High-Voltage Protection in UNUN and BALUN Design

High-power RF systems don’t just push performance boundaries—they push dielectric boundaries too. That’s why, at RF.Guru, our UNUNs and BALUNs aren’t just tuned for RF efficiency but are built from the ground up to handle extreme dielectric stress. Every design choice—from materials to mechanical fixings—is aimed at one thing: withstanding up to 20 kV of potential without corona, arcing, or creeping discharge.

HV Coating Inside and Out

Every enclosure is fully lined with a high-voltage dielectric coating rated at 10–15 kV/mm, creating a barrier that prevents surface creeping and internal arcing even under QRO stress. This coating is generously applied, especially around high-potential points, to eliminate corona discharge risks—an often-overlooked problem in high-power UNUNs and BALUNs.

3M EPDM Gaskets for Industrial Sealing

On all SO-239 and N-type connector interfaces, we use 3M HV-rated EPDM gaskets—not generic rubber. These gaskets have a breakdown voltage of 20–25 kV/cm, maintain elasticity under compression, and offer excellent water sealing. They also suppress micro-arcing by spacing conductive surfaces beyond the corona threshold.

PTFE Washers and Internal Dielectrics

We use PTFE washers—internally and externally—because of their exceptional dielectric strength: 60–80 kV/mm. These are mounted on both sides of the M6 stainless hardware to isolate conductors from the enclosure, increase creepage distance, and suppress corona in feedthroughs.

Rounded Fasteners: No Sharp Edges, No Corona

Corona loves sharp metal edges. That’s why we use:

  • Rounded M6 stainless bolts with dome heads
  • No sharp-pointed hardware
  • Wide, rounded thumbscrews that avoid overstressing terminals
  • Nylon locking nuts on the outside, eliminating the risk of metal-to-metal arcs in moist environments

We deliberately avoid hex nuts and sharp washers at HV terminals. These are common failure points due to edge-induced corona and user over-tightening. Even our thumbscrews are profiled to reduce electric field gradients that could trigger discharge.

Mechanical Design to Avoid Creeping Paths

  • Spacers lift the entire assembly from conductive surfaces.
  • Internal layout doubles the spacing found in conventional 4:1 UNUNs.
  • Creepage paths are extended using insulating barriers and coating layers.
  • All mechanical penetrations are gasketed or potted.

It’s Not Just Electrical—It’s Expedition-Proven

Our dual-core 1:1 and 1:4 designs have been tested under real 1.5–2 kW multi-station contest load conditions (VU Andaman, MJ/OP2D Jersey DXpedition, among others). These aren’t lab experiments. They’re field-proven under brutal RF and tropical humidity—where corona, leakage, or arcing would show up fast.

Bottom line:
Corona doesn’t announce itself. It starts as an invisible failure and ends as a melted mess. That’s why we use industrial-grade dielectrics, rounded mechanicals, and HV-rated materials throughout—even if most users will never see them.

Built for 20 kV. Ready for the real world.

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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.