Appendix A
Page 195
Appendix A INTERPRETATION OF LEVEL UNITS
This appendix discusses the relation between the simulator setting and the real noise it
represents.
In all cases the objective is to choose a setting that corresponds to the reading of a level
meter connected to the equipment. Since we know that the noise SOURCE is unchanged,
the reading will only change according to the bandwidth and the impedance of the meter
(designated the Load Impedance).
In Impairment modules the units used in setting levels are designed to give a compromise
between commonly used units and those that are unambiguous.
There are three forms of Units that are used.
1)
µ
V/
√
Hz – Is independent of the Load Impedance and the bandwidth of the measuring
device. It therefore requires the most manipulation to be translated into a meter read-
ing.
2)
dBm/Hz – Is independent of the bandwidth of the meter but not of the impedance.
Therefore, when using a setting of X dBm/Hz the Load Impedance must be previ-
ously defined.
3)
dBm – Is related to both Load Impedance and bandwidth. When using a setting of
X dBm the Load Impedance and the bandwidth must both have been previously
defined.
Following is a set of examples on how to convert a unit to dBm, the most common readout
of level meters.
1)
µ
V/
√
Hz to dBm
For this example we will assume that the load impedance is 135
Ω
and the bandwidth is
3 kHz.
Assume that the setting is 10
µ
V/
√
Hz :
V * V
= (
µ
V/
√
Hz ) * (
µ
V/
√
Hz) * Bandwidth
= (10E–6) * (10E–6) * 3000
= 3.00E–7
Summary of Contents for DLS 400A
Page 1: ...Revision 0 21 September 1999 TestW rks Operating Manual DLS 400A H N HN Wireline Simulator ...
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