Overview
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 π? = 377 ?. 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 ? power termination with the proper dissipation is required. A 50 ? 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.
Technical Data | |
Frequency Range (nominal) | 9 kHz – 30 MHz |
SWR | < 2 (0.02 – 20 MHz) |
Connectors | 2 x N female |
Ext. termination | 50 ? |
ACCESSORY | 50 ? / 20 Watt |
Polarisation vertically mounted | vertically (fictive E field) |
Directive Pattern | 2 x 90° half power vertical axis |
Dimensions | 515 x 585 x 80 mm |
Cross section Fully shielded | Ø 20 mm |
Material of the housing | Aluminium |
Weight | 1250 g |
Mounting support camera thread | 3/8“ |