level Control enabled
• Jumper JU9: installed Power AMC and Microphone enabled
9.9 AM Audio Processor Alignment
Verify the standard factory settings for the MT-3 AM Audio Processor as given in section 9.8
before beginning the standard modulation adjustment procedure. If the transmitter's channel
frequency changes, the audio processor should be realigned to optimize the transmitter's
performance. The schematic diagram for the audio processor is shown in section 9.12 and the
component layout is shown in section 9.11.
*Note: clockwise rotation of controls increases signal levels
1 Before adjusting the audio board, confirm that the transmitter frequency is correct.
2 Unscrew and slide out the case of the transmitter. Locate the Tx Audio Board.
3 Connect the transmitter RF Output to a Radio communications test set.
4 Connect the 600 ohm input to the incoming audio (pins B18, Z18). Set the audio
frequency to 1 kHz at the desired level of -8 dBm.
5 Turn the transmitter on.
6 Adjust the pot R16, in order to achieve about 0.700 Vrms at TP4.
7 Adjust the pot R14, in order to achieve about 0.200 Vrms at TP8.
8 Tune the Audio Adjust pot R35 on the Power Amplifier board to obtain 90% modulation.
9 Apply a 1 kHz, -20 dBm input signal and adjust the pot R16 in order to obtain 30%
modulation.