Accuracy Notice; Basis For Near-Field Probe Measurements The H-Field Near-Field Probe - Hameg Instruments HZ530 Manual Del Usuario

Accuracy Notice

Basis for Near-Field Probe Measurements
The H-Field Near-Field Probe
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whenever possible, be made by use of the supplied 1.5 m supply
cable connected to the spectrum analyzer. If this is not possible,
rechargeable batteries should be used. If non-rechargeable batteries
are used, they should be disposed of properly.
The probes may not be used to perform accurate quantitative
measurements. It is not possible to relate the probe measurements
directly to final values of field strength in V/m necessary for certi-
fication tests. The probe kit is intended as an aid for developmental
tests to obtain a qualitative amplitude as a function of frequency.
These values are strongly influenced by the limiting conditions of
the measurement which may change as a function of frequency.
The H-Field probe provides a voltage to the connected measure-
ment system which is proportional to the magnetic radio frequency
(RF) field strength existing at the probe location. With this probe,
circuit RF sources may be localized in close proximity of each other.
This effect is caused by the interference sources which in modern
electronic circuits are of low resistance (relatively small changes
in voltage cause large changes in current). The sources of radiated
interference begin as a primarily magnetic radio frequency field (
H-Field) directly at its origin. Since in the transition from the near- to
the far-field, the relationship between the magnetic- to the far-field
must reach the free-space impedance of 377 Ω, the H-field will
decrease as the cube of the distance from the source. A doubling
of the distance will reduce the H-field by a factor of eight (H = 1/
d³); where d is the distance.
In the actual use of the H-field sensor one observes therefore a
rapid increase of the probe's output voltage as the interference
source is approached. While investigating a circuit board, the
sources are immediately obvious. It is easily noticed which (e.g.)
IC causes interference and which does not. In addition, by use of
a spectrum analyzer, the maximum amplitude as a function of fre-
quency is easily identified. Therefore one can eliminate early in the
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