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Author Topic: Unusual Change in SNR Margin Variability  (Read 420 times)

PjH

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Unusual Change in SNR Margin Variability
« on: February 21, 2017, 09:32:59 AM »

This is my first post to the Kitz forum so please forgive any mistakes or misunderstandings on my part. I'd like your advice on the likely causes of an unusual (to me) change in my download SNR Margin variability. I am used to seeing the expected change from low daytime variation to higher night snr margin variation and the associated reduction in the mean snr margin but this is not what I am talking about. The effect I have seen is an increase in daytime snr margin variation from +/-0.1dB to +/-0.6dB over a couple of weeks. The change in variation occurred betwen mid January 2017 and early February 2017.  I have attached a couple of images from Routerstats Lite for mid January 2017 and early February 2017 to show what I mean. Both are from approximately the same time of day for comparison.

From reading other posts I realise the variation may still be in the 'normal' range. It is the change in behaviour that interests me and where I would like your thoughts. The pattern of the noise/variation looks random to me rather like the night time variation from the solar /radiation belt effect on line noise.

For background I am on ADSL Max, 6km from the exchange on an EO line. Attenuation is 46dB. My router is a Billion 8800NL R2 installed in Aug 2016. It has been running well and I achieved a sync rate of 6.176 Mbps and IPP of 5 over months before Feb 2017. The sync rate dropped to 5.472 Mpbs and the IPP to 4.5 when the variation increased from +/-0.1dB to +/-0.6dB in early February 2017. Nothing was changed in my house's electrical system over this period. I have only four neighbouring houses inside 0.5km and they are second homes that have been unoccupied over the period so no changes there. In my case REIN looks less likely as the cause.

So the question is not whether the noise is 'normal' it is why the variation in snr margin increased over a shortish period. Hope you can help.
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burakkucat

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Re: Unusual Change in SNR Margin Variability
« Reply #1 on: February 21, 2017, 03:48:54 PM »

This is my first post . . .

Welcome to the Kitz forum. :)

I've read through your query and what you have asked makes perfect sense. However I can't offer any possible explanation. So let's see what suggestions other members may make.

[slightly off topic]
As an example, I've attached the SNRM plot for Kitz' G.993.2 circuit. For a long time it has been subject to quite violent oscillations in the SNRM. Then quite unexpectedly, at around 0538 hours this morning, the oscillations ceased.

Try as we might, we do not have any reasonable explanation as to the cause of the oscillations.
[/slightly off topic]
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c6em

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Re: Unusual Change in SNR Margin Variability
« Reply #2 on: February 21, 2017, 05:02:07 PM »

I've seen this sort of thing before
SNR becomes more "spiky" and reduces for the same sync
REIN was the cause.
I traced it to "something" in another house about 0.5 miles away by the usual old way of an old style radio on the AM band and wandering round the area - its rural.
Quite impressive was the racket outside the place
They switched it on at around most days 11am each day as I recall
Eventually it went away - most likely as the wretched bit of kit finally failed/blew up.
Somewhere i might have kept the RS screengrabs......

Ed:
now I remember I looked in detail at it - and it was just affecting a small number of specific tones at specific points up the spectrum (not just a single or small group of tones) which were being hammered - I concluded it was a switched mode power supply on its way to total non functionality.
« Last Edit: February 21, 2017, 05:18:45 PM by c6em »
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c6em

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Re: Unusual Change in SNR Margin Variability
« Reply #3 on: February 21, 2017, 05:13:27 PM »

Here you go
from 2012 ADSLmax on the max sync of 8128

Edit
...and here is the link to the audio of the radio recorded on a laptop outside the BT pole feeding several houses of which one was certainly the culprit.
https://www.youtube.com/watch?v=426W6lDpDCU

« Last Edit: February 21, 2017, 05:45:25 PM by c6em »
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PjH

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Re: Unusual Change in SNR Margin Variability
« Reply #4 on: February 22, 2017, 06:35:58 AM »

Thank you for your comments. I looked again at my record of stats from the Billion 8800NL R2 last night. There was a system event in the period that the snr margin variation increased from +/-0.1 to +/-0.6. On 1 February 2017 the router was rebooted and the sync speed increased from 6.112 to 6.304 Mbps. The snr margin variation increased at this point. The mean snrm fell from the previously rather stable 6.2 to 4.9dB and with the higher variation, evidently this was an unstable situation and the router reset itself on 6 February, syncing at 5.472 Mbps. The mean snr margin rose as expected, stabilised at 9dB for a while before gradually falling away to 7.5dB. However the snr margin variation has remained high at +/-0.6dB and did not revert to the previous stable condition of +/-0.1 expected for the mean snrm of 7.5dB.

There seems to be a router event involved. So perhaps the initial increase in snrm variation was to be expected but the fact it has not subsequently fallen is odd. Any thoughts?
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