Designing an EMC Test System FAQs

What’s the most important factor when designing an EMC Test System? +

Unfortunately, there is no one size fits all method when designing an EMC Test System. The most important factor will vary based on the laboratory’s goals, the space available to house the equipment, and the requirements of the testing performed. Considerations should be made if the laboratory needs to test to standards (IEC 61000-4-3, MIL-STD-461, or DO-160), or the goals of the laboratory are to meet requirements for field strength, field uniformity, or frequency ranges.

What are environmental considerations that should be looked at when designing an EMC Test System? +

The chamber’s size where the tests will be performed plays a factor, as the test location can vary from a small reverberation chamber to a large semi-anechoic chamber. These matters can affect parameters such as cable loss, test distance, and required amplifier power. In addition, the installation space should always contain adequate power, cooling, and footprint for the equipment being installed.

How can we set ourselves up to be able to grow our testing capabilities over the years? +

When making any large investment, it is always important to consider how that investment will continue to work for you as your needs change. Although standards within the industry are always evolving, it is important to educate yourself on the industry’s future requirements with IEEE meetings and working groups and team up with partners that are doing the same. Working with the right partners to enhance your knowledge and education to understand the future testing requirements and how to angle yourself to be prepared is the best way to align your future goals with your investment.

Can a GTEM cell be cost-effective for testing radiated immunity/emissions pre-compliance? If so, why? +

Yes. GTEMs are significantly less expensive than a chamber, so if pre-compliance capabilities are all that is required, this cost reduction can be a compelling driver. This component is, of course, if the EUT is small enough to fit into a GTEM. Also, EUTs with cabling can pose problems inside a GTEM as repeatability with cable positioning becomes a concern.

What is the rationale behind determining the required amplifier power to perform the test? I have often heard that I will need more power than I think. +

When determining your required amplifier power, it is recommended to accommodate for the unexpected as, in this industry, there is a lot of room for unexpected effects. Therefore, taking a conservative approach in determining your power requirements is suggested.

In a radiated immunity test setup, is there a way to minimize “amp drift,” where the amp’s power output changes over time with the same input signal? +

To begin with, consider the type of amplifier you are using in your setup. Amplitude drift is rarer with solid state power amplifiers (SSPA) than with Traveling Wave Tube Amplifiers (TWTA). Next, warm up your amp. Sometimes amps (even SSPAs) need some time to warm up to stable operation. The effect is much less pronounced in SSPAs than in TWTAs. If, after warming up, the amp is still not performing to the level expected, the signal generator drive could be adjusted to accommodate for a decrease in gain. Using a directional coupler, one can calibrate the forward power required to produce various fields and adjust drive levels to achieve the required forward power.

If amplitude drift becomes a concern, the power measured from the directional coupler can also be used to detect these anomalies.