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Author Topic: My strange Hlog finally EXPLAINED  (Read 7443 times)

konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #30 on: April 26, 2016, 10:45:37 PM »

I also attach raw data.
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burakkucat

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Re: My strange Hlog finally EXPLAINED
« Reply #31 on: April 27, 2016, 12:23:20 AM »

As I know this circuit has three bridge taps.

Well that is interesting but in my above analysis and calculation I saw no obvious sign of more than one tap. It just goes to show that we must consider all information about a circuit. If, for example, I saw that Hlog plot the first thing I would probably do is to make TDR measurements from both ends of the circuit. Look at the attached PDF document. In the example trace, the length of the tap is given by the difference between the minimum and the maximum whilst the location of the tap is given by the point where the plot starts to drop down to the minimum.

Quote
What do you say about difference between my usual hlog and hlog with target SNR margin 15 dB (and higher power output)? Do you see that better graph (hlog15db) has also higher attenuation at some frequiences? It implicates there are also measurements errors causing lowering attenuation value.

Please be aware that the transfer function is a negative value, so that when we examine a Hlog plot the zero point of the Y-axis is at the top. Thus greater attenuation is indicated by the curve being further down the Y-axis scale. Greater attenuation is lower down; lesser attenuation is higher up.

You have shown me similar plots before. I really do not know why your circuit behaves that way. It would be nice if you could plot the normal in red and the abnormal in green on the same graph. That would make it so much easier to compare them both.

I also attach raw data.

I have downloaded the data for both Hlog plots. At the moment I'm not sure what I can do with them.

As I have spent hours performing the calculations and then typing up what I had found, earlier this evening, I just do not have any more time to spare.

There are other things in my life that require my time . . . so I am stopping looking at your other Hlog plots.

[Edited to correct a minor error in the description of the JDSU TDR plot example.]
« Last Edit: April 27, 2016, 05:58:46 PM by burakkucat »
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #32 on: April 27, 2016, 12:29:16 AM »

Quote from: burakkucat
It would be nice if you could plot the normal in red and the abnormal in green on the same graph. That would make it so much easier to compare them both.
It would be nice if the script could plot two graphs in this way.
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kitz

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Re: My strange Hlog finally EXPLAINED
« Reply #33 on: April 27, 2016, 03:06:36 PM »

konrado

Please take note that b*cat has other things on right now and has already spent an enormous amount of time trying to help answer your questions.
I'm only butting in  because I know that sometimes you may not notice when people are under pressure and you can miss a hint when someone is trying to be polite.

If he can help, then he will, but just right now he needs to take a breather to do some other things in real life.
Thank you for understanding. :) 
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #34 on: April 27, 2016, 03:20:12 PM »

kitz: now I try to proof my theory. I want to convince burakkucat.
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roseway

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Re: My strange Hlog finally EXPLAINED
« Reply #35 on: April 27, 2016, 03:47:02 PM »

Konrado, please take note of what Kitz said.
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burakkucat

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Re: My strange Hlog finally EXPLAINED
« Reply #36 on: May 03, 2016, 12:19:04 AM »

I have taken another quick look at this and I think I realise what I have been missing. I believe that you have concluded that the equipment is not reporting values in a linear fashion across the entire range. When there is a change in output power there is not an equal change in the representation of the transfer function, visualised by an Hlog plot.

As for the last two data sets that you have provided (usualhlog.txt and hlog15db.txt), I have not plotted them on one graph in different colours (I don't know how to do so without spending time reading the gnuplot documentation) but have, instead, just plotted the delta of the two data sets. (Attached below.)

By considering the two basic Hlog plots (also attached below), we must ignore the two outer limits -- where the sub-carriers (tones) are less than & equal to 30 and also those that are greater than & equal to 400. In other words, we just look at --

400 > sub-carrier > 30

I have not attempted to explain the result. However we can see that the delta is inversely proportional to the sub-carrier (i.e. frequency) and the rate of decay (with frequency) appears to follow an exponential curve. As the frequency rises, fine structure becomes apparent in the actual curve of the delta.
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #37 on: May 03, 2016, 02:40:25 AM »

Quote from: burakkucat
I have taken another quick look at this and I think I realise what I have been missing. I believe that you have concluded that the equipment is not reporting values in a linear fashion across the entire range. When there is a change in output power there is not an equal change in the representation of the transfer function, visualised by an Hlog plot.
1. I assume that unusual-hlog is more accurate representation of real Hlog than usualhlog.
2. I've noticed that on unsual Hlog there are lower value on some tones but there are also higher value on some tones.
3. I conclude that hlog measurement errors are both: up and down.
Did you notice it?
Similarly, shortening the line causes higher attenuation on some tones.
http://forum.kitz.co.uk/index.php?topic=14668.0
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burakkucat

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Re: My strange Hlog finally EXPLAINED
« Reply #38 on: May 03, 2016, 06:01:16 PM »

Having seen many variations on the overall shape of Hlog plots for the three versions of ADSL (G.992.1, G.992.3 and G.992.5) and for VDSL2 (G.993.2), I would have to say that out of the two examples (usual-hlog and unusual-hlog) the one I have labelled unusual-hlog appears to better fit the expected shape.

By looking at the delta plot, we can see that there is most definitely measurement errors in both directions of data transfer. As the input to the plotting utility, the usual- data was the first and the unusual- data was the second. Hence when the value of the unusual- is larger (more negative) that the usual- then the delta will be positive and when the value of the unusual- is smaller (more positive) than the usual- then the delta will be negative. Examining the delta plot allows us to clearly see the differences without needing to state which data set should be accepted as a correct representation.

My statements, above, align with the three conclusions that you have made.  :)

As for your other observation that there is higher attenuation on some tones (sub-carriers) after the physical line length was shortened is somewhat more difficult to rationalise. However I offer the suggestion that the length by which the line was shortened was a very small percentage of the overall line length, hence any such comparative measurements would be of the order of the overall experimental error. The real test must surely be a comparison of the overall (the sigma, the sum of all sub-carriers) attenuation of the line at its original length with that overall attenuation when it had been shortened by a small percentage of its length.  :-\
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #39 on: May 03, 2016, 06:46:37 PM »

I'm glad we came to agreement regarding to these two Hlogs. I'm still not sure if I explained clearly enough that all undulations on my Hlog are caused by measurement errors. I send again other circuit Hlog. Do you see the same pattern at tones 50-100 on very low errors hlog.png? On the remaining tones my errors are not noticable on low errors hlog because there is most disturbing factor on tones 50-100(PSD mask or something similar). Do you still believe that my circuit consists of different gauges?
EDIT: I now see on low errors hlog slightly steeper slope on tones 100-200. It reflects my roll on these tones.
« Last Edit: May 03, 2016, 06:58:29 PM by konrado5 »
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