Laplace EMC System: How Does It Work?

Two common problems plaque emission tests: ambient noise and reflections.

Ambient noise comes from FM and TV stations, cell phones, other transmitters and from such noisy sources as nearby computers and other equipment. Reflections result from the electromagnetic waves being reflected from the conductive surfaces and ultimately coming to the receiving antenna. If the reflected signal arrives at antenna in the same phase as the direct signal, the spectrum analyzer will see higher signal than was actually emitted. If the reflected signal arrives in the opposite phase, antenna may register very little signal, while the actual emission at that particular frequency may be substantial. In both cases the test results are invalid. 

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Many companies desperate for efficient EMC solutions buy "typical" EMC system consisting of a spectrum analyzer and an antenna only to find out that the collected results bear no resemblance with the ones done on the same product at a well-equipped laboratory.

In order to reduce ambient interference laboratories use shielded rooms. However, without anechoic treatment, metal walls of shielded rooms act as mirrors and create enormous amount of reflections. Solution to a good repeatable EMC test -- a good anechoic chamber -- may cost over $2 million. Such expenses are justified for test labs and for large companies for whom such investment pays off in a couple of years.

But can a company without $2 million budget perform a test at its premises with a reasonable degree of accuracy? The answer is yes.

Reflections

Laplace EMC System solves reflection problem by simply canceling them. A calibrated Emission Reference Source (ERS) that is a part of a system is placed instead of a tested product and a complete sweep is made. Since each ERS comes with calibration data, the control software knows what it should see in the "ideal" non-reflective environment and makes automatic correction of measured signal. This is done for both polarization of an antenna -- horizontal and vertical. As long as nothing is moved and nothing new is introduced into measurement environment, the test results are virtually reflection-free.

Ambient Noise

Laplace EMC system takes a snapshot of the ambient electromagnetic environment and then subtracts it from the measurement results, substantially reducing the influence of ambient noise on measurement accuracy. A user should still be aware of signals that last only brief time, such as signals from the cell phones, etc.