8.9.4 Spatial Sampling And Probe Position
Measurement locations should represent places that people can occupy and should include predicted or observed maxima. A preliminary scan can locate spatial peaks, after which measurements can be made at the points, heights, grid, area, or projected-body positions required by the applicable method. The number and spacing of samples must be sufficient to characterize nonuniform fields and to perform any prescribed spatial averaging.
Probe position, orientation, separation from the source, and distance from nearby objects should be controlled and recorded. The sensor dimensions should be small enough for the required spatial resolution, especially in the near field. Nonconductive supports, remote readout, and adequate operator separation should be used where necessary to reduce field perturbation. A measurement should not be taken with the operator's body occupying the space intended to represent an unperturbed field.
8.9.5 Environmental And Measurement-System Perturbation
Buildings, towers, vehicles, ground surfaces, fences, vegetation, and other objects can reflect, absorb, or concentrate RF energy. Multipath can produce substantial variation over short distances, so a single convenient point may not represent either the maximum or the spatial average. Moving people, vehicles, doors, and equipment can also change the local field during a survey.
The probe support, operator, and connecting cable can perturb the field or introduce common-mode response. Cable routing should be controlled, losses and connector condition verified, and fiber-optic or other low-perturbation links used where appropriate. Temperature, humidity, precipitation, and other conditions should be kept within the instrument specifications and recorded where they can affect repeatability or propagation.
Unexpected spatial variation should be investigated by repeating measurements and changing one factor at a time, such as probe position, operator distance, cable route, or nearby object location. This helps distinguish a real field maximum from a measurement-system artifact.