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Chameleon Knowledge Base · The Complete Online HF Antenna Handbook

What Is the Sunspot Number (SSN)?

Learn what the Sunspot Number (SSN) is and how it relates to HF radio propagation and the solar cycle.

Getting Started HF Fundamentals Reviewed 2026-07-14
Short Answer: Learn what the Sunspot Number (SSN) is and how it relates to HF radio propagation and the solar cycle.

Explanation

Overview The Sunspot Number (SSN) is a measure of the number of visible sunspots and sunspot groups present on the Sun. Because sunspots are associated with increased solar activity, they are closely related to the strength of the Earth's ionosphere. General Guidelines 0–25 – Very quiet Sun. 25–75 – Moderate activity. 75–150 – Strong HF conditions. Above 150 – Excellent high-frequency propagation. Relationship to HF Propagation Higher sunspot numbers generally increase ionospheric ionization, improving propagation on the higher HF bands. Not the Only Indicator Although useful, SSN should always be considered alongside Solar Flux Index, K Index, and current space weather conditions. Applied to Chameleon Products Monitoring SSN helps Chameleon operators anticipate changing band conditions throughout the solar cycle. Related Articles What Is Solar Flux Index? What Is the Solar Cycle? What Is MUF? What Is the F2 Layer? Related Products All Chameleon HF Antennas

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.