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Chameleon Knowledge Base · The Complete Online HF Antenna Handbook

Why Does My SWR Change When I Move the Feed Line?

Learn why moving a coaxial feed line can change SWR and what it reveals about common-mode current and antenna balance.

Getting Started HF Fundamentals Reviewed 2026-07-14
Short Answer: Learn why moving a coaxial feed line can change SWR and what it reveals about common-mode current and antenna balance.

Explanation

Overview If moving your coaxial cable changes the SWR, the feed line is likely becoming part of the antenna system. This usually indicates the presence of common-mode current or an imbalance in the antenna installation. Why It Happens Ideally, RF current should remain within the intended antenna system. When RF begins flowing on the outside of the coaxial cable, moving the cable changes the antenna's effective electrical characteristics. Common Causes Common-mode current. Missing RF choke. Insufficient counterpoise. Poor antenna balance. Improper feed-line routing. Possible Solutions Install an RF choke near the feed point. Improve the counterpoise or radial system. Reroute the feed line. Move the feed line away from conductive objects. Applied to Chameleon Products Many Chameleon antenna installations benefit from a properly placed RF choke, particularly portable deployments where feed-line routing varies from one location to another. Related Articles What Is Common-Mode Current? What Is an RF Choke? What Is a Counterpoise? How Should I Route My Feed Line? Related Products CHA MPAS 2.0 CHA LEFS Series CHA TDL CHA BV

The exact result depends on the complete station: frequency, geometry, feed line, matching network, return-current path, environment, operating power, and the reference plane of any measurement. A low SWR establishes an impedance relationship at that point; it does not by itself prove efficiency, radiation pattern, compatibility, or safety.

What to Verify

  • Use the newest official product guide or primary service documentation.
  • Confirm the exact model, revision, components, configuration, and operating conditions.
  • Begin tests at low power and change one variable at a time.
  • Do not infer compatibility from connector or thread fit.

Learn Next

  • Antenna Selection: A Mission-First Decision Guide
  • Engineering Design Tradeoffs in Portable HF Antennas
  • Antenna Measurement Reference Planes
  • Understanding Common-Mode Current

Source note: Independently synthesized with reference to The ARRL Handbook for Radio Communications, 99th edition (2022), and The ARRL Antenna Book for Radio Communications, 24th edition (2019). Verify changing regulations, services, software, specifications, availability, and safety requirements against current primary sources.