Broadband Related > ADSL Issues
Shunt fault?
konrado5:
Some day (year 2014) I've had reconnection when there was pavement resurfacing work. Then my attenuation there was 23.5/20.2 dB instead of standard 25.0/14.9 (standard on D-Link DSL-2740B, now I have Netgear DGND 3700v2). On the next day I've had reconnection again when there was pavement resurfacing work and attenunation came back to standard 24.0/14.9 dB.
I attach two Hlogs on one graph Double_Hlog1.png. The red graph is standard Hlog. The green graph is abnormal Hlog. The undulations and lazy roll around the tone 55 is the effect of measurements errors. The proof is green graph on Double_Hlog2.png which was generated when my target SNR margin was risded from standard 6.0 dB to 15.0/17.0 dB. It is noticable that on green graph there are less undulations.
Why do I think that on my circuit there is capacitive fault? On the red graph on the Double_Hlog1.png there is significant attenuation increase around the tone 210, on the green graph there is significant attenuation increase around the tone 150.
--- Quote --- In other words, downstream attenuation tends to increase relative to the upstream attenuation, resulting in an increase in the attenuation ratio.
--- End quote ---
http://www.google.com/patents/EP2747401A1?cl=en
I think the pavement resurfacing work caused that the shunt fault was slightly and temporary modified (the attenuation increase on the earlier downstream frequency and increasement on upstream (20.2 dB instead of standard 14.8 dB).
What do you think about my hypothesis?
Best regards
konrado5
burakkucat:
It is rather difficult to either propose a cause or to analyse an observed change, for one incident, on one circuit, retrospectively.
However if the cable in question is not ducted but is buried directly in the ground, then any resurfacing work might impose an additional (physical) loading on the cable. Such crushing-like action could conceivably perturb the normal capacitive coupling between the two legs of a pair and, thus, appear as a temporary capacitive shunt across the pair.
So in answer to the question --
--- Quote from: konrado5 ---What do you think about my hypothesis?
--- End quote ---
-- I would say that it appears to fit the observations. Unless there is some other more compelling suggestion, then I would be prepared to accept it as the most likely cause.
konrado5:
There must have been some misunderstanding. I don't think that pavement resurfacing work caused temporary shunt fault. I think that shaunt fault is permanent but pavement resurfacing work slightly and temporary modified the shunt fault effect. I think the shunt fault is permanent because on the standard Hlog graph (the red graph) there is significant attenuation increase around the tone 210 and this increase remain up to the end of graph. Pavement resurfacing work caused to the attenuation increase movement, this increase was around the tone 150 instead of tone 210.
But my observations does not reflect accurately expected result of shunt fault (higher attenuation on higher frequiences). On standard Hlog (red graph) there is also increase around the tones 33-50. On the abnormal graph (green graph) there was significantly lower attenuation on these frequiences. Unfortunately I have not any graph for upstream but the upstream attenuation was 20.2 dB instead of standard 14.8 dB. I conclude that on that day increase around the tones 33-50 was moved to the upstream.
To sum up, I see two frequency ranges with too much attenuation related to the remaining frequencies but pavement resurfacing caused movement these ranges to the lower frequiences. :)
Best regards
konrado5
burakkucat:
I shall have to give your observations and hypothesis some further thought.
What I am finding a little difficult to rationalise is how you can say, with any degree of certainty, that the circuit has a capacitive shunt fault when you are only considering a sample size of one! If you had the equivalent data for, say, one thousand circuits then it would be fairly straightforward to offer up the results of an analysis of all those circuits and, thus, support the claim for a shunt fault. Obviously every circuit has a natural capacitance; a function of the product of the intrinsic capacitance per unit length and the total installed length of the cable.
konrado5:
Sudden attenuation increase around tone 210 (around tone 150 on abnormal Hlog) is reason to think about shunt fault. In this patent there is that on shunt fault there is too high downstream attenuation relative to upstream attenuation. On my circuit there is too high 210-511 tone attenuation relative to other tones attenuation.
Best regards
konrado5
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