A Strange ESP32 RF Bug (and why sockets had to go)

During early builds, I mounted the ESP32-C3 Mini modules using standard 0.1" female headers so they could be easily replaced.

This caused a wierd issue.

ESP-NOW communication was unreliable—some badges would transmit, but often fail to receive broadcasts from others. At first this looked like a software issue, but everything checked out.

Then something odd happened.

If I lifted one side of the ESP32 slightly out of the socket… it started working perfectly.

Plug it back in it was  broken,  lift one side it works

None of the pins on that side were even used.

What was going on?

At 2.4 GHz, small physical details matter more than expected. The most likely causes are:

• Slight ground impedance differences across multiple pins
• Parasitic capacitance introduced by the socket
• Subtle detuning of the onboard antenna due to nearby geometry

In other words, the connector itself was interfering with RF performance.

The fix

For the production badges, I removed the sockets entirely and soldered the ESP32 modules directly to the PCB.

This completely resolved the issue:

• Reliable ESP-NOW reception
• Stable synchronisation across groups

Takeaway

Sometimes the most subtle problems in a system aren’t in the code or the protocol—but in a few millimetres of hardware.

At RF frequencies, “it shouldn’t matter” often means “it definitely matters”.