Noise from Raspberry Pi, Arduino Detection and Mitigation

Taming Differential-Mode Noise from SBCs in the Shack

How to detect it, measure it, and reduce it without turning your station into a Faraday cage.

Single-board computers (SBCs) like the Raspberry Pi and microcontrollers (MCUs) like Arduino have transformed ham radio projects: automation, APRS iGates, digital modes, rotator control, remote receivers, antenna switching, and more.

The downside is less visible but very real: differential-mode noise. This noise is conducted inside wiring itself and can land squarely in the middle of HF and VLF reception. Clamp-on ferrites often help with common-mode problems, but differential-mode noise can stubbornly remain—especially when it is injected directly between supply rails or across signal pairs.

This article explains what differential-mode noise is, what it looks like on the air, how to measure it with tools many hams already have, and how to mitigate it effectively.

Differential-Mode Noise vs Common-Mode Noise

Common-mode noise

• The same unwanted RF current flows together on multiple conductors.
• Cables behave like antennas and radiate efficiently.
• Clamp-on ferrites and common-mode chokes are often effective.

Differential-mode noise

• The unwanted signal exists between two conductors, such as +5 V and GND.
• It originates from real switching activity, clocks, and fast edges.
• Imperfect geometry and parasitics convert part of it into radiating common-mode current.

Key takeaway: Differential-mode noise is the source; common-mode radiation is often the result.

Where Differential-Mode Noise Comes From

• DC-DC converters – Switching ripple and harmonics across Vcc and GND.
• High-speed clocks and PLLs – Spectral combs and load-modulated spurs.
• PWM and fast GPIO edges – Buzzing and broadband emissions.
• USB, HDMI, Ethernet – High-speed interfaces producing HF-visible harmonics.

Typical On-Air Symptoms

• Narrowband spurs at fixed frequencies.
• Evenly spaced “combs” tied to switching or periodic activity.
• Noise that appears only when the device is powered or under load.
• Clamp-on ferrites help only marginally.
• Noise seems to come from cables rather than the board itself.

How to Detect and Measure It

Establish a baseline first. Measure your receiver noise floor with the device off, on, and under load.

SDR sniffing

• Use a small near-field loop with an SDR.
• Compare idle vs load conditions.
• Move the probe along power, USB, HDMI, and GPIO cables.

Portable receiver walk-around

• Tune to a quiet spot or known spur.
• Move close to suspect cables and note peaks.

Oscilloscope checks

• Measure power rails and key I/O lines.
• Use very short ground connections.

Mitigation Strategy: Fix It in Layers

Layer 1: Power system

• Use a clean supply; avoid cheap wall warts.
• Add LC or π filtering close to the device.
• Twist and shorten DC power leads.
• Test with battery power for receive-only setups.

Layer 2: Cables

• Use twisted pairs for signals and DC.
• Add series beads or resistors per conductor.
• Use shielded cable with proper termination.

Layer 3: I/O control

• Slow down what doesn’t need to be fast.
• Physically separate digital devices from RF front ends.
• Use USB isolators where appropriate and compatible.

Layer 4: Grounding and bonding

• Avoid unintended return paths.
• Favor short, wide bonding over topology theory.
• Measure bonded vs floating configurations.

Layer 5: Shielding

• Use metal enclosures only after reducing the source.
• Treat every cable as an RF entry and exit point.
• Disable unused high-speed interfaces such as HDMI.

Quick Checklist

• Test with a quiet supply or battery.
• Twist and shorten DC wiring.
• Add input filtering at the device.
• Increase physical separation.
• Disable unused high-speed interfaces.
• Only then add shielding and ferrites.

Don’t Blame the Board—Blame the Integration

SBCs and MCUs are optimized for cost and convenience, not ultra-quiet RF environments. In most cases, interference is caused by power, cabling, and return-current management—not the board itself.

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