ResiCalcEngineering Lab

周波数⇔波長 変換ツール

速度係数を考慮した変換

Required Parameters

Hz

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Quick Answer

Wavelength (λ) = Velocity / Frequency. In a vacuum, velocity is the speed of light (c). In a cable or PCB, waves travel slower, requiring a Velocity Factor (VF) between 0.5 and 0.9.

Documentation

周波数 ↔ 波長 計算ツール

電磁波の周波数と波長を相互変換します。アンテナ設計、RF、光学でよく使います。

公式

波長 = c / f

ここで c = 光速（299,792,458 m/s）、f = 周波数（Hz）です。

よく使う目安

  • 2.4 GHz WiFi = 波長 12.5 cm
  • 5 GHz WiFi = 波長 6.0 cm
  • 900 MHz 携帯電話 = 波長 33.3 cm
  • FM ラジオ（100 MHz） = 波長 3.0 m
  • 可視光（600 THz） = 波長 500 nm

関連ツール

  • リアクタンス計算ツール
  • トレースインピーダンス計算ツール
  • dBm ↔ W 変換ツール

Design Notes

Never assume signals travel at the speed of light over a PCB or through a coaxial cable. For example, standard FR4 PCB material has a VF of roughly 0.45 to 0.55 depending on the trace geometry. This means a 1 GHz signal, which has a 30 cm wavelength in air, will only have a ~15 cm wavelength on your PCB. If you are designing quarter-wave matching stubs or length-matching high speed lines, using the correct velocity factor is critical.

Common Mistakes

  • 1

    Using c (300,000 km/s) for calculations inside coax cables. RG-58 coax typically has a VF of 0.66, meaning the wave is 34% slower.

  • 2

    Confusing Hz with MHz/GHz resulting in calculation errors off by millions. Always use base SI units or keep track of the scientific notation.

  • 3

    Ignoring the effect of dielectric loading. Exposing a trace to air vs encapsulating it in conformal coating changes the local velocity factor.

Engineering Handbox

1. Convert Frequency: 2.4 GHz = 2,400,000,000 Hz 2. Base Wavelength (Air): λ = c / f = 299,792,458 / 2.4e9 = 12.49 cm 3. Apply Velocity Factor: 12.49 cm × 0.66 = 8.24 cm

VerificationThe wavelength inside the RG-58 coax is 8.24 cm. A quarter-wave stub should be ~2.06 cm.

Knowledge Base

波長の公式は？

λ = c / f。媒質中では λ = (c × VF) / f。例：2.4GHz自由空間 = 12.5cm。

速度係数とは？

媒質中の伝搬速度と光速の比。FR4 PCB ≈ 0.45〜0.55、RG-58同軸 = 0.66。VF = 1/√εr。

なぜ波長が電子回路で重要？

回路寸法がλ/10に達すると伝送線路効果（反射、定在波、インピーダンス整合）が支配的に。

アンテナ長の計算は？

半波長ダイポール：L = c/(2f)。四分の一波長モノポール：L = c/(4f)。

2.4GHz WiFiの波長は？

自由空間：12.5cm。PCB上（VF≈0.5）：約6.25cm。四分の一波長アンテナ：約3.1cm。

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