Daniels VT-3/140-SWA2, Instruction Manual

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3-10 Transmitter Main Board Instruction Manual
3.10 MT-3 Audio Processor Alignment (Version 1.8)
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3.10.1General
Verify the standard factory settings for the MT-3 Audio Processor as given in section 3.9.1 before
beginning the standard deviation 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 5.5.2 and the component layout is
shown in section 5.5.1.
3.10.2MT-3 Audio Processor Standard Deviation Adjustment
Note: clockwise rotation of controls increases signal levels.
1 Connect the transmitter to the radio communications test set and monitor FM
deviation, distortion, and audio frequency. Before adjusting the audio deviation,
confirm that the transmitter RF output frequency is correct.
2 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.
3 Increase the balance level control (R31) so that the deviation increases until
compression is observed.
4 Adjust the compression control pot (R38) for compression at ±60% maximum
deviation.
5 Set the audio frequency to 2.4 kHz, then adjust the deviation control (R29) for
maximum deviation.
6 Reset the modulating frequency to 1 kHz and re-adjust R38 for ±60% maximum
deviation.
7 Repeat steps 4 and 6 until both conditions are met.
8 Vary the audio signal from 1 kHz to 3 kHz and measure the positive deviation and
then the negative deviation. Adjust the symmetry control (R14) until the ± deviation is
symmetrical. The variation between ± deviation levels should not exceed 300 Hz over
the 1 kHz to 3 kHz range.
9 Repeat steps 4 and 6 and re-adjust if necessary.