DE
DANIELS
ELECTRONICS
MT-3 AM Transmitter Main Board Instruction Manual
3-5
To remove the Enhanced Synthesizer or Crystal Controlled Oscillator module, simply remove the
center screw from the module lid and pull the module out. The module should be pulled straight
out so that the four alignment pins do not bend or damage the circuitboard.
3 . 8
MT-3 AM Audio Processor Alignment
3 . 8 . 1
General
Verify the standard factory settings for the MT-3 AM Audio Processor as given in section 3.5.2
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 5.4.2 and the
component layout is shown in section 5.4.1.
3 . 8 . 2
MT-3 AM Audio Processor Adjustment
**note: clockwise rotation of controls increase 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 R1 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.
10)
Apply a 1 kHz, -8 dBm input signal, the modulation should be 90%, observe that the
distortion of the transmitted signal is within 5.0%.
