CABLE TESTER TDR : UNI-T UT685B KIT PROBLEM MEASURING LENGTH ON SHORT CIRCUIT

[DiJeFr]

Hello everyone From France,

I have just purchased a UT685B KIT TDR Cable Tester (Time Domain Reflectometry) for €100 from uni-trend
links
https://meters.uni-trend.com/product/ut685b-kit/

It looks a lot like the FLUKE Microscanner 2 which costs €950.
links
https://fr.flukenetworks.com/datacom-cabling/copper-testing/MicroScanner-Cable-Verifier

It allows you to test ethernet and coaxial cables. It measures the length and where the open or short circuit is located, and a tracker of cable. It is announced for an accuracy of +-0.6m or +-4%. the measurements on the open pairs of ethernet cables are good. However, the measurements on pair in short circuits are erroneous; it gives almost double the real values, measure 38m on real 20meters . What if there was a bad impedance match on its output that creates two bounces and it measures the second.
I would like to know if any of you who have this product have noticed this defect or is it a manufacturing defect in the one I purchased. In which case I invoke the warranty.
Otherwise it seems like a good product to me.
I hesitate with the Noayfa NF-8601S but this product seam to me dangerous because, if you put an POE on the main entry you destroy the entry of the device, and NVP (Nominal Velocity of Propagation) can not be choice, you can only measure cable to calibrate the product, and NVP is hidden.
Thank you for your feedback. And have a good day to all of you from South of France.
DJ