Probe selection, Introduction, Key factors in selecting a probe – NARDA 8718B User Manual

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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

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