FreeLists / si-list / [SI-LIST] Re: Rise time bandwidth relation

[olaney@xxxxxxxx]

>   In the instance of an infinite pole, all pass filter a.k.a coax
cable, I've read that BW ~ .31/Tr (10% to 90%).  Can anyone clarify the
origin of THAT number?
 
Certainly not!  Or was that meant as a trick question?  An all-pass
response such as a lossless coax cable, would have infinite
bandwidth, so the formula above would be meaningless.  Or perhaps you
meant lossy coax with some assumed low-pass response...?
 
OK, disregarding the perfect coax that I can't find in any catalog, yes
-- I mean the kind that has a non-zero risetime.  Cutoff and moding
effects can be ignored, though I'd love to see a formula that includes
it!  The mere fact of a cutoff frequency implies that Tr > 0, so even the
"perfect" case can't get there.
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