R&S HZ-14
Operation
Operating Manual 1026.7767.12 - 01
5
2
Operation
2.1 Magnetic Field Probes
Any changing current in a conductor will cause a small amount of power to be radiated,
it being in effect a transmitting antenna. The amount of power radiated is a function of
the magnitude of the current and the dimensions of the conductor compared to the
frequency of the current. Other conductors in a piece of equipment act as receiving
antennas and have a current induced in them by the radiating conductor. This can
upset the operation of the equipment and where the radiation is very strong other
instruments can be affected.
EMC (Electro Magnetic Compatibility) is the situation where instruments operating in
close proximity do not adversely affect each other, i.e. they are compatible with each
other. Various international regulations exist governing the permitted levels of radiated
emissions and methods of measurement. The probes are not intended to verify
compliance with these regulations; however, they do allow selected areas of different
items of equipment to be compared, and also aid in the tracing of any abnormal levels
of radiation.
Important Notes:
1) When using any of the probes in the set for comparative measurements care
should be taken to obtain repeatable results, i.e. the probe orientation in space
should be the same for each measurement.
2) To correctly measure fields, the magnetic field probes must be orientated for
maximum coupling with the magnetic field, i.e. the end face of the probe top is
perpendicular to the magnetic field. When using the 30 MHz to 1 GHz probe to
measure a concentric magnetic field (the magnetic field around a current carrying
cable is concentric) or to measure any magnetic field whose flux lines have a high
spatial gradient, a difference in output (2 dB nominally) will be observed between
the two probe orientations. Correct orientation of the probe is the one where the
type label is facing away from the cable.
3) The magnetic probes suppress at their outputs any electric field coupling to them.
However, this suppression of electric field coupling is not infinite and therefore care
should be taken when measuring magnetic fields in an environment where very
high electric fields exist.
4) Typical antenna factors [dB (|H|/|V|)] are supplied for the magnetic field probes.
These antenna factors (AF) are frequency dependent for both probes, and are
supplied to enable the calculation of the magnetic field (|H|) linking the probe tip
from the output voltage (|V|) of the probe, e.g.
|H| [dB(A/m)] = |U| (dBV) +AF [dB (|H|/|U|)]
or
|H| [dB(
µ
A/m)] = |U| (dB
µ
V) +AF [dB (|H|/|U|)]
