Atec Narda-8700-8741d-8754D-8760D-8761D - Manual

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Electric and Magnetic Field Measurement
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8700 SERIES PROBES
PROBE SELECTION
The 8700 series system has the most extensive selection of probes available from any source in the world. The
factors that you should consider in selecting the probe, or probes, best suited for your task are:
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 meas-
uring very weak fields, select a probe with a lower power full-scale measure-
ment 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 an-
ticipate measuring high level fields.
Most standards recommend that you measure both electric (E) and mag-
netic (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 only of the electric field since
measurements will invariably be made in the far field.
Flat response probes are the most common. Narda’s patented shaped
frequency response probes read out in Percent of Standard and are par-
ticularly useful in complex, multi-signal environments where exposure
limits are different for the various emitter frequencies and in classified
environments.
The majority of the 8700D series probes have four inch (10 cm) diameter
heads. The minimum measurement distance for these probes is about 4 in
(10 cm) from the outside surface of the probe. Measurements made at
closer distances can result in inaccurate readings due to capacitive cou-
pling. The Models 8721D, 8723D, 8725D and 8783D have two-inch (5 cm) di-
ameter heads that can be used as close as 2 in (5 cm) from the source to the
outside of the probe. These probes are ideal for the measurement of
waveguide leaks. Similarly, the Model 8781D has a one-inch (2.5 cm) di-
ameter head with a flexible shaft that is designed for locating leaks in densely
packaged microwave systems. The 8783D also has a flexible shaft.
Frequency Range
Power Density or
Field Strength
Electric Field versus
Magnetic Field
Flat Response or
Shaped Frequency Response
Size and Minimum
Measurement Distance
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