Fluke CableAnalyzer DSX-5000, Техническое справочное руководство, Страница: 170 / 700

Versiv Series Cabling Certification Product Family
Technical Reference Handbook
134
Conversely, an unbalanced pair radiates unwanted
electromagnetic radiation. This occurs because the opposing,
differential signals are not equal, so the they are partially
converted to common mode. Common-mode power on a wire
pair produces more radiation than the same amount of power in
differential mode because the common-mode radiation from the
wires does not cancel when the wires are close together.
GPU67.EPS
Figure 60. The Effects of EMI on Balanced and
Unbalanced Twisted Pairs
+1 V
-1 V
+1 V
-1 V
+0.5 V
noise spike
+0.5 V
noise spike
+1.5 V
-0.5 V
When the wires have equal impedance,
EMI adds the same amplitude of noise to
each wire, so no differential voltage is
induced.
When the wires have different impedances,
EMI adds different amplitudes of noise to
each wire. This induces differential noise
that interferes with the data signal.
Unbalanced pair
Balanced pair
+1.0 V
noise spike
+0.5 V
noise spike
+2.0 V
-0.5 V
Differential-mode
signal remains at 2 V
0.5 V spike of
differential noise
added to the signal
+2.0 V
+2.5 V