link Back to the Main 33622A Review http://www.element14.com/community/roadTestReviews/1744
So what is TDR...
Summary From Wikipedia:Time-domain reflectometry - Wikipedia, the free encyclopedia
Time-domain reflectometry or TDR is a measurement technique used to determine the characteristics of electrical lines by observing reflected waveforms It provides a powerful means of analysing electrical media such as coaxial and Twisted pair cable and enabling the detection of faults in the wire
The impedance of the discontinuity can be determined from the amplitude of the reflected signal . The distance to the reflecting impedance can also be determined from the time that a pulse takes to return. The limitation of this method is the minimum system rise time. The total rise time consists of the combined rise time of the driving pulse and that of the oscilloscope that monitors the reflections.
Method:
The TDR analysis begins with the propagation of a step or impulse of energy into a system and the subsequent observation of the energy reflected by the system. By analyzing the magnitude, duration and shape of the reflected waveform, the nature of the impedance variation in the transmission system can be determined.
For a Resistive load
If a pure resistive load is placed on the output of the reflectometer and a step signal is applied, a step signal is observed on the CRT, and its height is a function of the resistance. The magnitude of the step produced by the resistive load may be expressed as a fraction of the input signal as given by:
where 
is the characteristic impedance of the transmission line.
So, enough of Wikipedia , what does this mean to you and I.
First up.. What is TDR
How long is a piece of Wire and what is the speed of light anyway?
Setup images
Initial measurement of RG58 Coax and then the Math's
this is the RG58 scope trace, period between pulse and reflection is 64.8nS which with a velocity factor of 66% equates to 21.03 feet. When I measured the cable with a tape it measured 20.79 feet, allowing for about 3inches of "T" connector, that's a pretty accurate measurement
Sorry I have not added cursors to my scope software yet
Oh no, Ohms law seems to be broken...
Measuring and then calculating the length of RG6 Coax using TDR with the 33622A AWG
this is the RG6 scope trace,(Scope settings are the same as before) period between pulse and reflection is 61.8nS which with a velocity factor of 81% equates to 24.61 feet. When I measured the cable with a tape it measured 24.93feet, allowing for about 3 inches of "T" connector, that's a pretty accurate measurement
Measuring and Calculating the length of UTP cable
Screen Capture for UTP Cable, only difference is the timing is now 50nS
Period between pulse and reflection is 480nS which with a velocity factor of 73% equates to 172.3 feet. When I measured the cable with a tape it measured 174.5feet, that's a pretty accurate measurement
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