Ideally characteristic impedance is independent of frequency. In reality,
it may vary some with frequency, but I don't think the variation is
substantial. The attenuation can vary substantially with frequency. I keep
thinking back to Smith charts. Also, I did some stuff with Hyperlynx
recently. It's pretty neat. It looks at traces on a board layout and
models them as transmission lines. It then shows a series string of
transmission lines representing the trace(s) and lets you look at pulse
waveforms at various points on the trace.

Harold




> Is there an implied frequency when discussing characteristic impedance.
> When we need to analyze cables with respect to their RF
> characteristics we end up with a large table S parameters that have
> been recorded over a range of frequencies.
>
> So when a cable is quoted at 75 ohms, that must be for a given
> frequency.  If so what is it.
>
> Justin
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