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# Probes to 6 GHz: Frequency Response and Sensitivity

Loop Probes (100A/B/C): The equation below for Loop Probe Output Power is accurate to within ± 3 dB at frequencies from DC to the 3 dB frequency shown in the table below for each loop probe. The probes are usable to higher frequencies but the sensitivity is uncalibrated above the 3-dB frequency. The first notch in the frequency response of the probes occurs at the first resonance listed in this table. The measured Loop Probe Output Power is plotted

Loop Probe Output Power = [X + 20*log10(B) + 20*log10(F)] dBm

Where B is the rms magnetic flux density in Tesla,
F is the frequency of the received signal in Megahertz
X is a scale factor from the following table:

 Loop Probe Loop Size X 3 dB Frequency First Resonance 100C Large 85.1 50 MHz 500 MHz 100A Medium 67.1 1000 MHz 2600 MHz 100B Small 44.4 3100 MHz >6000 MHz

Electric Field Stub Probe (100D): Stub probes tend to be less repeatable than the above shielded loop probes, due to the presence of common-mode currents flowing on the outer surface of the stub probe or attached cable. As signals are measured, it is common to see a few dB of variation in output power as the user changes their grip on the stub probe or the attached cable. Because of this, the sensitivity of the 100D is not guaranteed. Typical sensitivity of the stub probe is given by the following equation, and is shown in the 100D graph.

Electric Field Probe Output Power = [-113.2 + 20*log10(E) + 20*log10(F)] dBm

Where E is the rms electric field strength, in Volts/meter
F is the frequency of the received signal in Megahertz