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Author Topic: Spectral masks  (Read 429 times)

digitalnemesis

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Spectral masks
« on: November 17, 2020, 12:43:19 AM »

Does anyone know if FTTC cabs apply dynamic spectral masks to lines?


I noticed DLM took action on my line and the SNR increased from 6 to 8 to 10 and now fastpath in around 14 days. Also the QLN has improved in the D2 and D3 bands or maybe someone just had their line disconnected?


I'm not good with words but does BT sort of decrease transmission energy in the upper frequency bands when there is noise and increase it when conditions improve or to improve crosstalk between lines?
« Last Edit: November 17, 2020, 03:32:55 PM by digitalnemesis »
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Weaver

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Re: Spectral masks
« Reply #1 on: November 17, 2020, 02:42:05 PM »

I know nothing about FTTC, have never even seen it, but I have not heard about dynamic spectral masks; I could read through the entire of G.993.2 (VDSL2) but I donít have the energy, Iím afraid.

So youíre getting more hissy noise bursts then probably, pushing the (downstream?) SNRM up that far. The QLN improvement could indeed be a crosstalker going away, as you say, or someone has turned off some kind of electrical equipment that is a noise source.

It has got noticeably colder here, donít know what itís like where you are. The lower temperatures have reduced the attenuation figures on my lines due to lowered electrical resistance, and this has meant faster DSL, up by a total of about 0.6 Mbps to 10.2 Mbps combined total TCP speed tester downstream result / 1.0 - 1.4 Mbps upstream (depending on which speed tester you look at). So Iím wondering if reduced temperatures are having a beneficial effect for you too.
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digitalnemesis

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Re: Spectral masks
« Reply #2 on: November 17, 2020, 03:26:22 PM »

I'm not sure what is going on since it happened very early in the morning. I didn't manually resync the modem, the sync is the same just the attainable went up along with the SNR sharply increasing from from 6 to 8 to 10 at around 4 to 5 am each time within 14 days.
« Last Edit: November 17, 2020, 03:33:07 PM by digitalnemesis »
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Weaver

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Re: Spectral masks
« Reply #3 on: November 17, 2020, 03:45:05 PM »

Sorry, I think I said that backwards back there; your SNRM went up, so noise went down, not up. I was thinking about the target SNRM going up or something, not what you said at all. Duh.  ???  :-[

If there has been no opportunity to resync then the modem would just hang on in there despite the fact that you could force a resync when the noise has now gone down and get a higher speed as a reward. Is that the only reason your downstream speed hasnít gone up?

I have had jumps in SNRM on the upstream on two of my slow ADSL2 lines. One is now mysteriously cured but had a fairly regular diurnal square wave pattern. The other is still at it but has a very irregular square wave with a variable period and duty cycle which are both all over the place, not predicable from day to day.

I take it yours isnít a vertical jump kind of graph? That seems very early for sunrise; the reception of distant radio stations because of ionosphere reflection should go away later in the morning, when the sun is about to come up; perhaps thatís a significant noise source for you, keeping the SNRM lower in the night.
« Last Edit: November 17, 2020, 03:53:35 PM by Weaver »
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digitalnemesis

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Re: Spectral masks
« Reply #4 on: November 17, 2020, 05:32:50 PM »

It's like a sudden sharp rise from 6 to 8 to 10 at around 4 am when it happened. Not sure what is going on since it seems too early for BT to be doing work at the cabinet or for someone to turn off their router. It went back down to 8 yesterday. Never seen this happen before from monitoring my line for years.
« Last Edit: November 17, 2020, 08:55:45 PM by digitalnemesis »
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Weaver

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Re: Spectral masks
« Reply #5 on: November 17, 2020, 07:22:46 PM »

It does sound like my weirdness. See the old threads about my varying SNRM:
    https://forum.kitz.co.uk/index.php/topic,24846.0.html
    https://forum.kitz.co.uk/index.php/topic,24933.0.html
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