•Ellipse ratio is ±0.75 dB or better, depending on the model of the probe. The ellipse ratio is the ratio of readings that occur when one rotates the probe around the axis of its handle. Narda calibrates its probes by rotating the probe about its axis and using the mean value to determine the correction factor. If you rotate the probe around its axis and use the mean value, ellipse ratio can be eliminated as a source of uncertainty.
•Isotropic response is the error that occurs when the probe is pointed in different directions. It includes the ellipse ratio plus some additional uncertainties. Although the probes pick up energy from all directions, they are most accurate when pointed at the source of energy. Generally speaking, the isotropic response is no greater than the ellipse ratio providing that the probe is pointed towards the source.
•Calibration uncertainty represents another 0.5 dB.
•The Model 8718B meter has a maximum uncertainty of ±3%.
A good rule of thumb is that the total uncertainty is no greater than ±3 dB when correction factors are not used, providing that the probe is pointed at the source of energy. There are other issues related to field perturbation that can be more significant sources of uncertainty. See Field Perturbation in Measurement in the Applications Booklet.
Making a Measurement
Refer to the Applications Booklet for both general and specific information on making measurements.
Precautions
When making measurements of electromagnetic fields, a potential exists to expose yourself to excessive levels. Approach the source of energy slowly and begin making measurements from a distance at which low field levels exist. Be prepared to evacuate the area immediately if RF field levels in excess of the applicable standard are observed.
28 | Operating the Meter |