周波数⇔波長 変換ツール
速度係数を考慮した変換
Required Parameters
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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.
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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
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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