Schwarzbeck HFRA 5149 H-Field Transmit Loop VLF / HF

In the VLF-HF frequency range 9 kHz to 30 MHz the magnetic field strength is measured preferably, but often expressed in the unit of the electric field strength as the "fictive E field level" ( dBµV/m).

In the undistorted far-field both units are linked by the characteristic impedance of free space 120 πΩ = 377 Ω. Practical EMC/EMI measurements however are carried out in the near-field zone (D <0.1 λ).

For that reason defined magnetic field sources are required. For Immunity Tests powerful H fields might be needed, but also general tests and measurements at an open site, in screened rooms and in absorber-lined rooms require well-defined powerful H field sources. Magnetic fields in the near-field zone decay with the inverse 3rd power of distance (ca. 18 dB at twice the distance). Even at 1 m distance at 30 MHz the transition from pure near-field to far-field begins, the exponent of degradation gradually reduces from 3 to 1 in the undistorted far-field.

The magnetic loop antenna described here may be operated with up to 100 W input power for short periods and with 30 W continuously. An external 50 Ω power termination with the proper dissipation is required. A 50 Ω 20 Watt termination is part of the scope of delivery of HFRA 5149. It is more than sufficient for the maximum output of laboratory power signal generators.

The HFRA 5149 has a 3/8" camera thread at the box.