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#88: Cheap and simple TDR using an oscilloscope and 74AC14 Schmitt Trigger Inverter

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Published on Apr 21, 2013

This video is a follow on from my previous video that discussed how to measure the length and impedance of coax using an oscilloscope and an pulse generator. This previous video goes into more of the theory and the different measurements you can make. It can be found here:
http://youtu.be/Il_eju4D_TM
However, this video showed the use of a pulse or function generator as the signal source. The problem is that most inexpensive generators won't have a fast enough risetime to be able to resolve shorter cables or finer precision in the measured length. This video shows a very inexpensive circuit that you can build that has a very fast rising/falling edge speed, making it easy to more precisely measure the cables.

It is based on a 74AC14 Schmitt Trigger Inverter chip and a handful of passive components. One of the six inverters is used as an oscillator which drives the remaining 5 inverters in parallel to drive the coax under test.

More detail regarding the Schmitt Trigger circuit can be found in the video uploaded immediately prior to this video:
http://youtu.be/NuXitMK3HSA

This video is shot in HD

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