> 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. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
