Minimizing RF Noise in the Radio Environment

Understanding RF Noise Sources

RF noise arises from radiated and conducted sources. Radiated noise comes from natural or man-made emitters and couples directly into the antenna. Conducted noise travels via cables, grounds, or poor shielding into the receiver path. One type can often transform into the other, complicating suppression.

Examples

• Radiated noise: atmospheric QRN, solar bursts, switch-mode supplies, Ethernet radiation.
• Conducted noise: RF currents flowing on coax shields, control cables, or power leads, often converting to differential noise inside gear.

Managing Radiated and Conducted Noise

Mitigation depends on type:

• Radiated: Increase separation or eliminate source; field strength falls with distance squared.
• Conducted: Insert chokes on cable paths, suppress common-mode conversion at feedpoints.

Addressing Conducted Interference

At the feedpoint, asymmetry converts signals:

• Differential RF can become unwanted common-mode currents.
• Common-mode currents can convert back into received differential noise.

Mitigation:

1. High-quality BALUNs: Use designs with strong CMRR to block conversion.
2. Proper RF grounding: A dedicated RF ground (not just safety ground) lowers susceptibility.

Establishing a Clean RF Ground

• Multiple ground rods bonded and kept separate from mains safety ground.
• Use common-mode chokes to isolate RF ground from utility ground mesh.
• Bond all station gear with short, heavy straps.
• Do not choke ground straps; apply ferrites only on interconnect cables where needed.

Shielding and Choking Techniques

• High-quality coax: Double-shielded or foil braid types reduce ingress.
• Connector shielding: Ensure full 360° shield continuity.
• Line isolators & RF chokes: Place on feedlines and shack cables to kill common-mode currents.
• Supplementary ground rods: Help reduce RF impedance in local mesh.
• Common-mode chokes: Separate clean RF ground from safety ground paths.

Mains Filtering Considerations

• Mains filters: Install RF-rated filters at shack entrance; avoid relying solely on built-in PSU filters.
• Device-level filtering: Apply dedicated filters on SMPS and noisy gear.
• Avoid redundant choking: If mains filters are used, added ferrites are usually unnecessary.

Conclusion

Reducing RF noise requires a holistic approach: proper feedpoint treatment, effective grounding, quality shielding, and mains filtering. Address both radiated and conducted sources to lower your noise floor and improve weak-signal readability.

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