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Ham RFI Starting Point

Presented by Jim Bacher, WB8VSU, at Hamvention 2025. The presenter shared practical insights into tackling High-Frequency Man-Made Radio Interference (HMRI) from a ham radio operator’s perspective. Starting from basic RF principles—like the bidirectional nature of signals and return current paths—the session highlighted how improper shielding and cable routing can lead to unwanted radiation. Emphasis was placed on understanding near-field and far-field behavior, the role of inductance in RF paths, and how even simple construction techniques like probe loops or antenna coax hacks can aid diagnostics. The talk was rooted in real-world observations, including testing results from modern computers, power supplies, and medical-grade equipment. Digging deeper, the presenter addressed regulatory aspects, noting how FCC guidelines often lack clarity compared to stricter European standards. A detailed look at switching power supplies revealed common pitfalls, such as routing wires near switching inductors, which can inject noise back into a system. Real lab plots from FCC test facilities and examples of conducted and radiated emissions gave credibility to the troubleshooting methods shared. Attendees were reminded that using high-quality cables, avoiding no-name electronics, and designing with RF in mind aren’t just best practices—they’re essential. Practical tools like SDRs, homemade RF probes, and trip-lite isobars were recommended as effective, low-cost solutions for identifying and mitigating interference in the shack.