[SI-LIST] Agilent TDR Normalization Questions
- From: "Chris Padilla (cpad)" <cpad@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 29 Jun 2005 14:02:49 -0700
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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