Calculadora de Frequência de Aliasing
Identifique frequências de aliasing para garantir a fidelidade do sinal amostrado.
PTFE=2.1, PE=2.3, Air=1.0
Characteristic Impedance
57.6 Ω
Characteristic Impedance vs Outer Conductor Inner Diameter
Formula
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.
Exemplo Resolvido
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
Perguntas Frequentes
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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