[SI-LIST] Re: SMA cable for TDR
- From: "Zabinski, Patrick" <zabinski.patrick@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>, "Bill Dempsey" <bdempsey85@xxxxxxxxx>
- Date: Tue, 28 Oct 2008 19:44:36 -0500
To characterize dispersion, group delay with a VNA is optimal.
To see the effects of dispersion, TDR (assuming good/fast edges) is
great. Eye diagrams can also be useful, but it's more difficult to
separate out the effects of dispersion from discontinuities, crosstalk,
...
As for noticing the effects of dispersion, we generally see it most when
using economical (i.e., poor performing) cables. We were once ordering
passive probes from a company that had 18" leads; the coax was
relatively small diameter (roughly 0.200").
> Pat,
> I'd like to learn a bit about the 'noticeable dispersion' in the coax
> cables. I had a chance to measure the really nice Gore
> cables and up to
> 20GHz the VNA I was using showed flat group delay.
>
> What method do you use to measure coax cable dispersion? How
> noticeable was
> it?
>
> Thanks,
> Bill
>
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