Instruction Manual
DE
DANIELS
ELECTRONICS
MT-3 AM Transmitter Main Board Instruction Manual 2-7
2.3.3 Audio Circuitry
The MT-3 AM Tx Audio Processor refer to section 5.4.2 "MT-3 AM Audio Processor Schematic
Diagram" has two audio inputs (Microphone input and Balanced input) which can be used to
modulate the transmitter. The input signals are combined by R2 and R17 at a compandor U1.
U1b controls the input level and makes gain inversely proportional to the input level (say a 20 dB
drop in input level will produced a 20 dB increase in gain). The output will remain fixed at a
constant level without clipping and distortion. (Automatic Level Control) The input signals are
adjusted by the pots R1, R16. The variable gain cell in U1a is used as a voltage-controlled
amplifier so that if the power supply (13.8Vdc) has changed the output level will change in order
to keep the modulation of the RF output signal at the same level. The gain control can be adjust by
the pot R4. (Automatic Modulation Control) The audio signal then amplifies and filters at U2.
The output signal is adjusted by the pot R9.