Author Topic: explain TDR Graph  (Read 516 times)

SchattenGeist

  • Newbie
  • *
  • Posts: 11
explain TDR Graph
« on: April 19, 2018, 02:17:34 PM »
Hello.

I'm a developer working in an industrial company. Or network is handled by an external service provider, so here is not other IT guy around. Because one department has massive problems with the network (the service provider is always saying "everything is good") i had just had fulfill a dream of myself and buyed a pocketethernet.

All the test are Ok (I only found some defective patch cable) but the TDR graph shows some interesting (https://imgur.com/a/JZfKP). I've measured with a ~5 Meter patch cable at the start and a 30cm Patch cable at the end (open). The length discovered by TDR are 30 meter (this seems reasonable). Sadly, i'm not able to read the graph. I only see, there can be something at 15 meter. Can someone please explain the graph?

The documentation said, the optimal measurement is done with a correct terminated cable. How to terminate the cable correctly?

I'm sorry bagging you, but I did not know where to ask, and in which forum to ask...

Thank
SchattenGeist

Jeeves

  • Newbie
  • *
  • Posts: 2
Re: explain TDR Graph
« Reply #1 on: April 27, 2018, 10:43:27 AM »
Frist up from the TDR help in the app see below.

TDR
The TDR-based, single ended length measurement and fault locating tests the physical properties of a cable, with just one end connected to Pockethernet. See how long the cable is and if there are any short circuits, split pairs or bad terminations. Pockethernet also detects if the cable is connected to a switched off computer or switch.

The main status line shows the overall result of the measurement if each pair in the cable is terminated the same way (e.g. all pairs are open or connected)

The details section includes a table where you can check the condition of each wire pair: Open, Short (with itself), Short with another pair, Connected to an Ethernet port or Bad Termination (if none of the former apply). Additionally the distance to the fault is shown. The length cannot be determined if the cable is connected to another Ethernet port, as a properly terminated connection doesn't provide signal reflections that can be measured. Also, switched on Ethernet ports on the other end can provide false results as the other device is actively transmitting signals that interfere with the measurement.

Graphical TDR
This features allows you to measure the imperfections of a cable along its whole length or a section of it. A short electrical pulse is sent down the cable, which is reflected from imperfections (short circuits, split pairs, impedance mismatches, open ends) or absorbed by proper termination (another ethernet port). The cable is measured from its beginning until the distance that is set by the slider. For a distance up to 30 meters / 100 feet, a high-resolution plot is conducted. The maximum distance is 300 meters / 1000 feet.

On the plot graphics, the horizontal axis shows the distance, while the vertical axis shows any reflections of the initial test pulse. The 4 color lines correspond to the 4 wire pairs in the cable according to the TIA settings. Short circuits show up as a negative reflection, open ends as a positive one, while with a proper termination the graph is completely flat.

Small imperfections in the +/- 10 range can be caused by cable extenders or patch panels, which can be conveniently detected by this feature.


From this I would deduce that at the 15m mark from the start that there is a pretty high resistance joint/kinked cable.


SchattenGeist

  • Newbie
  • *
  • Posts: 11
Re: explain TDR Graph
« Reply #2 on: April 27, 2018, 11:50:33 AM »
Thank your for copy & paste the manual.  :(

OK, I've readed something with "humidity" in the cable and other strange problems. I thought there will be just a peak when there is 'just' a kinked cable or a connector in the line.

OK, thank you for clarification.

jboxtel

  • Administrator
  • Full Member
  • *****
  • Posts: 157
Re: explain TDR Graph
« Reply #3 on: May 16, 2018, 10:12:29 AM »
We're working on a more in-depth tutorial series where we'll also get into the details of the TDR graph

Re. the image you've send. That graph would tell you it's a cable of approx 25m. (for proper length measurements, rather rely on the TDR feature though since this does several measurements the graph does just does one)

- A small bump within the +10/-10 range would be a cable that doesn't have any shorts or breaks, and is connected to an Ethernet port.
anything bigger than that would indicate an error.
- A bigger positive bump would indicate an open cable
- A bigger negative bump indicates a short

SchattenGeist

  • Newbie
  • *
  • Posts: 11
Re: explain TDR Graph
« Reply #4 on: May 16, 2018, 05:51:19 PM »
Hello.

a tutorial would be great! Could not wait for that :)

On link level the cable is OK - correct terminated, etc. The length measured by TDR (with terminated end) is ca. 30 meter. The BER test shows 0 errors. What do you mean with "open cable"? Is the cable at 15 meter so stretched, that the signal was reflected?


NiallCon

  • Newbie
  • *
  • Posts: 4
Re: explain TDR Graph
« Reply #5 on: June 29, 2018, 03:27:56 PM »
+1 for more indepth tutorial especially in the TDR and interpreting what the graphs mean. Maybe show some examples of what the different graphs mean.

I have 2 examples from 2 spare cables I have lying around.

This is a one metre cable connected to the pockethernet with an open end.
https://drive.google.com/open?id=1B_Ny58EBUAQCIJfVKaooMfz-aa8NvuSH



This is a 4 metre cable connected to the pockethernet with an open end.
https://drive.google.com/open?id=1vIknIoOaACULr9fRvT4YsbQoU9Ry2zuB

They both look quite different and I don't know if one looks better than the other. Hence the need for a tutorial.
Most of the other features in the pockethernet are self explanatory but the TDR and Graphs need explaining.

If you need any help with proof reading....I am very happy to help.

Kind Regards,
Niall

SchattenGeist

  • Newbie
  • *
  • Posts: 11
Re: explain TDR Graph
« Reply #6 on: June 29, 2018, 06:20:42 PM »
The second measurement is a good terminated cable (no open end!). See the y axis: 8 ist below 10.

The first cable is too short for a 'nice' graph. See at the Y axis: near 100 -> open at one Meter