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[konrado5]

It is curious patent. In the case of HR faults, upstream attenuation increases relative to downstream attenuation. In the case of shunt (damage of insulation around the wires) downstream attenuation increases relative to upstream attenuation.
http://www.google.com/patents/EP2747401A1?cl=en

[burakkucat]

Thank you. That is a very interesting patent. 

I have downloaded a copy (as a PDF file) to carefully read at a later time.

[konrado5]

Is it implicates that my one day attenuation 23.5/20.2 dB instead 25.0/14.8 dB was caused by one day HR fault? In this patent I don't see anything whether downstream attenuation drops at the expense of upstream attenuation or rather upstream attenuation increases without change in downstream attenuation.

Best regards
konrado5

[renluop]

May be completely off beam, but attached are stats before and after an upstream SNR super-wobbly. It has happened before, the up sync being hit whilst downstream has  a minimal increase.

Sorry for butting in, K!

[burakkucat]

Is it implicates that my one day attenuation 23.5/20.2 dB instead 25.0/14.8 dB was caused by one day HR fault?

I'm not sure if you can take what that patent describes, map it to your one-day situation and then suggest that you had a transient, one-day HR fault.

My current understanding of that patent is that for a given xDSL service (be it G.Dmt, ADSL2, ADSL2+ or VDSL2) one can consider that there is a distinctive line attenuation for the DS direction and the US direction which will be perturbed by certain classes of faults. If the attenuation ratio (of DS / US) for a particular circuit is compared with the average of a large number of similar circuits of the same class and the result shows a discrepancy, then either a HR fault (in series with the circuit) or a low insulation fault (shunting across the circuit) can be proposed.

I'll take this opportunity in "flagging up" the above patent for examination by other Kitizens. I regard it as a very interesting and significant find by Konrado5. 

[konrado5]

I'm not sure if you can take what that patent describes, map it to your one-day situation and then suggest that you had a transient, one-day HR fault.

It is also complicated, because admittedly I had higher upstream attenuation one day (20.2 dB instead 14.8 dB) however on almost every frequency my downstream attenuation was lower. Second graph is one day graph. Unfortunately, I have no correct upstream Hlog datas from one day. Perhaps only some upstream frequiences were more attenuated that day.

[JGO]

 If the attenuation ratio (of DS / US) for a particular circuit is compared with the average of a large number of similar circuits of the same class and the result shows a discrepancy, then either a HR fault (in series with the circuit) or a low insulation fault (shunting across the circuit) can be proposed.

I'll take this opportunity in "flagging up" the above patent for examination by other Kitizens. I regard it as a very interesting and significant find by

The object is to throw up deviation from "normal" by comparing with the average of several comparable lines.  This is probably the best someone in the field can do, BUT if the user has been making a record over time for his single case, I think that is a better indicator of deviations from normal for his setup. There is the caution that all readings won't all be in the same weather conditions so there will be an extra slight fluctuation as well as to HR/SC faults. OTOH the problem of ensuring  lines  are comparable is eliminated.

 I don't claim to be an expert statistician so other inputs welcome.
   

[burakkucat]

Just thinking out loud . . .

I assume that the effect on the attenuation ratio is significant for the type of faults that are hoped to be detected but that (say) temperature effects on the attenuation ratio are quite small.

I wonder if it is something that could be incorporated into the Eagle code? Consider a VDSL2 circuit. The medley phase defines the tones in use for DS & US. Use that information to take the relevant information from the Hlog data. Calculate the arithmetic mean to give a value to DS & US attenuation. Perform the division and display the dimensionless value. Hmm . . .

[konrado5]

In JDSU manual I've found on page 2.

Other impairments types can be seen in HLog data. This HLog data plot in Figure 3 shows a large roll-off
or increased attenuation in the lower frequencies that is characteristic of a capacitive issue typically
associated with poor electrical connections with one of the loop leads in a connector at the premises.

http://www.elnex.pl/product/attachment/d096f15ee037f5f693e1f7867366a54a/pl_PL/Analiza-petli-abonenckiej-SmartClass-TPS.pdf
Perhaps one day I had no or slighter capacitive fault than on every other day unless whole upstream band was more attenuated (I had average upstream attenuation significantly higher: 20.2 dB instead 14.8 dB).

[konrado5]

Crucial excerpt of the patent.

0035]
Conversely, if the attenuation ratio of the test line is below the lower threshold, then a second type of fault condition is identified. Specifically, this second type of fault is a high resistance connection, typically referred to as an "HR joint", affecting a join between sections of wiring. It is perhaps more accurate to describe such a condition as an impedance in the metallic path as it is usually not simply resistive and may include capacitive and rectifying junction characteristics. In good joints, the "clean" core metal of each end section of wiring are touching each other, and a twist is usually applied or compression crimp connector fitted to maintain the contact. Figure 7a shows a (stylised) twisted joint between two sections of a single metallic core wire. Ideally, the physical contact is maintained along the length of the joint as illustrated in Figure 7b where the same stylised joint is shown but with no twist applied. This results in a good electrical joint of low impedance. Whilst it is common for such joints to be given a further protective covering treatment, as well as electrical insulation, they are still prone to degradation. Figure 7c shows a joint where the metal core has reacted to form surface chemical compounds that can behave as a dielectric insulator. This might happen over time simply due to oxidation from exposure to the air, or can happen more rapidly if water comes into contact with the joint. Electrically, this type of fault behaves like a series capacitance as illustrated in Figure 7d. In such situations, the attenuation of low frequencies increases relative to higher frequencies, thus disproportionately affecting the upstream path. In other words, upstream attenuation tends to increase relative to the downstream attenuation, resulting in a decrease in the attenuation ratio.

The question remains unanswered whether my one day attenuation 23.5/20.2 dB instead 25.0/14.8 dB was one day mitigation of HR fault or rather one day enhancement of HR fault. The beginning frequiences of downstram was significantly less attenuated than it is usually.

Best regards
konrado5

[burakkucat]

The question remains unanswered whether my one day attenuation 23.5/20.2 dB instead 25.0/14.8 dB was one day mitigation of HR fault or rather one day enhancement of HR fault. The beginning frequiences of downstram was significantly less attenuated than it is usually.

I don't think anyone will be able to answer that question for you. 

Values are usually around: DS 25.0 dB and US 14.8 dB
Giving a ratio of: 1.7 (to one decimal place).

On one day the DS dropped from 25.0 dB to 23.5 dB whilst the US increased from 14.8 dB to 20.2 dB
Giving a ratio of: 1.2 (to one decimal place).

So on that one day the ratio had dropped by 0.5 but we can see that as both the DS and US values had deviated from the normal values it is impossible to say whether a hypothetical joint had become more resistive or more capacitive.

The difference in the DS values is 1.5 dB. The difference in the US values is 5.4 dB. Looking at the two differences, that of the US is the more significant. What can be deduced? I really do not know. 

[konrado5]

Is capacitive joint the same as HR joint ? It is strange that HR fault does not affect on SNR margin stability, my SNR margin is very stable.

The difference in the DS values is 1.5 dB. The difference in the US values is 5.4 dB. Looking at the two differences, that of the US is the more significant. What can be deduced? I really do not know. 

I think it was rather mitigation of HR fault because low frequiences of downstream was significantly less attenuated. Furthermome, 300-511 to 33-299 attenuation ratio was more similar to ratio on other circuits.
HR fault causes higher attenuation on whole band of low frequiences (not only upstream). It is visible on page 2
http://www.elnex.pl/product/attachment/d096f15ee037f5f693e1f7867366a54a/pl_PL/Analiza-petli-abonenckiej-SmartClass-TPS.pdf

Electrically, this type of fault behaves like a series capacitance as illustrated in Figure 7d

Has author of the patent mistaked capacitive fault for high resistance fault ? Does capacitive fault causes SNR margin fluctuations? I've heard merely that HR fault causes.

Best regards
konrado5

[burakkucat]

Let's perform a theoretical thought-experiment.

We start with two brass terminals attached to some suitable insulating material, say ebonite (as used by all the pioneering electrical engineers in the 19th and early 20th centuries).

To those two terminals we attach a "measuring device" which, depending upon its configuration, can accurately measure both very small and very large resistances and capacitances.

We have available a box of "perfect" quality resistors, ranging from 1 Ohm to 10000 MOhms. Each resistor is connected, in turn, to those brass terminals and the reading on the "measuring device" is noted.

We have available a box of "perfect" quality capacitors, ranging from 0.001 pFarad to 1000 mFarad. Each capacitor is connected, in turn, to those brass terminals and the reading on the "measuring device" is noted.

At some point in the experiment with the resistors we will be seeing readings (with the very high resistances, tending towards infinity) that when plotted out against some appropriate ordinate match that of the experiment using the capacitors (with the very small capacitances).

So in our "thought experiment" we see that very large resistances can be approximated by very small capacitances.

Now coming back to the real world of joints in a metallic pathway over which both telephony and xDSL signals are carried. I'll choose the fifth joint counted from which ever end of the circuit that is more convenient. That joint is perfect. To all intents and purposes its resistance is zero Ohms, its capacitance is zero Farads and it is perfectly symmetric in its signal carrying ability. Now, as we are in the real world, that joint can go faulty. It might develop high resistance tendencies, it might become more capacitive than resistive, it might become asymmetric in those tendencies (i.e. become semiconducting). Of those defects the most common is HR, which is then followed (in the order of appearance) by semiconducting.

A HR joint will predominately attenuate across the entire spectrum of interest. A semiconducting joint will predominately attenuate across the entire spectrum of interest and add intermodulation products as a result of combining, asymmetrically, wanted and stray signals. A capacitive joint will selectively attenuate the lower frequencies rather than the higher. All three mentioned defects will attenuate the (wanted) signal but in different ways and, quite often, in frequency dependent fashions.

[4candles]

Bravo b*cat - an exemplary exposition.   

<reverential bow>

[konrado5]

burakkucat: thank you very much for accurate explanation.

A HR joint will predominately attenuate across the entire spectrum of interest. A semiconducting joint will predominately attenuate across the entire spectrum of interest and add intermodulation products as a result of combining, asymmetrically, wanted and stray signals. A capacitive joint will selectively attenuate the lower frequencies rather than the higher. All three mentioned defects will attenuate the (wanted) signal but in different ways and, quite often, in frequency dependent fashions.

How these three kinds of faults affect on service? I've heard that HR faults causes SNR margin fluctuations (especially upstream) and a lot of CRC errros. What about capacitive faults and semi-conducting faults? What about shunt faults ?

Best regards
konrado5