View Single Post
  #3   Report Post  
Posted to
Jeff Liebermann Jeff Liebermann is offline
external usenet poster
Posts: 4,045
Default Coax cable calculation

On Tue, 10 Apr 2018 16:42:43 +1000, Trevor Wilson

Here's a question that stumped me back in the old slide rule days:

A coaxial cable, having an inner diameter of 0.0254mm (0.001") and using
an insulator with a dielectric constant of 2.56, is yo have a
characteristic impedance of 2,000 Ohms. What must be the outer conductor
- Select inches.
- Plug in any number for outside dia (D) trial an error.
- Plug in 0.001 for inner diameter (d).
- Plug in 2.56 for permittivity (er) (same as dielectric constant
in this example).
- Punch "calculate"

I used 1,000,000 inches for outside diameter and still obtained only
776 ohms. 1,000,000,000 inches yielded 1035 ohms. I don't think it's
going to make it to 2,000 ohms unless the coax cable is absurdly huge.

Jeff Liebermann
150 Felker St #D
Santa Cruz CA 95060
Skype: JeffLiebermann AE6KS 831-336-2558