[SI-LIST] Re: Agilent TDR Normalization Questions
- From: steve weir <weirsi@xxxxxxxxxx>
- To: cpad@xxxxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 29 Jun 2005 14:38:07 -0700
Chris, the risetime degradation with the cal seems like pilot error to
me. Do you by any chance accidentally have an unwanted memory setting in
effect?
Calibration with cables, typically requires some test structure boards for
that purpose. I would think with all the work that Cisco does, that there
must be some such boards around if you find the right person.
Steve.
At 02:02 PM 6/29/2005 -0700, Chris Padilla (cpad) wrote:
>I've read the Help files included with my 86100B w/ 54754A TDR module
>and I follow what happens when one Normalizes to the end of cable and/or
>test fixture so I understand that. There is an IFT and FIR filters
>being used and then FFT'ing back.
>
>I did a little check, however, and have some seemingly strange results
>that I hope someone here can explain.
>
>I find that as long as I am using decent high-quality cables, the
>Normalization routine will degrade (increase) the ristime of the step
>from ~30 ps (unnormalized step) to ~65 ps: a factor of ~2+. I tried
>this for several different cable I had laying around and they are all
>about the same as far as Normalization goes. Expectedly, the normalized
>step is cleaned up of some higher-frequency content wiggles at the top
>of the step.
>
>Next, I decided to Normalize to the end of the TDR module or put another
>way, I didn't add any cable or test fixtures to the TDR module...I just
>screwed my Cal Standards right to the 3.5 mm SMA on the TDR module.
>Guess what? I got the same ~2x increase of risetime as if I had some
>cable and/or test fixtures attached!
>
>Anyone have an explanation for this? Seems to me that as long as I use
>those "decent high-quality cables", all the Normalization adjustments
>happen INSIDE the TDR module!? What am I missing here...this doesn't
>seem right.
>
>
>My next questions regards even using Normalization in the first place.
>I often see a lot of TDR plots (with TDA Systems logo on them! ;o) )
>that don't appear to have been normalized. It is probably for good
>reason since Normalization appears to chop the bandwidth of the scope
>right in half. I have been learning to use I-Connect and I'm confused
>whether or not I should be using the Normalization routine on my scope.
>
>
>Thanks,
>
>Chris Padilla
>Cisco Systems
>San Jose, CA
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