Common HF Noise Sources

Power Line Noise

  • Cause: Faulty insulators, corona discharge, or arcing connections.

  • Appearance on Spectrum Display:

    • Series of harmonics spaced at 60 Hz (or 50 Hz) intervals.

    • Wide spikes or comb patterns.

  • Sound: Buzzing or crackling.

  • Mitigation:

    • Identify offending power poles with a directional antenna.

    • Report to the utility company for repairs.

Switched-mode Power Supplies

  • Cause: Common in chargers, LED drivers, and other devices.

  • Appearance on Spectrum Display:

    • Wideband noise, often with harmonic spikes.

  • Sound: High-pitched whine or rough buzz.

  • Mitigation:

    • Replace noisy power supplies with linear ones.

    • Use ferrite chokes on cables.

  • Notes: From Glenn Elmore N6GN: “Families of powerline frequency spaced spurs and hum/growl in a broadband AM detector is most likely NOT “powerline harmonics” per se.  I find it to be a very useful tool for detecting SMPS related ingress but not simple N*60 Hz.

    What I often see is SMPS with poorly filtered DC (one capacitor after a couple of rectifiers) supply “DC” to run a usually-bipolar SMPS.  Those switched edges are very fast and can generate to HF and beyond.  It isn’t always obvious in a USB BW on, say 20m, that this is what your noise is from, it may not sound that different to you, but often in a wide AM detector, all the individual lines that are themselves pretty mush and spread, add coherently such that residual 60/120 Hz on the SMPS’s sourcing supply becomes obvious.”

LED Lighting

  • Cause: Poorly designed LED drivers.

  • Appearance on Spectrum Display:

    • Narrowband or wideband noise.

    • Harmonics can sometimes be seen.

  • Sound: Squealing or periodic buzzing.

  • Mitigation:

    • Replace bulbs with RF-quiet designs.

    • Use ferrite chokes.

Solar Inverters

  • Cause: Inverters for solar panel systems.

  • Appearance on Spectrum Display:

    • Harmonics or broadband interference.

  • Sound: Buzz or periodic tones.

  • Mitigation:

    • Contact the manufacturer for filtering solutions.

Computers and Peripherals

  • Cause: Internal switching power supplies, data buses.

  • Appearance on Spectrum Display:

    • Broadband noise with harmonic peaks.

  • Sound: High-pitched digital hash.

  • Mitigation:

    • Add shielding.

    • Use ferrite cores on cables.

Cable TV Systems

  • Cause: Poor shielding on cables or connectors.

  • Appearance on Spectrum Display:

    • Strong carriers at specific frequencies (e.g., 50-60 MHz).

  • Sound: Pure tones or carriers.

  • Mitigation:

    • Replace or re-terminate cables with proper shielding.

Other Neighboring Devices

  • Examples: Wi-Fi, baby monitors, wireless security systems.

  • Appearance on Spectrum Display:

    • Discrete carriers or periodic bursts.

  • Sound: Pulsed tones or hash.

  • Mitigation:

    • Negotiate frequency adjustments or use filtering.

Timing Signals from GPSDOs

  • Cause: Timing signals generated by GPS-disciplined oscillators (GPSDOs) leaking into nearby equipment.

  • Appearance on Spectrum Display:

    • Regular, narrowband carriers or harmonics, often at known reference frequencies (e.g., 10 MHz).

  • Sound: Stable tones or periodic bursts.

  • Mitigation:

    • Shield the GPSDO enclosure.

    • Use high-quality coaxial cables and connectors.

    • Apply ferrite chokes to all connecting cables.