Daniels VT-3/140-SWA2, Instruction Manual

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Audio Processor Board Instruction Manual 9-7
The actual current and start-up time may depend on the frequncy controlled source (crystal or
synthesizer) and amplifier module. The current and start-up times given below are representative
values intended only as a guideline.
MODE 1: Jumper J6 out
- the audio processor is switched by a PTT signal
- the synthesizer is switched by a PTT signal
- standby current typically 13 mA
- start-up time typically 40 ms
MODE 2: Jumper J6 in, jumper J7 in the 'y' position, jumper J18 in the 'x' position
- the audio processor is switched by a PTT signal
- the synthesizer is enabled all of the time
- standby current not used in this mode
- start-up time not used in this mode
MODE 3: Jumper J6 in, jumper J7 in the 'x' position, jumper J18 in the 'y' position
- the audio processor is enabled all of the time
- the synthesizer is switched by a PTT signal
- standby current typically 19 mA
- start-up time typically 40 ms
MODE 4: Jumper J6 in, jumper J7 in the 'x' position, jumper J18 in the 'x' position
- the audio processor is enabled all of the time
-the synthesizer is enabled all of the time
-standby current typically 163 mA
-start-up time typically 12 ms
9.7 Audio Circuitry
The MT-3 AM Tx Audio Processor refer to section 9.12 "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 R14.