Kurt Speaks Out — Updated Technical Notes and Modern Errata

Updated October 2025 — based on the Palomar Engineers Digital Edition (August 6 2017, 140 pages)

The source edition discussed here is freely available from Palomar Engineers: Download the Palomar Engineers Digital E-Book Edition of “Kurt Speaks Out”.

Kurt Speaks Out remains a lively and opinionated classic, yet several technical statements no longer hold under modern measurement. The following corrections consolidate the book’s best ideas with up-to-date RF practice. Each topic has been rewritten as smooth narrative guidance rather than point-by-point rebuttal, while keeping Kurt’s original spirit of cutting through marketing folklore.

Transmission Line Length and SWR

The early claim that “you can’t change SWR by changing transmission-line length” is true only for one continuous, uniform line section. In practical stations, however, we often use multiple line types—say, a long 450 Ω ladder line feeding a short 50 Ω coax jumper. In that situation, changing the length of the ladder line alters the impedance transformation, and therefore changes what the tuner sees. Every transmission line is an impedance transformer: a half-wavelength section repeats the load, while a quarter-wavelength section inverts impedances. Use that property deliberately to present an impedance your tuner or balun can handle. For ladder-line doublets, avoid total lengths near odd quarter-wavelengths of your operating bands; those lengths cause extreme voltage or current at the tuner.

Coax, Skin Effect, and Common-Mode Currents

While Kurt correctly explains that differential currents are confined to the inside of the shield, the statement that “there is no capacitive coupling between inside and outside” is misleading. The outer braid can be excited by near-field imbalance, poor grounding, or asymmetry at the feedpoint. In other words, the outer surface becomes part of a secondary antenna system. Similarly, saying that “SWR does not cause currents on the outside” misses an important nuance: SWR itself doesn’t create stray return currents on the outside of the braid of the coax, but the mismatches that produce SWR often correlate with conditions that do. Treat these as related but distinct effects—SWR describes behavior inside the line, while common-mode (or external return) currents flow on the outside and radiate or pick up noise. The cure is always the same: place a 1:1 current balun at the feedpoint and, if needed, another near the shack.

Feedline Impedance and Transformation

The discussion of 450 Ω line not truly being 450 Ω is entirely valid. In real installations, environment and load determine its effective impedance. The key takeaway is that SWR along a single line is constant, but the impedance seen by the next device—typically the tuner—depends on line type and length. Thinking in terms of impedance transformation rather than SWR “fixing” makes matching decisions more predictable.

Modern Practice for the G5RV and Ladder-Line Doublets

The book recommends a 4:1 balun at the ladder-to-coax transition. Modern practice prefers a 1:1 current balun of high choking impedance instead. Then use a short 3–5 m coax jumper to a tuner. A 4:1 balun can face dangerously high voltages or currents on certain bands, while also trying to maintain balance—a dual task that overheats cores and degrades symmetry. Separate those roles: the current balun enforces balance, the tuner or a dedicated UNUN performs impedance transformation. If a 4:1 UNUN is added on the coax side, a current balun is always needed in front of it.

Quarter-Wave Coax Myths and Minimum Feedline Lengths

Some versions of the book propose adding a quarter-wave coax section after a choke to improve balance. In reality, this trick is narrow-band and sensitive to coiling and velocity factor. A good wideband choke at the feedpoint does the job far more consistently. However, there is one legitimate geometric rule of thumb: when working with multiband antennas that exhibit very different feedpoint impedances across HF, using a minimum total feedline length of roughly a quarter-wavelength of your lowest operating frequency helps keep impedance excursions smoother at the tuner. This does not “tune out” mismatch; it simply ensures that the transformed impedance remains within a range your tuner can handle, even as the load varies across bands. It’s a stability measure, not a magic balancing trick.

Baluns and Their Proper Roles

Kurt’s description of baluns remains largely valid but benefits from clearer function separation. A balun’s first responsibility is current balance—making sure the two legs of the antenna carry equal and opposite currents. Impedance transformation is a completely different job. Combining both in one device (for example, a 4:1 current balun) often leads to overheating or leakage. Use a 1:1 current balun for balance, and add a separate UNUN or let the tuner perform the impedance work.

Why 1:1 Usually Wins Over 4:1

The table showing “better SWR” with a 4:1 balun represents only one specific line length. On other lengths or bands, the opposite may occur. Because a doublet’s impedance can swing from tens to thousands of ohms, a 4:1 ratio can create destructive current or voltage extremes. A robust 1:1 current balun keeps the system symmetrical and lets the tuner safely manage transformation. In nearly all multiband cases, that combination offers the most stable and durable solution.

Resonance, Non-Resonance, and Common-Mode Behavior

Resonance merely affects matching convenience; efficiency depends on current distribution and loss, not whether the system is “tuned.” What matters most in both transmit and receive scenarios is common-mode behavior. On transmit, stray return currents on the outer braid increase RF in the shack; when receiving, they act as noise antennas. The fix is the same in both cases: a strong 1:1 current balun at the feedpoint and, if needed, an additional choke at the entry point. Balanced currents mean quieter reception and a cleaner radiation pattern.

Summary of Practical Fixes

Two architectures summarize the modern approach. For ladder-line doublets: choose a line length that avoids odd quarter-waves, mount a 1:1 current balun at the entry, then feed a balanced tuner through a short coax. For coax-fed dipoles or verticals: place a choke directly at the feedpoint and optionally another at the shack. Keep current balance and impedance transformation separate for maximum reliability and lowest noise.

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