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Electronics & Antennas for Ham Radio

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General Antenna Tuning Advice, where to place the resonance dip?

Related reading:
Why an External Tuner Is a Necessary Tool for Wire Antennas — and a Good Investment
Folding Back vs Cutting Wire Antennas — Essential Tips for Optimal Performance

Achieve reliable matching and stable performance across your desired band with minimal stress on tuners, amplifiers, and antenna components.

Basic Principle

If you have a choice where to place the SWR dip, and your antenna doesn’t perfectly cover the entire band:

Prefer placing the dip slightly below the band center.

  • This results in inductive reactance across the band.
  • Inductive loads are generally easier to match and cause less stress on matching equipment.

When SWR < 2:1 Across the Band

  • It usually doesn’t matter much where the dip is.
  • Most modern tuners (internal or external) will handle this range comfortably.
  • Losses are low, and performance is usually acceptable across the band.
  • You can safely place the dip in the middle or at your most-used frequency.

When SWR > 2:1 Across the Band

  • Dip placement becomes more important.
  • Aim to place the dip just below the operating band to stay in the inductive zone.

Why Inductive Reactance Is Preferred

  • Tuners (especially Pi- or L-networks) often work better with inductive loads.
  • Amplifiers—particularly tube amps—are more stable and tolerant of inductive reactance.
  • Capacitive loads can:
    • Be harder to match
    • Cause instability in the tuner or amp
    • Result in higher voltages across traps, feedpoints, or baluns

Rule of Thumb

If you must choose, always favor inductive reactance within your operating band.
Place the SWR dip slightly below the desired band rather than above it.

Practical Example

Operating on 20 m (14.000 – 14.350 MHz)?

  • SWR dip at 13.900 MHz → inductive across the 20 m band → easier tuning.
  • SWR dip at 14.300 MHz → capacitive below 14.300 MHz → more difficult tuning at the start of the band.

Additional Tips

  • Don’t chase the perfect 1.0 : 1 SWR. Anything below 2 : 1 is usually acceptable.
  • If your antenna has multiple resonances (like an OCF dipole), balance the placement to minimize tuner effort across all bands.
  • Keep notes of where the SWR dips occur and how your tuner behaves — it helps when adjusting or retuning later.

Summary

  • < 2 : 1 SWR → Dip placement is flexible.
  • > 2 : 1 SWR → Prefer inductive loads by tuning slightly below the target band.
  • Inductive = good. Capacitive = potentially troublesome.

This tuning strategy improves tuner compatibility, reduces voltage stress, and increases system efficiency — especially when working with wideband antennas or less-than-ideal feedlines.

Mini-FAQ

  • Does it matter if my SWR is slightly above 2 : 1? — Not much. Modern tuners easily handle up to 3 : 1 on HF.
  • What happens if I tune above the band? — You’ll move into a capacitive zone, which can make the tuner less efficient and more unstable.
  • Can I shift the dip without cutting wire? — Yes, fold back small wire sections instead of trimming — see our related article on folding vs cutting.

Interested in more technical content like this? Subscribe to our updates for deep-dive RF articles and lab notes:
https://shop.rf.guru/pages/subscribe

Questions or experiences to share? Feel free to contact RF.Guru.

Joeri Van Dooren, ON6URE — RF engineer, antenna designer, and founder of RF.Guru, specializing in high-performance HF/VHF antennas and RF components.

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