# FRR Measurement in Digital Oscilloscope

#### shahbaznihal

Hello,

This is my first post in this domain and I am fairly novice in this subject, so please bear with me.

I have a GDS-20174A Digital Oscilloscope. I am trying to measure the delay between two BNC cables using a Square Pulse of 2V with an offset of 1 V using the oscilloscope. I am using the FRR measurement to do so. My question is,
1) Does the trigger level of the oscilloscope concerns the FRR measurement?
2) The mean of 1000 samples fluctuated and so does the standard deviation?
3) The rising pulse is not strictly "square", how does your oscilloscope measure the FRR in this case?

Moreover, these measurements depend significantly on the timebase of the oscilloscope. The manual of the oscilloscope is available here.

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#### Baluncore

I am trying to measure the delay between two BNC cables using a Square Pulse of 2V with an offset of 1 V using the oscilloscope. I am using the FRR measurement to do so.
Exactly what is an FRR measurement.

A 200 MHz analogue front end with 1 Gs/s will not enable you to compare cable lengths. 1 GHz has a period of 1 nsec. That is about 300 mm in a cable. The front end will blur the signal further. Your resolution will be very poor, maybe one metre.

To compare the electrical length of two similar open-circuit cables, drive the cable with a sine wave, through a series termination resistor. Use a two channel oscilloscope to observe the phase shift of the signals at both sides of the termination resistor. Adjust the sinewave frequency to minimise phase shift, record the frequency. Repeat the process for the other line.

#### shahbaznihal

Exactly what is an FRR measurement.
The FRR function calculates the time delay in the rising pulse of two signals.

#### berkeman

Mentor
I have a GDS-20174A Digital Oscilloscope. I am trying to measure the delay between two BNC cables using a Square Pulse of 2V with an offset of 1 V using the oscilloscope. I am using the FRR measurement to do so.
What is your signal source? What are the rise and fall times of the pulses? What is the period between pulses?

The FRR measurement doesn't look like it would be used for time delay reflectometry -- looks more like a signal propagation measurement where you have clear access to the signals at different locations. Do you have access to the far end of the cable? (can the cable be looped back to the near end at the oscilloscope?

"FRR Measurement in Digital Oscilloscope"

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