# [SI-LIST] Re: Transmission line capacitance

• From: DAVID CUTHBERT <telegrapher9@xxxxxxxxx>
• To: rahul kumar <rahul05kumar@xxxxxxxxx>
• Date: Sat, 24 Oct 2009 09:01:50 -0600

```Two handy transmission line formulas:
C = td/Z
L = td X Z

td is the propagation time
Z is the characteristic impedance

Example: 1 cm of line, Z = 100 ohms, time is 67 ps (effective relative
dielectric constant is 4)

C = 67ps/100 ohms = 670 fF
L = 67ps X 100 ohms = 6.7 nH

Dave Cuthbert

On Sat, Oct 24, 2009 at 3:34 AM, rahul kumar <rahul05kumar@xxxxxxxxx> wrote:

> Hello all,
> I have seen in standards quoting transmission line capacitance equal to
> 1.5pF per cm . How this number is calculated?
> Is this value frequency dependent? transition dependent ?
>
> Kindly help.
>
> Thanks
>
>
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