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© MiMOMax 2013 Four Wire Audio
Interface Manual
4
AUDIO INTERFACES
4.1
O
VERVIEW
The Four Wire Audio and E&M Signalling Interfaces are intended to provide point-to-point
audio paths as would be required for back-haul linking of PMR base stations and trunking
sites. Additionally the Four Wire Audio interfaces are able to be used for signalling (modems)
as used by protection relays for power system protection and SCADA applications. The Four
Wire Audio interface is able to act as a replacement for copper lines normally used for 4 wire
audio and E&M signals (Note: Modems up to 4800 bps only are supported).
There are six audio channels incorporated into the Four Wire Audio interface where each
audio channel is coded into the G726 32kbps ADPCM format. Dynamic (E&M controlled) and
static (always up, E&M independent) channel operation is supported.
CODEC
PROCESSING
T
ra
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s
fo
rm
e
r
(6
0
0
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m
)
Audio Data
Four Wire Audio Unit
T
ra
n
s
fo
rm
e
r
(6
0
0
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)
8
6
3
5
1
2
4
7
E&M
LOGIC
DC Block
M-Lead
E-Lead
Audio Output
Audio Input
Shield
Four Wire Audio
Port
Circuit Overview
Note: An E-Lead Signal is required for audio to pass unless a ‘Static’ or ‘Fixed’ channel
configuration is selected.
4.2
A
UDIO
Each audio port provides a balanced 600ohm transformer-isolated Four Wire Audio interface
and an E&M signalling interface.
There is nominally 0.6dB ±0.3dB of gain in the audio path at 1kHz (This is NON configurable).
The audio transport is achieved using a G726 32 kbps ADPCM vo-coder. This provides tone
transparent high quality audio.
The input audio levels and frequency ranges are as follows.
-20 to +9 dBm (320
– 3500 Hz)
-20 to -10 dBm (65 - 320 Hz)
Voice Frequency modems up to 4800 bps are supported.
