Ferrite beads are awesome, and I agree that everyone involved with computing and electronical things should have an assortment of them nearby. They can fix problems.

And yeah, we're pretty close to the limits. We always have been, though: At all points on the timeline of digital electronics, we've been pushing speeds to be as fast as we can manage today. But tomorrow (and the next day, and the day after that), we'll solve more of the problems and yet-again make it even faster.

Which brings us back to...ferrite beads, and problems.

I got introduced to Monoprice back when HDMI was still new and somewhat finicky, when stores like Best Buy were fond of selling $180 HDMI cables (and even Wal-Mart wanted something like $60). In that crazy world, Monoprice was the place to buy inexpensive cables that worked.

And it was clear that HDMI was the future, so I placed an order for a half-dozen or so different-colored HDMI cables with ferrites pre-installed near each end.

They showed up, and... they barely worked. They were glitchy, touchy, and intermittent. I was frustrated, and I felt like I'd made a poor decision that cost me money instead of saved me money. In fact, I was rather pissed off by all of this.

With nothing to lose, I used a knife to cut away the plastic overmolding on the ferrites on one of the cables that was being particularly problematic. And then I smashed those ferrites with a hammer.

With the ferrites thus-removed, the cable immediately began working perfectly. It was glitch-free. I couldn't get it to misbehave even if I tried. I repeated this with all of the other cables from that order and they all started working perfectly, too.

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So, ferrites. Their presence adds a little bit of series-mode inductance. And that's something that can be useful. It slows down the edge of things like transient voltage spikes. And since the spikes are transient, slowing their rise-time in this way reduces their bandwidth and peak amplitude. Adding a snap-on ferrite bead can be enough to turn a problematic data bus into a well-behaved data bus.

But! They're just dumb hunks of minerals. They're indiscriminate. They can't distinguish betwixt the bad signals and the good signals -- everything is affected. So while ferrites can be useful in a fight against unwanted noise, they can also be destructive of the signals that we're trying to use.

They're good to have available, but they're also not necessarily something that someone should go forth and attach to every cable they find. If there's no problem that needs solved, then there's no solving to be done.

(These I days I make it a point to actively avoid buying cables that have ferrites pre-installed, both professionally and at home. But I've got a stash of snap-on ferrites in the top drawer of the toolbox just in case; it's good to have options.)

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