AEMC® – Reducing Noise Voltage/Broadband EMI In Shielded Cables


In this short video, we demonstrate the importance of properly grounding the shielding in a cable.
This helps minimize the presence of stray noise voltage being generated in the cable
due to the proximity of live electrical lines. For our demonstration we have placed a length
of shielded cable adjacent to an extension cord plugged into a common electrical outlet.
We have connected one end of the cable conductor to a digital multimeter. For our first measurement,
we will leave the cable shielding ungrounded. As you can see, the noise voltage being generated
within the cable is over 6 volts, a voltage that could potentially corrupt any data sent
through the cable. Now we’ll connect the cable shielding to
ground. Notice that the noise voltage has dropped to around 100 millivolts, nearly two
orders of magnitude lower than our previous reading. In other words, grounding the shielding
has reduced noise voltage within the cable by around 98%. Note that only one end of the shielding should
be grounded. The addition of one or more other grounding points could result in a ground
loop that could compromise the efficacy of the ground. This concludes our demonstration of reducing
noise voltage in shielded cable. Be sure to check our YouTube channel for instructional
videos on other topics in electronics, including the many products offered by AEMC.

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