Why I²R Matters

In any electrical system, including ham radio gear, a fundamental principle governs power loss: I²R. This formula, which stands for "current squared times resistance," defines how much energy is lost as heat in resistive components.

Power Loss (Watts) = Current² x Resistance

Even small losses in coax, baluns, connectors, or antenna wires can reduce signal strength. While I²R gives a useful conceptual model, most RF system losses are better measured in dB, not ohms. Still, reducing effective resistance (or its equivalent loss) remains the key to efficiency.

Why I²R Losses Matter

Most radio amateurs focus on output power or SWR, but resistive loss is often invisible on those meters. It's especially insidious in components like ferrites, matching units, and connectors, where loss isn't always obvious but can quietly rob you of performance.

  • With 1 amp of current and just 0.5Ω of resistance, you lose 0.5 watts to heat
  • At 5 amps (QRO levels), that loss becomes 12.5 watts

Lowering resistance by using better materials or construction techniques improves overall efficiency, regardless of your operating power.

Why QRO Gear Performs Better - Even on QRP

QRO-rated equipment is built to handle higher current without saturation, heating, or arcing. That means:

  • Lower resistance paths thanks to thick conductors and low-loss cores
  • Better thermal design, reducing performance drift
  • More stable impedance, reducing mismatch losses

When used at QRP levels, this gear operates far below its stress limits, resulting in ultra-low losses and rock-solid performance.

Real-World Examples

  • A QRO balun may have an insertion loss of just 0.1 dB, while lower-quality baluns can exceed 0.5 dB—a significant difference when every fraction counts
  • Ferrite chokes wound on large cores with multiple turns provide cleaner reception and better common-mode rejection
  • Heavy coax with solid shielding and low-loss dielectric means more of your signal reaches the antenna (and comes back)

Conclusion

Optimizing for I²R loss isn't just for high-power operators. Even QRP setups benefit from using high-quality, low-resistance components. QRO-grade gear simply brings lower loss, better stability, and long-term reliability.

Efficiency starts with resistance and I²R tells the story.

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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.