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Interference Technology

For EMI / EMC Engineers

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Designing and Selecting Filters: Using Soft Ferrite Cores

 

All inductors (L) suffer from RF resonances, and are only effective in filters at frequencies not far above their first (parallel) resonance (see section 1.8.1 of [7]). But so-called ‘soft ferrites’ behave resistively at RF, and the resulting lack of RF resonances helps make filters that use them have better and more predictable performance at RF. For example, a typical small … [Read more...]

Designing and Selecting Filters: Differential Mode and Common Mode

 

Differential-mode (DM) and Common-mode (CM) Wanted signals are always DM: they flow along the ‘send’ conductor, and flow back along the ‘return’ conductor(s). In single-ended signalling, all the return currents share a common conducting structure, usually the 0V of the DC power distribution system. In balanced (or ‘differential’) signalling there is a dedicated conductor for … [Read more...]

Designing and Selecting Filters: The Importance of RF Reference

 

The Importance of the RF Reference The RF Reference is the node on a circuit’s schematic that we define as our reference voltage when designing an RF circuit or measuring its performance. For the most cost-effective EMC, all circuits (digital, analogue, switch-mode, etc.) should now be designed using RF techniques. It is common practice to call the RF Reference ‘earth’ or … [Read more...]

Designing and Selecting Filters: How Filters Work

 

Ignoring all the poles and zeroes in the filter textbooks: filters work by creating an intentional discontinuity in the characteristic impedance of a current path, reflecting radio frequency (RF) energy away from a protected circuit, or absorbing the RF energy (converting it to heat) – rather like a shield does, as will be described in Part 4 of this series. The greater the … [Read more...]

5 Ways Signal Noise Can Impact Electrical Equipment

 

Accurate data acquisition is often critical in various engineering and technical projects. However, a pervasive yet often-overlooked issue that arises in the system is signal noise. This unwanted electrical interference, originating from multiple sources, can corrupt measurements, hinder communication, and compromise equipment integrity. Recognizing the Symptoms: … [Read more...]

Plugging into a Power Source 93 Million Miles Away

 

Harwin Gecko-MT 1.25mm pitch Mixed Layout Connectors Connect with confidence with Harwin’s Gecko-MT range; the smallest and lightest mixed-layout connector available for high-reliability applications. The Gecko-MT range combines the 1.25mm pitch Gecko signal connector system with mixed technology layouts, which adds 10A power contacts to the range, providing additional … [Read more...]

Selection of LC Filters to Ensure HEMP Protection of Electronic Equipment

 

According to military standards, passive electromagnetic LC filters of HEMP are recommended for use in all kinds of special-purpose electronic equipment. Experience gained by military specialists is usually employed when developing HEMP protection means and measures for civil equipment. Does it make sense to use extremely expensive and bulky HEMP filters for civil equipment? … [Read more...]

Doing Things That Usually Do Not Work

 

“If you’re not making mistakes, then you’re not doing anything.” — John Wooden Over the years, I have seen several things that make me scratch my head. Many of them are things I have done (there, I admitted it). I would like to look at these situations to (maybe) help not to make the same mistakes. So, to be clear: Do not do these things. Concerning Shielding One would … [Read more...]

EMC Confidence Checking

 

I was recently working with a manufacturer of stand-alone ticket machines, who had big problems with Ethernet-related emissions. Long story short – it was the Ethernet hub they had incorporated in their machine. They had assumed that all CE-marked Ethernet hubs would be equally good for EMC, and they had several different types lying around their design department. We tested … [Read more...]

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