Rune,
I am taking a deeper look at your TDR plot. Thanks for implementing this.
I think you are plotting all of the samples of the IFFT of the S11 data. If so, I would recommend that you chop off the last half of the plot. With 5 segments (505 total samples) from 50kHz to 900 MHz I am seeing the right side of the plot indicating 55.4 m as the longest distance one could measure. I set the the cable type to RG58/U with a velocity factor of 0.66. I think 55.4 m is too large by a factor of 2. The last half of the bins in the IFFT are time delays that we won't measure in this way with real cables. As it is, you give the impression to someone that they could measure a 55.4 m cable for the settings indicated above which is not correct.
Are you applying a frequency domain window function to the data prior to doing the IFFT? If so, it would be useful to let folks know what window you are applying when it comes time for documentation. If not, there are an infinite number of possible windows. I would suggest something fairly easy to implement such as a Hanning window or a Hamming window. For cable length measurement, what you have is great.
I am interested in using the TDR to look for impedance deviations along the transmission line which can get easily obscured by time-domain sidelobes if no window is applied. I am using the TDR capability to look for coax damage or breaks in the protective jacket caused by gardening. My coax cables run through a garden area to my antennas which are above the garden. Outright breaks in the coax are fairly easy to find; however, some types of damage are a bit more difficult to observe. The TDR is especially helpful for this application.
I do like the separate plotting capability you have implemented for the TDR data which is in the same window as the coax definition. I have noticed that once you put it into the main window as one of the graphs, you cannot ever see the TDR data again as a separate plot unless you restart the program. It seems like it would be a good idea to restore the plot to the TDR window if it is removed from the plots in the main window or just permanently leave it in the separate window that the user can bring up as desired?
Another alternative is to only plot the TDR data in the main window. When the TDR plot is a graph in the main window you should show at least the velocity factor you have assumed on the TDR plot and perhaps the cable type the user selected. This makes the plot self-contained when it is saved as an image. I prefer a separate window where I can make the TDR plot as big as my screen; however, that is not in any way essential and probably makes more work for you.
Thanks, again, for your great work on this software. I greatly appreciate it.
73,
Bryan, WA5VAH
