Kitz Forum
Broadband Related => ADSL Issues => Topic started by: Weaver on March 25, 2019, 06:49:26 PM
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Here is an extract from the SNRM vs freqency data obtained from my modem. DSL tone numbers vs SNRM. See the peak at tone 125:
113 22.9375
114 22.8125
115 22.3750
116 21.8125
117 21.1250
118 21.1250
119 20.3750
120 19.8750
121 18.3750
122 17.7500
123 13.0625
124 10.5625
125 8.8125
126 11.3125
127 13.7500
128 15.1875
129 15.1250
130 16.2500
131 16.1875
132 15.8750
133 15.1875
134 15.3750
135 15.1875
What could that be? That would equate to what -539 kHz?
Thing is, I can’t see a corresponding thing in the QLN.
That doesn’t prove that it is noise as it could be reduced received signal level too - frequency-dependent increased attenuation, a loss of power or cancellation - is that even possible?
What am I looking at?
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The extract you have shown is not of SNRM but SNR per sub-carrier.
Let's check the calculation . . . 125 x 4.3125 kHz per sub-carrier = 539.0625 kHz
Either the signal strength has been reduced or the "noise" strength has been increased. You will be looking at a dip (not a peak) in the SNR plot. What is shown in the bit loading plot for that frequency?
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Sorry, brain error regarding SNRM, I wasn’t thinking straight but I suppose that I could have realised that that didn’t make sense if I had bothered to engage brain first. I’m glad you pointed that out. ???
What is odd is that I can’t see any corresponding ‘feature’ in the bit loading. I’ve just rechecked and it’s just featureless, gently declining monotonically, as we expect.
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I have also checked for usage of that frequency by broadcasting stations and could only find a Belgian station. I think that can be ruled out!
As there is no corresponding perturbation in the bit-loading and QLN plots, I suspect it is going to remain a mystery.
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I found the Belgian station too.
What is you opinion of the width of the anomaly? It does not seem to be quite a sharp peak as we usually see because there is some region around it which is more cone-like, roughly 3dB per tone spacing over several tones in either side.
I am quite baffled.
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Do you see the same on all your lines?
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What is you opinion of the width of the anomaly? It does not seem to be quite a sharp peak as we usually see because there is some region around it which is more cone-like, roughly 3dB per tone spacing over several tones in either side.
Not having sight of the plot, it is rather difficult for me to comment. :) However the preceding question (above) is relevant. Is the anomaly "present and correct" on all four lines?
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On line 1 there is a tiny 3dB deep depression centred on tone 102, again cone-shaped/symmetrical-triangular.
On the other lines just some minor irregularities.
So the original pattern has vanished altogether. It was just an unidentified fleeting artefact. :-[ ???
It felt very fishy given that I could not match it against other stats in the same modem.
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b*cat nods, knowingly. There are so many temporary, minor, perturbations in the average xDSL circuit's statistics that it is best to view the data with an "it may not be explainable" mind-set.
I hardly ever look at my own . . . as long as the service works, I just make use of it. :)
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Quite so. It was the depth of it that led me astray though in this case. Weird.
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Back of a fag packet calculation for your 539Kz Quafor Poobel Belgie. Belgian haircut of BINs
You have Belgian squatters in BIN 125 with their belongings scattered either side.
If you evict them, make line longer or shorter, they will only move BIN along with there tat.
Unless the router or house wiring etc are picking up 539KHz or it's harmonics you can't fix it.
Rough harmonic calculations.
Integers are bad news.
Line length 7000M
539 = 12.98
417 = 16.78
348 = 20.11
270 = 25.92
139 = 50.35
Line length 7007M
539 = 13.00
417 = 16.80
348 = 20.13
270 = 25.95
139 = 50.41
Line length 7100M
539 = 13.17
417 = 17.02
348 = 20.40
270 = 26.29
139 = 51.07
I suspect you are 7.007Km from the exchange.