[TowerTalk] Formula

[Richard Karlquist]

>     Where is the reference database and formulae available to 
> calculate the
> lead inductance of copper strapping given the width and depth in 
> inches and
> the length of the copper strap in feet?
> -- 
> Rutherford Resources
> Stephen Rutherford

It depends on how close it is to ground.  You have to estimate
the characteristic impedance of the strap as if it were a
microstrip-type transmission line, ignoring any dielectric
material.  Then the inductance per foot in nanoHenrys is the
same as the characteristic impedancein ohms.  A strap not
particularly close to any ground plane could easily have an
impedance in the several hundreds of ohms, hence an
inductance of several hundreds of nanaHenrys per foot.  A
standard rule of thumb is 20 nH/inch or 240 nH/foot, which
corresponds to a characteristic impedance of 240 ohms.  This
approximately the impedance of a strap that is spaced 10
times its own width from a ground plane. 

For further reading, see Reference Data for (Radio) Engineers.

Rick N6RK