Case Study 5: Noise Floor from DC to 60MHz is Higher than ITU Models Predict

Symptom:

• The receiver’s noise floor does not follow the expected ITU noise model.

• Instead of gradually decreasing, it remains elevated across the HF spectrum.

Analysis:

• This suggests broadband noise pollution from multiple sources, possibly from local electronics, solar inverters, or poor grounding.

Mitigation Steps:

1. Determine Internal vs. External Sources:

• Power the station from batteries only to isolate internal noise.

• Use a portable receiver outdoors to compare local vs. environmental noise.

2. Reduce Local Noise:

• Install ferrites on power cords and data cables.

• Use shielded network cables to reduce Ethernet leakage.

• Ensure that LED lights and smart devices aren’t contributing noise.

3. Improve Antenna Placement:

• Move antennas away from structures and noisy equipment.

• Use a loop antenna or a high-pass filter to eliminate low-frequency noise.