# 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.