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342-86400-445PS
Issue
4.0
October
2006
Page
84
Copyright
GE Multilin Inc. 2002
The Transmission Level Points (TLP) are typically set 5dB above the signal level
that is transmitted in. This is to reduce the quantization error for VF voice
frequencies. The signal can exceed the TLP by up to 3.17dBm for µ-law and
3.14dBm for A-law without distortion of the signal.
Since most phones transmit at or around -9dBm, the transmit-in TLP should be
set around -4dBm or greater (typically 0dBm).
The receive-out TLP for the 86445-3X 2W FXS unit is nominally set at -2dBm (if
line impedance is 600 ohms) but should be set for the best voice quality for the
phone set being used.
Tip
Ring
0 dBm0
point
TX
RX
FXS
TX
RX
0 dBm0
point
A
N
A
L
O
G
D
I
G
I
T
A
L
A
N
A
L
O
G
D
I
G
I
T
A
L
Tip
Ring
FXO
4W / 2W
HYBRID
4W / 2W
HYBRID
P
A
B
X
Tip
Ring
0 dBm0
point
TX
RX
FXS
TX
RX
0 dBm0
point
A
N
A
L
O
G
D
I
G
I
T
A
L
A
N
A
L
O
G
D
I
G
I
T
A
L
Tip
Ring
FXO
4W / 2W
HYBRID
4W / 2W
HYBRID
P
A
B
X
Figure 13:
VF Transmission Level Settings
NOTE 1: The term dB is a ratio of power where positive dB is gain and negative
dB is loss, whereas dBm is a measure of absolute power in decibels relative to
1mW where 0dBm is 1 mW.
NOTE 2: The term dBm0 is used to express the difference in power between a
signal at any point in a voice network and a reference Transmission Level Point
(TLP) chosen as zero reference level for that point in the network. The dBm0
value of a signal with an absolute power of -10dBm, at a TLP of -5dBm, would be
-5dBm0, 5dB below the reference level. That same signal with an absolute
power of -10dBm, at a TLP of -15dBm, would have a value of +5dBm0, 5dB
greater than the reference level. To calculate the dBm0 value use the following:
Absolute Power (dBm) – TLP = dBm0
Using this formula for the two examples above: -10 – (-5) = -5 dBm0
-10 – (-15) = +5 dBm0