Transmission Line Impedance Rechner — Formel
## 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
- 50 ohm: Standard for RF and instrumentation
- 75 ohm: Video and cable TV
- 93 ohm: Early computer networks
The velocity factor is 1/sqrt(Er), which determines signal propagation speed.
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
- 50 ohm: Standard for RF and instrumentation
- 75 ohm: Video and cable TV
- 93 ohm: Early computer networks
The velocity factor is 1/sqrt(Er), which determines signal propagation speed.
Lösungsbeispiel
Coaxial cable with D=7.0 mm, d=1.63 mm, polyethylene dielectric (Er=2.3).
- Diameter ratio: 7.0 / 1.63 = 4.294
- log10(4.294) = 0.633
- Z0 = 138 / sqrt(2.3) x 0.633 = 138 / 1.517 x 0.633 = 57.6 ohms
- Velocity factor: 1 / sqrt(2.3) = 0.659