NARDA 8718B, User Manual

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9 Chapter 3 Probe Selection
Introduction
The 8700 series RF measurement system offers a very broad
selection of probes. The factors that you should consider in
selecting the probe, or probes, best suited for your task are
described in this section.
3
Probe Selection
The probe frequency range should include the frequencies of all
the emitters to be surveyed at one time.
The measurement range of the probe should be adequate for
the field levels that you anticipate, i.e., do you expect strong
fields or weak fields? Probes give more accurate and more
stable readings when they are not used at the extreme low end
of their sensitivity range. Therefore, if you anticipate measuring
very weak fields, select a probe with a lower power full-scale
measurement range to get greater sensitivity. In contrast, higher
power probes give additional safety margins, especially at
microwave frequencies where field strength can change rapidly
with a small change in distance to the source. Select a probe
with a higher power full-scale measurement range if you
anticipate measuring high level fields.
Most standards recommend that you measure both electric (E)
and magnetic (H) fields below 300 MHz (due to the possibility
that measurements may be made in the near field). Since most
experts agree that the electric field poses a greater danger at
lower frequencies due to induced and contact currents that can
occur, the electric field is normally measured first. Higher
frequency measurements are normally made of only the electric
field since measurements will generally be made in the far field.
FREQUENCY
RANGE
POWER
DENSITY
OR FIELD
STRENGTH
ELECTRIC FIELD
VERSUS
MAGNETIC
FIELD
Key Factors in Selecting a Probe