Codan Radio Communications VT-3-150-SN User Manual
Transmitter Main Board Instruction Manual
2-11
2.3.4.5
Audio Processor Microphone Input
The microphone input has an automatically gain controlled (AGC) preamplifier whose input level is
controlled by R2. The microphone input level control (R2) can accommodate a -25 dBm to 0 dBm
input signal. The compression level for the microphone input is adjusted by R8. The microphone
input is limited and filtered and is output at the standard modulation output port.
controlled by R2. The microphone input level control (R2) can accommodate a -25 dBm to 0 dBm
input signal. The compression level for the microphone input is adjusted by R8. The microphone
input is limited and filtered and is output at the standard modulation output port.
2.3.4.6
Audio Processor Balanced Input
The 600 ohm balanced input also has an AGC preamplifier, input level control (R31), and
compression level control (R38). The balanced input level control can accommodate a -25 dBm to
0 dBm input. The balanced input can have a standard 6 dB/octave pre-emphasis response by
enabling jumper JU9 or a flat-audio response by enabling jumper JU10. Like the microphone
input, the balance input is limited and filtered and is output at the standard modulation output port.
compression level control (R38). The balanced input level control can accommodate a -25 dBm to
0 dBm input. The balanced input can have a standard 6 dB/octave pre-emphasis response by
enabling jumper JU9 or a flat-audio response by enabling jumper JU10. Like the microphone
input, the balance input is limited and filtered and is output at the standard modulation output port.
2.3.4.7
Audio Processor Auxiliary Input
The auxiliary input is a special input and does not have an AGC preamplifier or an input level
control. This input can be configured for a pre-emphasis response (enable JU14) or a flat-audio
response (enable JU15). The compression level for this input is set by R48. The auxiliary output
is normally summed with the voice signals by op-amp U4a, limited, then filtered and output at the
standard modulation output port. When jumper JU6 is disabled and jumper JU7 is enabled, the
auxiliary input can be used to directly modulate the transmitter. Care should be taken when directly
modulating the transmitter with the auxiliary input because the MT-3 transmitters use direct FM
modulation and there is no filtering or limiting action provided by the auxiliary input. The input
level to the auxiliary input should be -18 dBm and can be driven by one of three inputs:
control. This input can be configured for a pre-emphasis response (enable JU14) or a flat-audio
response (enable JU15). The compression level for this input is set by R48. The auxiliary output
is normally summed with the voice signals by op-amp U4a, limited, then filtered and output at the
standard modulation output port. When jumper JU6 is disabled and jumper JU7 is enabled, the
auxiliary input can be used to directly modulate the transmitter. Care should be taken when directly
modulating the transmitter with the auxiliary input because the MT-3 transmitters use direct FM
modulation and there is no filtering or limiting action provided by the auxiliary input. The input
level to the auxiliary input should be -18 dBm and can be driven by one of three inputs:
• the balanced input – JU11 enabled
• the tone/digital input – JU12 enabled
• the direct modulation input – JU13 enabled
• the tone/digital input – JU12 enabled
• the direct modulation input – JU13 enabled
When the 600 ohm balanced input is connected to the auxiliary input, the balanced input level
control can be used to adjust the level for the auxiliary input. When either the tone/digital input or
the direct modulation input are used, the input level is not adjustable.
control can be used to adjust the level for the auxiliary input. When either the tone/digital input or
the direct modulation input are used, the input level is not adjustable.
2.3.4.8
Audio Processor Subtone Inputs
There are two subtone inputs available on the audio processor. Both subtone inputs can be
individually configured to be output from the standard Modulation Output port or to be output from
the Low Frequency / Direct Modulation Output. In standard configuration, Subtone 1 is summed
individually configured to be output from the standard Modulation Output port or to be output from
the Low Frequency / Direct Modulation Output. In standard configuration, Subtone 1 is summed