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Latest News in Testing, Inspection and Certification

NTS News Center - Latest News in Testing, Inspection and Certification

NTS Quick Guide to Reverberation Testing

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Inside the RF chamber

A reverberation chamber (mode tuned/mode stirred chamber) is a shielded enclosure or resonant cavity for RF testing which is statistically isotropic, random polarity, having RF uniformity within specified limits. Typically it has a paddle (or tuner) which stirs up the field, randomizing the boundary conditions. Mode tuned is where the paddle is stepped to a position and then RF is applied for a dwell time sufficient to exercise the equipment. Mode stirred is when the paddle is continually turned with RF energy applied for a full paddle revolution. Reverb chambers are useful for radiated susceptibility, radiated emissions (total radiated power), shielding effectiveness, and many other troubleshooting scenarios.

The benefits to reverberation testing are numerous. RF is applied to all exposed sides of the device under test (DUT) during a full 360° turn of the paddle, instead of a single side. For direct illumination testing, many standards require the all apertures of the DUT to be illuminated. On complex items this can be difficult – even impossible. Window effects testing, required when applying direct illumination, is not required during reverb testing because the field intensities are constantly changing. SAE ARP 5583 states that the reverb is the recommended and preferred method to show compliance for large and/or complex Level A (flight critical) systems. Test repeatability is much easier to obtain in a reverb chamber with proper processes, and running the test is much less complex than a single aspect angle test. Antenna distance, aim (focus), 3 dB beam width, location of the field probe, EUT layout, and location of the EUT in the working volume are all less of a factor in the repeatability of test.

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A view from outside

You should know if reverberation testing is right for your program. Reverb chambers are random in polarity which makes it challenging in determining directivity of RF energy. Testing multiple field levels on a system, such as outside the pressure vessel level and inside the pressure vessel level, can be difficult; all equipment in the chamber is exposed to the same field. There are limitations on pulse width due to a high Q (efficient) chamber having large amount of stored energy. If you have small, simple equipment, single aspect angle tests may be faster and sufficient for test coverage. There are ways to compensate for each, and an NTS engineer can help with suggestions or assist you with a test plan.

Both direct illumination and reverberation test methods are acceptable paths to certification. They both have benefits and drawbacks that champion each as a test method. Fortunately, NTS has the ability to test in both methods and the engineering expertise to support your path to certification.

For more detailed information about reverberation testing at NTS Rockford, Fullerton, Plano, Tempe, or Boxborough, call 800-270-2516 or email us at sales@nts.com. Request a quote today!

New Reverberation Chamber at NTS Rockford Achieves Greater than DO-160 Category L Levels!

MainImage_558We are pleased to announce our newly-added second reverberation chamber, coupled with state-of-the-art amplifiers, achieves greater than DO-160 Category L levels from 100 MHz to 18 GHz. Test frequencies as high as 40 GHz are now possible at NTS Rockford! This 12’ × 20’ × 10’ chamber has a test volume of over 438 cubic feet or 12.42 cubic meters and a 4’ × 7’ door.

The chamber and its adjacent 10’ × 10’ ground plane are configured for convenience and efficiency. Customer support equipment is staged on the ground plane, and the chamber’s computer-controlled horizontal stir assembly is mounted unobtrusively high on the rear wall. Both the chamber and ground plane are equipped with filtered AC and DC power: 28 VDC, 480 VAC and 120/208 VAC at 60 Hz, and 115 VAC at 400 Hz. Nonstandard power is also
available upon request.

MainImage_558_2This chamber’s extremely large usable test volume (over 438 cubic feet) allows for testing multiple-LRU systems. It has field densities capable of achieving peak fields up to 15,000 V/m. Like other NTS Rockford EMI chambers, this reverberation chamber is drive stand-adaptable and can be mated to a motor drive for rotating equipment. An efficient chamber layout coupled with test methodology ensures lean test execution.

If you are interested in learning more please contact our EMC Engineer Scott Carlson directly at scott.carlson@nts.com or call (815) 315-9250, ext. 179. We look forward to sharing this great new offering with you!