question about tdr_pci3100

[torr...@eel.upc.es]

Dear Bruce,
Sorry for multiple posting. I failed twice. List account is full. May I send
this message to this address? (Sorry for this silly question).
Thank you.

Dear listmembers,

We can not understand an item in a (Metallic)TDR PC's card pci-3100, purchased
long time ago that, otherwise, it works fairly well:

For instance, we measure a good RG-58 (50 Ohm impedance) cable ended with a
short circuit. The instrument traces a plot: reflection coefficient versus
time. The coefficient is almost zero until it reaches the end of the cable
(that it is not perfectly sharp due to pulse dispersion).

The phenomenon we do not understand is that reflection coefficient is slightly
increasing along the time until reach the short circuit. If the instrument
sends a pulse we do not have information until the echo arrives. How the
instrument represents a (increasingly) continuous trace over time?

Thank you in advance. Sincerely,
Josep M. Torrents
Technical University of Catalonia.


Off the record: Dear Bruce,
We are planning to write a generic paper in a local magazine (Mundo
Electrónico). May we use this material? May we ask for permissions? Would you
please give us permission to use some of the pictures
from http://www.sowacs.com/sensors/tdr.html?
Thank you again.




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[g...@serv.net]

Energy from the pulse is reflected continuously by imperfections in the
cable indicating impedance variations beginning with pulse initiation.
Your plot actually indicates variations in electrical impedance vs
distance from the generator translated into the time domain by use of a
pulse.

MLG