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Author Topic: SNR Fluctuations  (Read 6063 times)

Andy

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SNR Fluctuations
« on: November 01, 2006, 03:30:10 PM »

Hi

Any advice appreciated.

I found this excellent site whilst trying to work out why by DG834GT kept losing the internet connection. In recent weeks it does it every hour or so but has never done in the past.

Having seen the article on SNR I checked my stats and find that my SNR is continually fluctuating from 0db to a maximum of around 12db - but it is never stable.

I have microfilters fitted to both phone lines (albeit the cheap one's tiscali sent me when I signed up).

I have read the advice on improving SNR and will be trying some more expensive microfilters but wondered if anyone new why there would be this continual fluctuation.

My stats are as follows at this moment in time!:

ADSL Link                              Downstream      Upstream
Connection Speed                1152 kbps          288 kbps
Line Attenuation                   55.0 db              31.5 db
Noise Margin                         7.1 db                20.0 db

I'm not much of a techie so plain language would help.

Many thanks all
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kitz

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Re: SNR Fluctuations
« Reply #1 on: November 01, 2006, 04:32:25 PM »

Hi and welcome to the forums

Is that every hour on the dot that you loose connectivity..  or just a generalisation.

Dont worry too much about the fact that SNR Margin fluctuates.. its pretty normal with adsl and something that even those on excellent lines also see to some extent or other.

SNR Margin fluctuates depending on what background noise is going on... therefore its quite usual for SNR Margin to drop in the evening when more people are at home using their connections and the more likely hood of interferance from electrical items.
The list of items that can introduce noise on the line is practically endless..  but for eg  microwaves, streetlights, mobile phones etc.

I must admit though that 12dB to 0dB Margin is more fluctuation than I would normally expect to see on a fixed 1Mb line..  are things any better from the test socket behind your master socket?

Your attenuation is in relation to the length of your line.. and therefore should remain fixed.  55dB means that 1Mb speed is the most you will get on traditional adsl.

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Andy

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Re: SNR Fluctuations
« Reply #2 on: November 05, 2006, 10:33:48 AM »

Hi

Thanks for the reply.

In answer the drops occur at anytime and are random and if I sit and watch the SNR stats they just go up and down and are seldom stable.

I was going to try buying some higher quality microfilters - is that a good idea?

As far as the test socket is concerned not sure how to do that, could you let me know please?

Do you think I have correctly identified my dropping problem as SNR issues or could it be something else?

Many thanks

Andy
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roseway

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Re: SNR Fluctuations
« Reply #3 on: November 05, 2006, 11:01:47 AM »

Hi Andy,

I suggest you have a good read of http://www.kitz.co.uk/adsl/lowSNR.htm which explains a lot of what you want to know. Problems with loss of sync are usually caused by noise, and it's often possible to improve performance by attention to your internal wiring and connections.

Eric
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Andy

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Re: SNR Fluctuations
« Reply #4 on: November 10, 2006, 02:09:43 PM »

Hi

Thanks for the advice so far but am still having problems!

I have read the SNR article on here and done the following:

Changed my microfilters to Belkin from the cheap one's my ISP sent me.

I have a microfilter on each of my 3 lines coming into the house; 1 for the house phone; 1 for the office phone and 1 for the ADSL line

I have looked for the test socket but my adsl line does not have one - don't know why?

After installing the new microfilters I did notice a better top end SNR margin of around 15db but it still fluctuates a lot, for example here are readings every 10 seconds as I write this:

0 secs   5.6db
10 secs 5.1db
20 secs 7.6db
30 secs 6.9db
40 secs 6.1db
50 secs 5.5db
60 secs 3.3db
70 secs 8.4db
80 secs 9.4db
100 secs 8.6db
110 secs 7.4db
120 secs 8.1db

I don't know what to do next, I work from home and this is causing major problems now

Is it my Router, BT or my ISP causing the problem?

HELP!

Thanks
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kitz

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Re: SNR Fluctuations
« Reply #5 on: November 10, 2006, 04:36:19 PM »

Hi andy

Unfortunately some lines do have SNR problems, and whilst there are quite a few things that you can do to improve your side of things - sometimes its just down to they way your line is :/

Things like good microfilters, NTE5 adls filtered faceplates (if you knew where the master socket is) and checking out your internal wiring can make a lot of difference.

At 55dB you may be able to get your ISP to call an engineer out to look at your line - there is something that they try to do for long length lines, and they may even fit a NTE5 adsl faceplate for you.  Theres no guarantee on that - but it is worth a try.

The flip side of that is that if the engineer comes out and finds that things are as well as they can be - he may recommend that your line is unfit for 1Mb and reduce you to a 512kbps.  This should improve your stability, but your line will be marked as only capable of 512kbps speeds.

>> Is it my Router, BT or my ISP causing the problem?

Its not your ISP, its not BT as such but it is down to your line conditions.
Some routers have proven themselves to cope with low SNR lines much better than others.
Something that may be worth a try is see if you know anyone that has a DG834x that you can borrow for a day or so, to see if that helps.
The D-Link DSL-G604T is another that seems to do ok as is the Speedtouch 536
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Andy

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Re: SNR Fluctuations
« Reply #6 on: November 10, 2006, 04:48:06 PM »

Thanks Kitz

I called my ISP today as well and they tested the line and found a fault which they have now escalated to BT, so hopefully that may help.

I'll post on how they get on!

Thanks again for the advice, I've at least learnt a lot!

Andy
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kitz

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Re: SNR Fluctuations
« Reply #7 on: November 11, 2006, 01:23:40 AM »

Good Luck - let us know how it goes :)
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