Differential Noise from Raspberry Pi, Arduino Detection and Mitigation

Single-board computers like the Raspberry Pi and microcontrollers like Arduino have revolutionized ham radio automation, APRS iGates, digital modes, rotator control, and more. But beneath their GPIOs and blinking LEDs lies a less visible problem: differential-mode noise that can wreak havoc on nearby receivers—especially in HF and VLF setups.

This article unpacks the nature of this noise, how to measure it, and how to reduce it without wrapping your shack in tinfoil.

What Is Differential Noise?

Unlike common-mode noise (which rides the outside of cables and can often be choked out with ferrites), differential-mode noise exists between two conductors. In the case of SBCs and MCUs:

  • It appears between Vcc and GND, or
  • Across data lines (e.g. SDA/SCL, USB D+/D−, UART TX/RX),
  • Often emitted by DC-DC converters, PLL clocks, and PWM outputs inside the device.

These signals are legitimate from the device’s perspective, but from an RF standpoint, they inject conducted noise directly into power and signal cables, which may then radiate.

Typical Symptoms

  • Narrowband noise at fixed frequencies (e.g., 100 kHz harmonics, USB 2.0 at 480 MHz, PWM buzz)
  • Repeated spikes every 66.7 kHz (typical for buck converters switching at ~133 kHz)
  • Noise appears only when the Pi/Arduino is powered, and often tracks with CPU load
  • Noise persists despite ferrite chokes on cables, because it’s not common-mode
  • It radiates from cables, not the board itself—cables become efficient antennas

How to Detect It

Use an SDR

A USB SDR (e.g. RTL-SDR, Airspy, SDRplay) makes a perfect near-field probe.

  • Run your Pi or Arduino with your normal application
  • Tune around HF, VHF, and UHF bands
  • Look for harmonics or digital combs that correlate with CPU activity or I/O

Portable Receiver

Walk a portable receiver or handheld around the workspace:

  • Tune to suspect frequencies (e.g. 3.579 MHz, 7.2 MHz, 10.7 MHz, 14.2 MHz)
  • Move closer to DC cables or GPIO lines—noise will spike when near a culprit

Oscilloscope

If you have one, probe:

  • Power rails (Vcc to GND)
  • UART TX/RX or I2C lines
  • Observe square waves, spikes, or repetitive bursts in the time domain

Mitigation Strategies

Differential noise is stubborn because it’s not removed by simple clamp-on ferrites alone. Here’s a layered approach:

Power Supply Isolation

  • Use linear regulators or filtered DC rails
  • For USB-powered devices, insert a USB isolator (especially for SDR or soundcard interfaces)
  • For GPIO-driven peripherals, use opto-isolators or DC-DC converters with galvanic isolation

Cable Filtering

  • For DC lines: Use LC filters close to the Pi/Arduino (e.g. 10 µH + 100 µF ceramic cap on Vcc)
  • On data lines (UART, I2C): Add ferrite beads + RC damping or use twisted pairs

Grounding Discipline

  • Avoid ground loops between your Pi/Arduino and other gear
  • If possible, float the system or use a star ground with a single point-to-chassis tie
  • In receive-only setups, consider using the Pi or MCU with battery power to break conducted paths

Shielding (If Nothing Else Works)

  • Enclose the SBC/MCU in a metal case (preferably grounded)
  • Ensure filtered feedthroughs or ferrite cores on every cable entering/exiting the box
  • Don’t forget to shield displays (e.g. Nextion, HDMI screens) which are often worse than the CPU itself

Don’t Blame the Pi – Blame the Integration

Raspberry Pi and Arduino boards aren’t designed with RF hygiene in mind. But the problem usually lies in how we power and connect them, not the boards themselves.

With proper filtering, grounding, and isolation, these devices can live peacefully even in sensitive SDR and ham radio environments.

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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.