# Understanding RF Trace Impedance in a KiCad Sensor Hub PCB

DevFeed: [Understanding RF Trace Impedance in a KiCad Sensor Hub PCB](<https://devfeed.tech/articles/home-hardware-part-2-width-matters-35170.md>)

Original publisher: [Read original article](<https://blog.jessfraz.com/post/home-hardware-part-two/>)

Published: 2026-09-10T03:45:45Z

Content type: article

Language: en

Sources: [Jessie Frazelle](<https://devfeed.tech/sources/jessie-frazelle.md>)

Topics: [Hardware](<https://devfeed.tech/topics/hardware.md>), [kicad](<https://devfeed.tech/topics/kicad.md>), [codex](<https://devfeed.tech/topics/codex.md>)

Tags: [codex](<https://devfeed.tech/tags/codex.md>), [hardware](<https://devfeed.tech/tags/hardware.md>), [kicad](<https://devfeed.tech/tags/kicad.md>), [pcb](<https://devfeed.tech/tags/pcb.md>)

## AI overview

The article explains how the author resolved differing impedance calculations for a Sensor Hub's RF layout. It shows that both inner PCB layers contained ground copper, and that the RF trace's reference plane, dielectric thickness, copper thickness, and adjacent ground gap affect the 50-ohm impedance calculation.

## Source excerpt

We're back! Not with rework. This time we're talking about impedance and review. Apparently I can get into a heated argument about a board before it even gets here. In part one, I wrote about using Codex to design my own hardware because I'm sick of Control4, Savant, and the rest of that shit. The useful part wasn't one-shotting a PCB. It was having the agent work through datasheets, compare parts, and check the design. Then I had to notice that the connectors were facing the wrong fucking way. There was more to review. Which board are we arguing about? I was talking through the Sensor Hub's RF layout with Paul, and we were getting different answers for the impedance. This turned into a pretty heated argument, which might have scared some of the other people in the room. Honestly, we were just trying to figure it out. Paul started with this impedance calculator. I kept annoying him because I still didn't understand why we were getting different numbers. Eventually he switched to JLC's calculator, which was what the model was using. I wanted to understand the model's math and compare it with his. The KiCad view was part of the confusion. The connection looked orange, and the second interior layer, In2.Cu, was orange in the layer list. The first interior layer, In1.Cu, was green. So we thought ground was on the second one, and kept arguing about the thickness between layers. Then I realized both interior layers had ground copper, with ground vias connecting across layers. Seeing orange didn't mean the connection was only on that layer. There was ground on the green layer too, right under the RF trace. The model was right! I was just trying to understand what it was telling me. The confusing view, recreated in KiCad. In2.Cu is selected in orange; the green In1.Cu ground is there too. The RF trace is on F.Cu, the top layer. There is 0.1164 mm of insulating material between it and the first inner ground plane. If we used the second inner layer as the reference, we'd be i