ABB ETL600 - Absolute Psophometrically Weighted Level L 0 P [Dbm0 P]; Conversion between Power and Voltage Levels

ETL600 1KHW001489-EN ABB Switzerland Ltd
Absolute mean or RMS level:
[]
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎭
⎬
⎫
⎩
⎨
⎧
∗=
∑
−
→∞
)(
1
limlog20
2
2
2
nX
n
dBmL
n
n
n
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎭
⎬
⎫
⎩
⎨
⎧
∗=
∑
−
∞→
)(
1
limlog10
2
2
2
nX
n
n
n
n
.
(13)
Absolute peak level:
[
]
{
}
(
)
∞<<−∞∗= nnXpeakdBmL ,)(maxlog20
{
}
(
)
∞<<∞−= nnX ,)(maxlog*10
2
.
(14)
Absolute peak envelope level:
[
]
{
}
(
)
∞<<∞−∗+−= nnXPEdBmL ,)(maxlog203
{
}
(
)
∞<<∞−+−= nnX ,)(maxlog*103
2
.
(15)
As the signal samples X(n) are dimensionless values, the levels given
above are neither voltage nor power levels. But in analogy to the levels
defined for analog signals, we use the terms “voltage level” or “power
level” according to the above formulas also for digital signals.
5.2.5. Absolute psophometrically weighted level L
0p
[dBm0p]
This is basically the same as L
0
, but the index "p" indicates a
psophometrically-weighted level, which is generally defined according
to ITU-T. This weighting is only used in connection with the
specification of noise levels on speech channels. The equivalent noise
bandwidth of the psophometrically-weighted filter is 1.74 kHz.
5.2.6. Conversion between power and voltage levels
For digital signals, no conversion is necessary, because power and
voltage levels are not distinguished.
For analog signals, the following formula applies:
[][ ]
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∗
∗+=
2
0
)775(
1
log10
mV
RmW
dBmLdBuL
u
[]
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∗+=
Ohm
R
dBmL
600
log10
0
.
(16)
where R
0
is the impedance of the measuring point.
Thus for an impedance of 600 Ohms, the voltage level L
u
is equal to
the power level L.
Configuration and Set-up November 2005 5-5