Publicité
Tutorial
7
At frequencies above a few kilohertz, a coaxial cable's shield becomes inductive,
rather than resistive, and the cable acts as a transformer. When this happens, it
tends to force the shield and center-conductor currents to be equal but opposite.
For any voltage drop in the shield due to I
, there is a similar drop in the center
GND
conductor. This is known as the balun effect and it reduces ground loops at higher
frequencies. Note that lower shield resistance causes the balun effect to become
more of a factor at lower frequencies. Therefore, coaxial cables with two or
three-braided shields are much better than those with single-braided or foil
shields.
To reduce errors due to ground loops, connect the function 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 function generator and the load are connected to
the same electrical outlet to minimize further differences in ground potential.
Keysight 33210A User's Guide
357
Publicité
