Narda's EA5091 electrical field probe provides frequency shaping to match the FCC standard for a controlled / occupational environment and the results can be displayed in "% of standard." Isotropic measurements and precision readings are available without knowing the emitted frequency.
The probe contains 6 dipoles- 3 diode based and 3 thermocouple based dipoles. The correctly tuned overlap of two dipoles, one acting as a high pass filter the other as a low pass filter, provides a frequency sensitivity that mirrors a particular standard. Testing for compliance to that standard is easier without the requirement of knowing the frequency.
The goal in designing and manufacturing a traditional, “flat” frequency response probe is to make the probe equally responsive to energy at every frequency within its rated frequency range. In contrast, Narda’s patented shaped frequency response probes are designed and manufactured so that their sensitivity mirrors a particular standard (or guidance) as closely as possible.
For example, many of the major guidances and standards in the world set E-field limits for maximum human exposure at 614 V/m (1000 W/m2) at lower frequencies (~1 MHz). At frequencies of 30 to 300 MHz the limits are typically much less, 61.4 V/m (10 W/m2), a difference of 20 dB (100 times the power). A shaped frequency response probe designed for such limits is 100 times more sensitive in the 100 MHz region, than at 1 MHz.
If you were performing a survey of a site with a flat frequency response probe that has both of the above frequency ranges and your survey indicated 137 V/m (or 50 W/m2), it would be difficult to determine if the site was out of compliance without turning one of the emitters off. Again, given the example above, the site could be generating anywhere from 5% to 500% of the human exposure limit. There are many sites with multiple emissions (rooftops, flight lines, broadcast towers) that have emitters at different exposure limits.
Narda EA5091 Features
Measurement range: 0.5 to 600% of FCC "Occupational/Controlled limits"
Linearity: +/- 3 dB (0.5 to 6%)
+/- 1 dB (6 to 100%)
+/- 2 dB (100 to 600%)
Freq sensitivity: +/- 2.0 dB from Standard