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Author Topic: Sudden SNRM drop - causes?  (Read 1069 times)

jelv

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Re: Sudden SNRM drop - causes?
« Reply #15 on: October 18, 2018, 09:15:12 AM »

Do you know where the route of the new line departs from the other three? Obviously you need to start thinking about any businesses from that point onwards.

Thinking about the times: a restaurant with a noisy extractor fan? Looking at Google maps at what could be the route: Claymore doesn't seem to open early enough, Creelers shuts too early. If you think of any likely candidates it mike be worth ringing them to ask if they turn something on/off at the right times.
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johnson

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Re: Sudden SNRM drop - causes?
« Reply #16 on: October 18, 2018, 04:39:21 PM »

Interesting! I wouldn't worry too much about the drop, once you have made certain there are no devices on the property that run on such a time frame there is likely little you cant do about it. If it was causing a resync then maybe further investigation would be worth it, but for now at least you know the best times to choose to resync.

Here is a new graph image.

So combining both up and downstream, the best time is between 7AM and 11AM. There is a good 2db of wiggle room left at the worst points of the night on the downstream, so I guess a forced 1db reduction might be viable:

Code: [Select]
xdslctl configure --snr 80

I believe 80 gives just over a 1db reduction in target, so thats what I'd do in the 7-11 time period and monitor further.
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ejs

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Re: Sudden SNRM drop - causes?
« Reply #17 on: October 18, 2018, 06:12:55 PM »

Am I the only person who thinks that some supposed interference source that only affects the ADSL upstream seems quite unlikely?
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johnson

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Re: Sudden SNRM drop - causes?
« Reply #18 on: October 18, 2018, 06:40:48 PM »

You mean because anything putting out enough RF to cause this in the upstream should be having a similar impact on the down? I guess so.

But what are the other possibilities? I'd be worried there was some glitch with the graph if it caused exact round number changes or happened dead on hours, but to the best of my knowledge the graph is exactly what the modem is reporting.

Upstream on ADSL2+ is up to what ~ 140khz, right in the band for most SMPS... although I agree in my experience a PSU putting out noise will cause interference at many higher harmonics as well.
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Weaver

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Re: Sudden SNRM drop - causes?
« Reply #19 on: October 18, 2018, 11:56:43 PM »

Given that it is only affecting lower frequencies, this could be a very narrow frequency source. Talking about the cable run, the Claymore restaurant might be near where the cable goes, I am not sure where it crosses the main road from the north to south side if it is not on the south side all the way, which it might very well be.

I don’t understand how there can be much difference in the placement of the newer line compared to the previous ones as they are all heading back from the same place to the one and only exchange.

It is very weird that it is not seen on the other line.
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Weaver

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Re: Sudden SNRM drop - causes?
« Reply #20 on: October 19, 2018, 03:54:37 AM »

Today’s graph - not quite such a simple regular pattern
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Weaver

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Re: Sudden SNRM drop - causes?
« Reply #21 on: October 19, 2018, 04:03:46 AM »

Thinking about businesses etc - Creelers’ restaurant is nit that near to the main road, it is a little way off, on a side road. There is the village hall, primary school on the south side of the main road and on the north side there is a large petrol station and a sizeable supermarket and car parking. The Supermarket and petrol station will have all sorts of electrical activity going on. I am wondering if some of the cables from the exchange run along the north side of the main road and some along the south side. We were told - see earlier threads - that a pair had been brought into service from some other bundle and it sounded as if there were enough pairs going from the main road to Heasta but not enough going along the main road from the exchange (west) towards the PCP very near (to the west of) the Claymore restaurant where the Heasta road meets the main road.

[Moderator edited to correct an "autocorrect generated typo".]
« Last Edit: October 19, 2018, 06:07:22 PM by burakkucat »
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johnson

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Re: Sudden SNRM drop - causes?
« Reply #22 on: October 19, 2018, 04:46:13 AM »

The plot thickens! Certainly seems like business hours for a restaurant or service station, will be interesting to see if it changes over the weekend.

And you are seeing no similar dips on the other lines?
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Weaver

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Re: Sudden SNRM drop - causes?
« Reply #23 on: October 19, 2018, 06:26:47 AM »

Still no such activity on line #3. Yet to install monitoring on the final two modems but will do so ASAP.
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Octal

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Re: Sudden SNRM drop - causes?
« Reply #24 on: October 21, 2018, 05:12:26 PM »

Have you tried listening on a good old AM radio receiver to see if it picks up any electrical noise? If it does you can use it to direction find the source.
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Weaver

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Re: Sudden SNRM drop - causes?
« Reply #25 on: October 21, 2018, 10:31:31 PM »

If someone were roaming around with a radio, they would have to somehow be close to line 2 but not to line 3.
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Weaver

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Re: Sudden SNRM drop - causes?
« Reply #26 on: November 24, 2018, 06:21:41 PM »

And then it all changed, because the more recent total weirdness is now seen on line #3.
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