KC R20 Near Field Probe kit includes three different size passive magnetic field probe. It has flat frequency response in the 30MHz to 3GHz, used to measure the magnetic field during the developmental stages.
They are also sensitive at low frequencies. The probe diameter of three probes are 20 mm, 10 mm, and 5 mm. The larger probe has high sensitivity, but low directional resolution. Instead, smaller probes have low sensitivity but high directional resolution.
Usually, we use the large one to detect where the interfering source is roughly located, and then use a smaller probe to narrow the search range, and identify the source of the interfering magnetic field in the electronic module step-by-step.