Using an EMC Test System - FAQ

Using an EMC Test System

  • What do you recommend when performing a radiated immunity system’s calibration in terms of frequency step size? Is it dependent on the EUT or the standard?
  • Due to variables in the flatness of equipment and anechoic chamber inconsistencies, it's best to calibrate the specific frequencies that will be tested. Refer to the test standard to ensure that this is the approach specified.
  • What is the definition of spot size?
  • Spot size, coverage area, beamwidth, or coverage width all mean the same thing. An antenna will cover the area or width when placed a specific distance away from the test object and related to its 3 dB beam width.
  • Spot size, when given as a length ("1.5 meter spot size"). Is that length a radius or a side of a square?
  • 1.5 meters by 1.5 meters.
  • Have you ever heard of any reputable EMC labs wrapping cables in aluminum foil to prevent auxiliary equipment from emitting EMI into the EUT or the measurement equipment?
  • When running a test, this may be done if the EUT is not susceptible, but the auxiliary equipment is. To mitigate this, a technician or customer may wrap cables in foil, apply ferrite beads, or rearrange the auxiliary equipment setup to prevent the susceptibility from continuing. This precaution is sometimes done as a mitigation step to determine if cables are culprits for excess radiated emissions. It is important to note that if foil is required as a solution to mitigate immunity or emissions, equivalent shielding will be necessary for the EUT’s actual installation.
  • In a radiated immunity test setup, do you recommend having the field probe in the test field for measuring the field strength during the test? Or is the effect of the EUT going to make the field probe measurement useless?
  • This measurement will be defined in the test standard applied. For MIL-STD-461 testing, the standard defines the placement of the field probe during actual testing. For IEC 61000-4-3 and DO-160 testing, the field probe is utilized during a pre-test field calibration where the forward power to achieve the field is recorded and then played back during testing.
  • I was testing radiated immunity and meeting field requirements. The following day, after nothing had changed, I was no longer meeting field requirements. What happened?
  • Several factors could cause you to have issues. Some possibilities are the RF switches could be routed incorrectly, amplifiers were not switched into operate mode, or some other issues could result in a loss of field. Our recommendation is to contact the applications engineers where you purchased your system. AR application engineers are always available to assist in troubleshooting efforts for systems developed by AR at
  • When is software automation necessary vs. not?
  • Some test standards require software automation, but not always. If the standard requires graphical data for reporting purposes, then software automation is recommended. If tabular data is specified, then software automation is not necessary. If it is not specified, then you can decide on which will make the test run faster.
  • If I buy an EMC Test System from AR, how will I know how to use it?
  • Along with the installation, AR will send Systems Engineers to educate your personnel on how to use the system.