Troubleshooting Man-Made Noise on Hotspot, Transceiver PCB's and Devices (VHF/UHF)

Unwanted noise on SVXLINK Hotspots or similar devices can come in many forms: a persistent 50/60 Hz hum, wideband hash, or pulsing interference. These types of noise are often man-made and stem from switching power supplies, poor shielding, or environmental coupling. This guide outlines the key causes and how to isolate or resolve them.

Our hotspot with enclosure provides a reasonable degree of shielding against typical sources of man-made noise.

The transceiver version is fully enclosed in a shielded housing, and our upcoming integrated 5G model raises shielding performance to a significantly higher level.

For users assembling the bare PCB without an enclosure, performance will largely depend on how clean the surrounding environment is—both electrically and electromagnetically. A cluttered or noisy shack with many switching supplies or nearby digital devices may severely affect reception quality.

We are often asked why our bare PCBs do not carry a CE mark. The reason is regulatory: under the CE RED (Radio Equipment Directive), the entire assembled device — including shielding, enclosure, antenna, and power supply — is considered the unit subject to compliance testing. Since we cannot control how the PCB is ultimately installed or used, we cannot guarantee compliance with CE-RED standards when the board is used standalone. Fully enclosed versions of our products are engineered to meet those regulatory requirements.
against typical sources of man-made noise.

The transceiver version is fully enclosed in a shielded housing, and our upcoming integrated 5G model raises shielding performance to a significantly higher level.

For users assembling the bare PCB without an enclosure, performance will largely depend on how clean the surrounding environment is—both electrically and electromagnetically. A cluttered or noisy shack with many switching supplies or nearby digital devices may severely affect reception quality.

Power Supply-Related Causes

Power Filtering Differences Between Pi 3 and Pi 4/5

The Raspberry Pi 3 has notably less effective power bus filtering compared to the newer Pi 4 and Pi 5 models. This makes it more prone to introducing or propagating noise in RF-sensitive applications like hotspots.

  • The Pi 3 uses simpler onboard voltage regulation with fewer local decoupling capacitors, especially around the USB and GPIO areas. Ripple from the 5V and 3.3V rails can couple into connected devices.
  • Pi Zero2W, Pi 4 and Pi 5 feature improved power management ICs with better rail isolation, more advanced EMI suppression, and higher-quality onboard decoupling.

This means that when using a Pi 3 with a noise-sensitive device (such as a VHF hotspot board), the onboard regulator and PCB layout may allow more conducted or radiated noise to reach the RF circuitry. This effect is less pronounced on Pi 4 and Pi 5, which are better suited for noisy environments.

Mitigation Tips for Pi 3 Users:

  • Use a low-noise, well-filtered power supply.
  • Add external LC filters or ferrite beads on the 5V input line.
  • Introduce an LC tank if above is not sufficient 

Even when using an official Raspberry Pi power supply, noise may still be introduced into the system:

  • Parasitic Resonance from Switching Supplies
    Most wall-wart PSUs are switching mode (SMPS). Their switching transients can modulate sensitive analog audio paths or RF circuits, causing hum, buzzing, or wideband noise.
  • Insufficient Filtering
    Some power supplies have minimal LC filtering. If the noise is not adequately suppressed, it can enter through the DC line and appear in the baseband or RF path.
  • Leakage from AC to DC
    Cheap or poorly isolated supplies may leak AC ripple onto the DC output, causing low-frequency modulation or ground potential shifts.
  • Ground Loops and Reference Drift
    Ground loops occur when multiple grounding paths exist between components. This can introduce differential voltages or stray currents that modulate the signal path.

Test Tip: Run the system on a fully isolated battery (such as a USB power bank), and ideally do so outdoors. This eliminates parasitic coupling from nearby structures and wiring, helping to isolate whether the power supply or environment is the source of the noise.

Why the 2-Meter Version Is More Susceptible to Noise

A common question is why the 2-meter (144 MHz) version of the hotspot tends to suffer more from noise issues than the 70 cm (433 MHz) version. Several technical reasons explain this behavior:

  • Lower Frequencies Attract More Man-Made Noise
    Man-made noise sources such as switching power supplies, chargers, and computers emit interference that is typically stronger below 200 MHz. The 2 m band falls squarely within this range, while much of this noise rolls off before reaching UHF.
  • Longer Wavelengths Couple More Easily
    At 2 m, many cables, wires, and device traces become efficient antennas for noise pickup because they are closer to a resonant length (e.g., 0.5 λ for a 1 m cable). This makes EMI coupling more effective than at 70 cm.
  • Near-Field Noise Coupling
    Indoor environments often have strong near-field electromagnetic activity. Since 2 m antennas are larger and operate closer to this noise field, they couple more energy than smaller 70 cm antennas.
  • Common-Mode Resonance Effects
    The longer conductors and lower frequencies make it easier for parasitic resonances to form on cables or PCB traces, leading to noise ingress via common-mode currents.
  • Frontend Filtering and Rejection Differences
    2 m receiver sections in some modules may use wider input bandwidths or less aggressive filtering compared to 70 cm, making them more vulnerable to out-of-band EMI.

In short, VHF hotspots are more exposed to environmental and conducted noise simply due to physics and the nature of the band.

Common-Mode Noise Pickup

Noise can enter through more than just the power supply. Cables, antennas, and poor shielding also play a role:

  • Antenna or Coax as a Pickup for EMI
    Small antennas can pick up wideband EMI or power-line harmonics from nearby sources. For setups using coax and a remote antenna, the shield can act as a conduit for common-mode noise if no choke or balun is used.
  • No Ferrites on External Cables
    Power, USB, HDMI, and Ethernet cables can all carry noise into the system. Without ferrites, these cables serve as common-mode antennas.
  • Missing or Ineffective Shielding
    If the hotspot is installed on a bare Raspberry Pi 3 without a metal or RF-shielded case, it becomes highly vulnerable to radiated EMI. Our hotspot enclosures include an integrated shield that greatly improves immunity.

Tip: Use clip-on ferrites (type 31 recommended) on all cables. Wind the cables through the cores multiple times if possible.

Environmental Coupling and Layout Issues

  • Nearby Switching Devices or Inverters
    Devices such as laptop chargers, solar inverters, LED drivers, and dimmers can emit broadband RF noise. Even when not directly connected, they can radiate interference.
  • Wiring in the Walls or Floors
    Household mains wiring can act as a large antenna for harmonics and switching noise, especially if the hotspot is placed near floors or walls.
  • Undefined RF Return Path
    In coax-fed installations without proper grounding or choking, the return path can pick up ambient RF noise and conduct it into the receiver.

Tip: Move the setup outdoors on battery power. If the noise vanishes, the interference is environmental or power-related.

Diagnostic Flow (Simplified)

  1. Test on battery power
  2. Replace antenna with a dummy load and observe change in noise
  3. Add ferrites to all cables
  4. Use a shielded or metal case around the Pi and hotspot
  5. Try setup in a different location, preferably outdoors


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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.