Tutorial 7
Keysight 34970A/34972A User’s Guide 271
Shielding Techniques
Shielding against noise must address both capacitive (electrical) and inductive
(magnetic) coupling. The addition of a grounded shield around the conductor is
highly effective against capacitive coupling. In switching networks, this shielding
often takes the form of coaxial cables and connectors. For frequencies above 100
MHz, double-shielded coaxial cable is recommended to maximize shielding
effectiveness.
Reducing loop area is the most effective method to shield against magnetic
coupling. Below a few hundred kilohertz, twisted pairs may be used against
magnetic coupling. Use shielded twisted pair for immunity from magnetic and
capacitive pickup. For maximum protection below 1 MHz, make sure that the
shield is not one of the signal conductors.
Separation of High-Level and Low-Level Signals
Signals whose levels exceed a 20-to-1 ratio should be physically separated as
much as possible. The entire signal path should be examined including cabling
and adjacent connections. All unused lines should be grounded (or tied to LO) and
placed between sensitive signal paths. When making your wiring connections to
the screw terminals on the module, be sure to wire like functions on adjacent
channels.
Recommended Low-Frequency Cable:
Shielded twisted pair
Recommended High-Frequency Cable:
Double-shielded coaxial cable
LO
HI
LO
HI
Twisted Pair Shield
Center Conductor
Shield Foil
Shield Braid
PVC Jacket
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