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Line Attenuation


Line Attenuation

I was wondering if anyone could help me with line attenuation issue as BT baffle me with BIG words and something which resembles science fiction jargon.

For some reason or other my line attenuation changes dramatically, one day it can be around 50.3 db, the next day 51.6 to 52.4 db and sometimes drops to 45.3 db, I can disconnect, then reconnect straight away and its changed again?
I understand that it will change slightly within a few points of a db but five or 6 db is this not strange.

I was having a probelms with crackle on the line when I was connected to the net and made a telephone calls it hissed and crackled, I rang BT and they ran some tests, I have extension sockets fitted by BT, (We wont go into the fact that BT only cover probelms upto the master socket, even though they fitted the extensions) *@~* ers Anyway they turned up the line gain or something like that and it was cured, the hiss and crackle was gone Smiley Although even since I have had BB, the line attenuation jumps up and down like a crazy rabbit on speed?
I asked BT about this and they told me it was distance to exchange and quality of cables fitted in property. Does my house suddenly up and move closer to the exchange one day and move futher away the next, idiots also does someone rip up my extensions and lay older cables when i'm not looking.

Please could someone try to answer this, also if the line attenuation drops to around 45db and stays steady will I not be able to be banged upto 2meg service or not.

Someday BT will get tech support personel who speak normal language, on that day NTL will have been laid in my area and I will have gone cable... No offence to +net u guys are top notch.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Line Attenuation

You need to have a line attenuation of 43dB or lower to get 2Mbs so even when your line has it's best one, it is still outside the limits for 2Mbs.

It is unlikely the gain was increased on your line as in doing so any noise will also be amplified so I suspect they did something else to cure the hiss/crackling.

What ADSL equiopment are you using to monitor the line conditions? Also what is your SNR and does that fluctuate as much and along with the line attenuation changes?

Lots of things can cause line attenuation to fluctuate but it is unusual to have such big swings. This does suggest a possible bloken or bad connection somewhere between you and the exchange which can be affected by wheather conditions and temp changes. Internal phone wiring can make a different to both line attenuation (although not as much) and SNR figures.

Are you connected to the master socket or an extension socket. If an extension, what do you get if you connect to the master socket and does the fluctuations still occur. Have you tried disconnecting all other phones and monitoring the line stats again to see if they remain static then - agin when connected to the master socket. Also try the test socket behind the user removable lower part of your master socket. Try different ADSL filters. Try using no filters at all and with all other phones disconnected (use an old modem phone cable to connect to the BT socket).

For an explaination on line stats see ADSL: Understanding Line Loss and measurements.

Line Attenuation

Fluctuation in the line attenuation accurs in either the master socket or the extension.
To be honsest I get better results from the extension currently, 50.6 db with SNR margin of 18.4 to 19.1 downstream. Just upplugged it before it was 53.0 db line attenuation with SNR margin of 20.5.
I've treid using five differant mirco filters two which came with voyager 105 modem from +net and two cheap ones which where bad, I bought a top quality rj11 cable to connect router BT sockets and still same results, if fact a cheap rj11 cable give me roughly same results.

I was using the 105 voyager modem but went onto windows XP x64 which at the moment there is little... In fact NO ADSL 64 drivers availble, so I bought an ADSL router of Ebay, from this I can log into the ADSL status and view setting and so.