video cable impedance

[Mark7]

<font color='#000000'>Is there are coralation between the capacitance in a video cable and it's charateristic impedance(75ohms). In other words, does a video cable have to be in the range of 16-21 pF/ft of capacitance in order to maintain an impendence of 75 ohms?</font>

 

[gene]

<font color='#000000'>Barring any dissipative effects such as dielectric &quot;leakage&quot; and conductor resistance, the characteristic impedance of a transmission line is equal to the square root of the ratio of the line's inductance per unit length divided by the line's capacitance per unit length:

Z = sqrt(L/C)

You may wish to read an article we did on video cables:

Component Video Cables - Definitive Guide</font>

 

[Mark7]

<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>

gene : <font color='#000000'>Barring any dissipative effects such as dielectric &quot;leakage&quot; and conductor resistance, the characteristic impedance of a transmission line is equal to the square root of the ratio of the line's inductance per unit length divided by the line's capacitance per unit length:

Z = sqrt(L/C)

You may wish to read an article we did on video cables:

Component Video Cables - Definitive Guide</font>

<font color='#000000'>What if you have part of the equation? For example: 90=sqrt(.22/c) &nbsp;where &nbsp;90= impedence .22 = inductance c=capacitance &nbsp;How do you find the capacitance? My algebra is extremely rusty.</font>

 

[Wabbit_Swayer]

<font color='#000000'>a=b*c
b=a/c</font>