Calculateur de Fréquence de Repliement
Calculez la fréquence de repliement (aliasing) dans un système numérique.
PTFE=2.1, PE=2.3, Air=1.0
Characteristic Impedance
57.6 Ω
Characteristic Impedance vs Outer Conductor Inner Diameter
Formule
Coaxial Cable Characteristic Impedance
The characteristic impedance of a coaxial transmission line depends on the ratio of conductor diameters and the dielectric material.
Formula
Z_0 = (138 / sqrt(Er)) x log10(D / d)
Where D is the outer conductor inner diameter, d is the inner conductor outer diameter, and Er is the relative dielectric constant.
Common Values
The velocity factor is 1/sqrt(Er), which determines signal propagation speed.
Exemple Résolu
Coaxial cable with D=7.0 mm, d=1.63 mm, polyethylene dielectric (Er=2.3).
- 01Diameter ratio: 7.0 / 1.63 = 4.294
- 02log10(4.294) = 0.633
- 03Z0 = 138 / sqrt(2.3) x 0.633 = 138 / 1.517 x 0.633 = 57.6 ohms
- 04Velocity factor: 1 / sqrt(2.3) = 0.659
Questions Fréquentes
Why are 50 and 75 ohms standard?
50 ohms balances power handling and attenuation. 75 ohms minimizes attenuation and matches the impedance of dipole antennas.
How does dielectric constant affect impedance?
Higher dielectric constant lowers impedance for the same physical dimensions. It also reduces velocity factor, making the cable electrically longer.
Can I use this for other transmission line types?
This formula is for coaxial lines. Microstrip, stripline, and waveguide have different impedance formulas based on their geometry.
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