On Fri, Mar 17, 2006 at 10:13:59AM +0000, Dieter wrote:
>
> The difference between a 50 Ohm BNC and a 75 Ohm BNC would be...
> different insulator/dielectric ?
>
Probably not. Coaxial transmission line impedance is proportional
to the log of the ratio of the outer conductor radius to the inner conductor
radius. Real coaxial connectors maintain the appropriate radius ratio all
the way through the mated pair, to achieve the desired impedance.
Dielectric constant applies a fudge factor to the required radius ratio, but
there aren't that many suitable dielectrics. So the practical way to design
a connector is to pick the dielectric for the desired properties, then
calculate the necessary ratio of outer conductor I.D. to inner conductor
O.D. There are various other details to consider, and the further into the
microwave region you go, the pickier they get. But that's the basic
principle.
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