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Practical Electronics Editorial offices Electron Publishing (Aust.) Tel +61 2 9939 3295 Unit 1, 234 Harbord Road Email pe<at>pemag.au Brookvale NSW 2100 Web www.electronpublishing.com Australia Address mail to: Electron Publishing (Australia) PO Box 194, Matraville NSW 2036 Australia Advertising enquiries +61 2 9939 3295 pe<at>pemag.au Editor Nicholas Vinen Publisher Nicholas Vinen Digital subscriptions Stewart Kearn Tel 07918 614662 Online Editor Alan Winstanley Web Systems Kris Thain Production Bao Smith Technical staff Tim Blythman, John Clarke Print subscriptions Practical Electronics Subscriptions PO Box 6337 Bournemouth BH1 9EH Tel 01202 087631 United Kingdom Email pesubs<at>selectps.com Technical enquiries We regret that technical enquiries cannot be answered over the telephone. We are unable to offer any advice on the use, purchase, repair or modification of commercial equipment or the incorporation or modification of designs published in the magazine. Questions about articles or projects should be sent to the editor by email: pe<at>pemag.au Projects and circuits All reasonable precautions are taken to ensure that the advice and data given to readers is reliable. We cannot, however, guarantee it and we cannot accept legal responsibility for it. Some projects and circuits published in Practical Electronics employ voltages that can be lethal. Do not build, test, modify or fix any mains-powered equipment unless you fully understand the safety aspects involved and you use an RCD (GFCI) adaptor. Component supplies Silicon Chip Publications may offer kits or other parts for making our projects, but not in all cases. When kits are not available, readers will need to find and source parts themselves. We advise readers to check that all parts are still available before commencing any project in a back-dated issue. 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The laws vary from country to country; readers should check local laws. 2 Volume 54. No. 5 May 2025 ISSN 2632 573X Editorial Ferrite beads are not inductors I often see ferrite beads drawn in circuit diagrams as if they are inductors, with “Lx” designators. While many circuit designers likely realise that they are not true inductors, treating them as such could cause confusion, especially for those reading the diagrams. This might lead them to assume that a ferrite bead is just another type of inductor, when in reality, it serves a very different purpose. Ferrite beads exhibit some inductance – as do most components, including wires and PCB tracks – but their operation does not rely on it. At their simplest, ferrite beads are just a piece of wire passing close to (or through a hole in) a piece of ferrite. Some of the confusion may stem from the fact that ferrite is used as a core material in high-frequency inductors and transformers. However, in those applications, the ferrite core is surrounded by multiple turns of wire to create significant inductance. A ferrite bead has just one or a few turns and thus a relatively low inductance. Ferrite itself is a ceramic material that contains iron oxide. Like other magnetic core materials, it provides a path for magnetic flux, but only up to a certain frequency. Beyond that, ferrite becomes highly ‘lossy’, converting much of the magnetic energy to heat. Ferrite beads take advantage of this property to suppress unwanted high-frequency signals by dissipating their energy, effectively acting as a frequency-dependent resistor rather than an inductor. Unlike an inductor, a ferrite bead does not store energy or resonate. It simply increases its resistance in a targeted frequency range to block unwanted signals. So, rather than thinking of ferrite beads as inductors, it’s more accurate to consider them as a lossy impedance element that selectively dampens high-frequency signals. That distinction matters in terms of circuit design and how we draw them. New telephone number for digital subs & shop items Please note the new telephone number (shown opposite in red). You will have a better chance of getting a hold of Stewart via this new number. The number for print subscriptions (via Select Publisher Services) has not changed. Nicholas Vinen, Electron Publishing (Australia)* Publisher & Editor, Practical Electronics Magazine * a division of Silicon Chip Publications Pty Ltd. Practical Electronics | May | 2025