ABB ETL600, Instruction Manual

Page: 150 / 382

ABB Switzerland Ltd
1KHW001489-EN ETL600
Example:
The power level at the 75 Ohm RF output of a PLC equipment is 40 dBm. What is the
voltage level L
U
?
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
∗ + =
Ohm
Ohm
dBm L
u
600
75
log 10 40
dBu 31
=
.
5.2.7. System power level L0 [dBm0]
The system power level L
0
is used in order to define the level of a
signal in a system regardless of the measuring point.
The dBm0 value defines by how many dB a signal is greater or less
than a reference signal, which thus is defined to have an system
power level of 0 dBm0. In the ETL, the reference signal is the average
nominal speech level at the two-wire output.
The system power level is a property of the signal and doesn’t depend
on the measuring point. As such, it is used to define signal levels
without reference to a specific measuring point.
Each signal has specific average (dBm0), peak (dBm0 peak) and peak
envelope (dBm0 PE) system power levels.
5.2.8. Relative power level Lrel [dBr]
The relative power level Lrel defines the signal levels at various points
of a system without reference to the applied signals.
The dBr value is the difference between absolute power level L and
system power level L
0
:
[ ] [ ] [ ]
0
0
dBm L dBm L dBr L
rel
− =
.
(17)
The relative power level is a property of the measuring point and
doesn’t depend on the signal.
5.2.9. Level measurements
Test sockets allow the measurement of some internal signal levels. In
case of decoupled test sockets, this is possible without influence on
the signals being measured,. However, the voltage level at the test
socket depends on the input impedance of the measuring set being
used. Therefore, this impedance must be specified for each test socket
of the equipment. For the ETL600, input impedances
≥
5 kOhms (also
referred to as “infinite”) or 50 Ohms are specified.
The decoupling circuitry of the test socket normally amplifies or
attenuates the level to be measured by an amount of A
ts
[dB] in order
to bring it in a range suitable for measurement. The power level L of
the internal signal to be measured can then be calculated from the
voltage level L
u|ts
at the test socket via the relationship
5-6 November 2005 Configuration and Set-up