Hi Scott

TDR (Time Domain Reflectometer) is a device which give you information about
the impedance along the line. It based on the reflected (Echoed back)
signals of a step function. Shorter rise time, of the step, allows higher
definition of lenghf (like thiny scratches) and reach in harmonics up to
several gigahertz. The frequency range of the TDR is always between the
repetition frequency of the step and the highest usefull harmonic frequency.
There is no meaning for a range of 50-100 Mhz.

The best TDR should go up to several gigahertz. If you will select TDR with
slow rise time, you will use a lot of resolution which is important for the
test. Slow rise time TDR is used for testing 
telephone lines where the resolution is not as important as in PCB.

Avner Drory

At 12:19 PM 09/09/96 -0700, you wrote:
>From: Scott Westheimer
>Date: 9/9/96
>
>We have a customer that has an HP TDR machine and is currently measuring at
>2 Ghrtz. They do not know how to change the machine to measure at lower
>readings, i.e. 50-100 Mhrtz. Could someone please explain how they could do
>this.
>
>Thank You
>
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