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12
Theory of Operation
fm a u d I o Pr oC eS So r
Introduction
The FM Audio Processor is a versatile circuit
board that can provide several types of audio
processing for voice or data transmission (see
Figure 1).
Bandwidth table
term
Channel Spacing
wide band (wB)
25 kHz or 30 kHz
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
•
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
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
•
A single chip 10
Pass Splatter Filter for increased cut-off
attenuation responses
•
Separate voice and direct modulation
outputs, each individually configurable
•
Direct modulation input for LTR®, DCS,
paging and other digital modulations that
require very low frequency modulation to the
rated
System deviation
synthesizer module
±5.00 kHz
•
Multiple audio inputs for various audio filter
or modulation configurations
NOTE: If dual mode CTCSS and LTR® / DCS
A continuous +9.5 VDC supply and a switched
+8.0 VDC supply are required to power the
module which is normally supplied by the
transmitter mainboard.
The FM Audio Processor's balanced input
pins are isolated by a transformer (T1) on the
transmitter mainboard. Two audio outputs
from the FM Audio Processor are routed to the
synthesizer module.
Order Linear Phase Low
th
is desired in the same transmitter, it may
be possible with dual port modulation
synthesizers. It is not feasible with single
port modulation synthesizers. These
synthesizers are characterized by the
lack of a modulation port in their VCO
circuit. Contact the Daniels factory for
further details.
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