Estimated reading time: 5 minutes

Elementary Mr. Watson: Running the Signal Gauntlet

If you’ve ever run a military obstacle course, you know it’s less “fun fitness challenge” and more “how can we inflict as much pain in the shortest time possible?” You start fresh—chest out, lungs full of confidence, thinking you might even look good doing this—and 10 seconds later, you’re questioning all your life choices.

From that first obstacle of a high wall, you hit the dirt for the low crawl under barbed wire and immediately discover two things: gravel and elbows become sworn enemies, and that “low” crawl is an effort to turn a human into a two-dimensional figure. Soon, you’re spitting out sand, twigs, and maybe a little of your pride.

Then comes the rope swing. In theory, it’s a graceful arc over a water pit. In reality, it’s a comedy reel in which you cling for dear life, miss the perfect release point, and perform a slow-motion belly flop into three feet of cold, muddy water. You now experience the rest of the course in wet socks and boots that feel like they’ve been filled with lead shot.

At the finish line, you’re no longer the elite athlete you imagined; you’re a battle-worn survivor. That’s because a military obstacle course isn’t a random pile of hazards; it’s engineered to test your every capability. It also exposes weaknesses. If you falter in any skill, the course will find it.

A PCB functions much the same way for signals, with its own obstacles to overcome. However, most PCB designers don’t instinctively think of a PCB as a controlled environment. Rather, they view it as a constructed connection—just make the connections from point A to point B. The root cause of that problem lies in the CAD tools.

On the screen, everything looks flawless: perfect lines and crisp color. But look closer, and your PCB is a patchwork of uneven terrain, changing widths, inconsistent dielectric properties, and electromagnetic crossfire—its own military-grade obstacle course complete with levels of difficulty that would make even the most brutal drill sergeant raise an eyebrow.

I’d even say the PCB is an electromagnetic ecosystem. Some ask, “Isn’t a PCB just a flat sheet of fiberglass with some copper glued on it?” No. Fiberglass is not flat. Every part—traces, vias, planes, components, solder mask, and the spaces between the different layers and materials—plays a role in shaping the environment your signals have to survive in. Additionally, nothing exists in isolation. A tiny change in one area can ripple through the entire system.

When you look at the PCB like signal integrity does, you stop seeing pretty copper traces and the terrain the signal has to survive. From the moment a signal launches, it’s all good—sharp edges, perfect timing, full of energy, and practically whistling as it leaves the source. It’s the PCB equivalent of a fresh-faced recruit jogging to the starting line thinking, “This won’t be so bad.”

Like an obstacle course, the signal launches off the starting line, running down that first trace. It hits the first obstacle—the high wall—of what will become many impedance mismatches at full speed, only to realize it can’t pass cleanly through. Instead, it has to scramble, clawing at the surface, burning precious energy. While it’s struggling, a whole chunk of energy doesn’t make it. That portion bounces back the way it came, ricocheting toward the source as a reflection, ready to cause trouble for the next recruit on the starting line.

From the signal’s perspective, this isn’t just tiring; it’s destabilizing. The smooth, consistent rhythm from the starting line is now disrupted. It’s breathing harder, its edges are less crisp, and it knows there are more obstacles ahead. The wall might be behind it now, but the loss here will echo (literally) through the rest of the run.

No time to wallow in self-pity; the next obstacle awaits: low crawl under barbed wire. Now, the signal drops to the ground, forced into a tight crawl. The barbed wire of crosstalk—the electromagnetic mutterings—hangs overhead with sharp jabs from nearby traces. Every inch forward brings a risk: lift its head too high and the barbs bite; stray too far sideways and it’s clipped by the chatter of an aggressive neighbor net.

The air is thick with interference. Parallel “runners” on adjacent lanes shove at its sides, sending jolts of unwanted energy into its path and distorting its form, pulling it further from its clean, confident starting shape. Let’s say the skin effect kicks in—the signal is stuck hugging the surface, wishing it could stretch out without getting zapped. By the time it scrapes through to the other side, the signal becomes hunched, jittery, and carries a noise it never asked for.

Just when the signal thinks the course has leveled out, it hits the dreaded mud pit. This is attenuation, the slow, relentless drag that doesn’t trip it outright but saps strength with every step. At first, the surface looks harmless, almost inviting, but the instant its feet touch, forward motion turns into a slog. Each stride grows heavier. The copper’s resistance tugs at it like thick mud clinging to its boots, while the dielectric loss is the pit, quietly swallowing a little more energy with every move forward. Progress becomes more difficult, the pace slows, and the effort needed for each step seems to double.

At the end, a signal’s journey across a PCB is only as safe as the environment we build for it. In a well-balanced electromagnetic ecosystem, the obstacles are small and predictable. The signal might break a sweat, but it crosses the finish line strong and ready for work. In a toxic, uncontrolled environment, every hazard becomes amplified. Walls are higher, the barbed wire hangs lower, the trapdoors drop deeper, and the mud pits stretch for miles. By the time the signal reaches the receiver, it’s been pushed, slowed, and battered into something unrecognizable.

Unlike an obstacle course runner, it won’t limp away to train for next time; it will simply fail, and take your design down with it.

This column originally appeared in the September 2025 issue of Design007 Magazine.