Codan Radio Communications VT-3-150-SN User Manual
9-6
9.3
Audio Specifications
Audio Input:
-30 to 0 dBm into a 600
Ω
balanced load.
Audio Response:
Flat audio; +1/-3 dB: 300 Hz - 3 kHz
Audio Distortion:
Less than 3% -40˚C to +60˚C at 30% modulation,
Less than 5% -40˚C to +60˚C at 90% modulation
Less than 5% -40˚C to +60˚C at 90% modulation
9.4
Audio Circuits
All of the audio signal conditioning (e.g. limiting, filtering) is performed by the MT-3 AM Audio
Processor. The transmitter board routes the audio lines from the backplane connector to the
audio processor. The audio lines routed to the audio processor are: a 600 ohm balanced input
(pins B18 and Z18), and a MIC AUDIO from the MT-3 FRONT PANEL BOARD. It is here
that the MIC audio is processed in the same manner as the 600 ohm balanced audio. The audio
processor's balanced input pins are isolated from pins B18 and Z18 by a transformer (T1). Two
audio outputs from the MT-3 AM Audio Processor are routed to the VT-3A130 Amplifier.
Processor. The transmitter board routes the audio lines from the backplane connector to the
audio processor. The audio lines routed to the audio processor are: a 600 ohm balanced input
(pins B18 and Z18), and a MIC AUDIO from the MT-3 FRONT PANEL BOARD. It is here
that the MIC audio is processed in the same manner as the 600 ohm balanced audio. The audio
processor's balanced input pins are isolated from pins B18 and Z18 by a transformer (T1). Two
audio outputs from the MT-3 AM Audio Processor are routed to the VT-3A130 Amplifier.
The MT-3 AM Audio Processor is a versatile circuitboard that can provide several types of audio
processing. The module also has an on-board programmable push-to-talk (PTT) time-out-timer
(TOT) on an attached circuitboard. A continuous +9.5 Vdc supply and a continuous +13.8 Vdc
supply together with a switched +8.0 Vdc supply are required to power the module. Refer to
section 9.11 "MT-3 AM Audio Processor Component Layout" and to section 9.12 "MT-3 AM
Audio Processor Schematic Diagram" for component location and designation references.
processing. The module also has an on-board programmable push-to-talk (PTT) time-out-timer
(TOT) on an attached circuitboard. A continuous +9.5 Vdc supply and a continuous +13.8 Vdc
supply together with a switched +8.0 Vdc supply are required to power the module. Refer to
section 9.11 "MT-3 AM Audio Processor Component Layout" and to section 9.12 "MT-3 AM
Audio Processor Schematic Diagram" for component location and designation references.
9.5
Power Requirements
The audio processor can be configured for continuous audio standby or for switched audio
standby by the Transmitter Main Board. If fast audio risetime is desired, the transmitter should
be operated in standby mode 3 or 4 as specified below. The current for the associated TOT is
approximately 4 mA when the transmitter is keyed.
standby by the Transmitter Main Board. If fast audio risetime is desired, the transmitter should
be operated in standby mode 3 or 4 as specified below. The current for the associated TOT is
approximately 4 mA when the transmitter is keyed.
9.6
Transmitter Standby Modes
The VT-3A130 Transmitter has four different standby modes that trade-off standby current
consumption for start-up speed. The standby modes are determined by three jumpers: jumper J6
which always turns on the '+9.5 Vdc Switched' supply, jumper J7 which selects the power source
for the MT-3 AM Audio Processor and jumper J18 which selects the enable line for the OST-
3A128 Synthesizer Module.
consumption for start-up speed. The standby modes are determined by three jumpers: jumper J6
which always turns on the '+9.5 Vdc Switched' supply, jumper J7 which selects the power source
for the MT-3 AM Audio Processor and jumper J18 which selects the enable line for the OST-
3A128 Synthesizer Module.