User's Guide

Audio Processor Board Instruction Manual 1-1
1 F M A U D I O PROC E SSOR
1.1 Introduction
The MT-3 FM Audio Processor is a versatile circuit board that can provide several types of audio
processing for voice or data transmission.
The following terms are defined:
Table 1 Bandwidth Definition
Term Channel Spacing Rated System Deviation
Wideband 25 kHz or 30 kHz ± 5.00 kHz
Narrowband 12.5 kHz or 15 kHz ± 2.50 kHz
LTR™ is a trademark of E.F. Johnson Co.
Features include:
• Automatic level control using a compression amplifier with a 25 dB dynamic range
• Limiter and Splatter filter that removes noise and harmonics
• Selectable pre-emphasis or flat audio response
• Temperature compensated audio output
• Ability to transmit data and voice switched by a single control line.
• Backwards compatible with Daniels Electronics MT-2 series transmitters.
• Direct modulation input for LTR™, DCS, paging and other digital modulations that
require very low frequency modulation to the synthesizer or crystal oscillator module.
• Separate voice and direct modulation outputs, each individually configurable.
• Multiple jumpers that can be configured to allow maximum flexibility in routing signals
from inputs to outputs, and disabling selected circuits to reduce operating current.
• Dual microphone and balanced audio compression circuits.
• On-board multi-configurable temperature compensation to correct for changes in
transmitter deviation over temperature caused by changing characteristics of synthesizers
and oscillators.
• A single chip 10th Order Linear Phase Lowpass splatter filter for increased cutoff
attenuation responses needed in today ’ s narrow band environment.
• The ability to switch between narrow and wideband through a single control line which
can be externally controlled. This can be useful when configured as a multi-channel
transmitter which uses mixed wide and narrowband frequencies.
• The ability to easily reconfigure fixed operations from narrow to wideband through
simple jumper settings