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Chapter 5 Tutorial
Ground Loops
4
5
At frequencies above a few kHz, a coaxial cable’s shield becomes
inductive, rather than resistive, and the cable begins to act like a
transformer. When this happens, voltage drops in the shield due to I
GND
tend to be offset by equal voltages in the center conductor, thereby
reducing the effects of ground loops at higher frequencies. Coaxial cables
with two or three braided shields are much better than those with single-
braided or foil shields because they have lower resistance and therefore
become transformers at lower frequencies.
To reduce errors due to ground loops, connect the waveform generator to
the load using a high-quality coaxial cable and ground it at the load
through the cable’s shield. If possible, make sure the waveform generator
and the load are connected to the same electrical outlet to minimize
further differences in ground potential.
Be aware that the outer shells of the Sync and Modulation In connectors
are connected to those of the main output connector(s). Cables attached
to Sync and/or Modulation In are therefore potential sources of ground
loops. Also be aware that attempting to drive those connector shells to
different voltages can cause high current to flow through the instrument,
possibly causing damage.
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