[time-nuts] T.I. experimenting - newbie question

[Hal Murray]

> But, does the impedance have any effect on VOP?

Not normally.  It's 1/sqrt(dielectric constant * magnetic permeability)

For most materials used as insulators, the magnetic permeability is 1 so we 
tend to drop that part.

http://en.wikipedia.org/wiki/Coaxial_cable

There are a couple of interesting cases where you don't have a simple 
dielectric constant.

Outer traces on a PCB have air on one side and glass/plastic on the other 
side.  They are slightly faster than inner traces.  That corresponds to a 
lower dielectric constant which is what you would expect if mixed 
glass/plastic with air.  (Most of the energy is between the trace and the 
adjacent plane so the air doesn't contribute much.)

Foam coax is a mix of plastic and air.  That gives a lower dielectric 
constant and lower loss.  (That's lower than solid whatever material you are 
using.)

If you find a chart of coax impedance and pick similar insulation at 50 and 75 ohms, the velocity will be the same.


-- 
These are my opinions, not necessarily my employer's.  I hate spam.