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Attenuation question

Community Veteran
Posts: 1,160
Thanks: 1
Registered: 01-08-2007

Attenuation question

I've recently changed my ADSL router from my original very basic one (with no configuration controls and which wouldn't let me use PlusTalk VoIP) to a considerably more sophisticated wireless one. When I first installed it, I got a downstream attenuation reading of 34db. Since then, I've taken it off the extension lead I had my old ethernet-only modem attached to, which ran from the upstairs wired-in phone extension in another room, and plugged it into a downstairs wired-in extension and the attenuation has dropped to 15.5db. I'm amazed the extension lead made that much difference to the line attenuation!

I would like to plug it into the main BT socket downstairs but my husband's computer won't support WPA, which I've gone over to from WEP as this new router has a wider coverage than the wireless point I had plugged into my old router. I'm around a kilometre and a half from the exchange as the crow flies, so would it be likely that the attenuation could be any better for that sort of distance if I did plug it into the main socket?
Plusnet user since November 2003
Currently on Unlimited Fibre Extra and Unlimited UK & Mobile Calls
11 REPLIES
ID
Grafter
Posts: 125
Registered: 08-08-2007

Attenuation question

From what i have read on these forums the lower the attenuation the better and the opposite with margin ( signal to noise ratio )
I am currently holding a stable 8meg connection with:

Attenuation Downstrean 36
Margin Downstream 6

Plugging the router into the main socket can help get you better figures especially if you have bad internal wiring / extention leads ect.

hope some of my very limited adsl knowledge helps
willhome
Grafter
Posts: 272
Registered: 06-08-2007

Attenuation question

yep totally right... you want high SNR (noise margin) and low Att.
Community Veteran
Posts: 1,160
Thanks: 1
Registered: 01-08-2007

Attenuation question

I won't bully my husband to update his software to be able to join WPA just so I can plug the router into the main BT socket unless it's going to make a lot of difference. The phone extensions in this house were already installed by the builder when we moved in as its first owners but I was using one of those reel extensions from the only upstairs phone socket, which I had been doing for a few years for dial-up access, so I suppose I shouldn't have been surprised at the improvement.

My downstream attenuation is now, as I say, 15.5db and currently, with a downstream connection speed of 2272kbps, the noise margin is mostly at least 25db which, from what I've read, will drop a fair bit when I get higher speeds (still waiting but have recently put in for a queue jump).
Plusnet user since November 2003
Currently on Unlimited Fibre Extra and Unlimited UK & Mobile Calls
shellsong
Grafter
Posts: 2,191
Registered: 03-08-2007

Attenuation question

You could plug your router into the master socket and run ethernet cables to the relevent computer/s if wireless is a "no go"

Btw I'm a little surprised that your attenuation has gone down to 15.5dB if you're 1.5 Km from the exchange-- I'm about that distance and my attenuation is about 28dB down and 20dB up. Are you sure it's the downstream figure and not the upstream one?
Community Veteran
Posts: 1,160
Thanks: 1
Registered: 01-08-2007

Attenuation question

Yes it's definitely 15.5db downstream and 18db upstream according to the router statistics since I ditched using the extension reel. If that's a good reading then there can't be much loss between the master socket and the wired extension, so I'll keep things the way they are for the time being.

The noise margin is currently fluctuating around 22db downstream and 30db upstream but it always seems to be lower in the evening than during the day.
Plusnet user since November 2003
Currently on Unlimited Fibre Extra and Unlimited UK & Mobile Calls
shellsong
Grafter
Posts: 2,191
Registered: 03-08-2007

Attenuation question

That really is very odd because the stats I've seen have almost always been higher downstream than upstream
Community Veteran
Posts: 1,160
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Registered: 01-08-2007

Attenuation question

Well it is very odd, because this morning it's up to 31db downstream but still only 17db upstream and nothing has changed here as far as I'm aware. I did think that the difference when I moved the router was rather dramatic! When I've finished work this pm I'll experiment with plugging it into all the telephone points, with and without phones plugged in at the same time, compare how the readings come out from each of them and see if I can make any sense of it. The router is a Netgear DG384GT.

One thing with our line is that it runs from one telephone pole to another before it comes to this house as there wasn't a direct way of getting it from the existing pole and BT had to put in an extra one just for us - at no extra cost to us either. Anyway, when the weather is wet and windy we do sometimes get intermittent disconnects, presumably from the rainwater seeping in somewhere along the line.
Plusnet user since November 2003
Currently on Unlimited Fibre Extra and Unlimited UK & Mobile Calls
Midville
Grafter
Posts: 376
Registered: 05-04-2007

Attenuation question

Mine is 11db for Attenuation and 31 db for margin is that good then?Huh
N/A

Attenuation question

I posted a ticket on exactly the same issue a week or so ago and on trawling forums found that there were others with exactly the same symptoms.

The attenuation drops to read EXACTLY 15.5dB. My original attenuation was 32.0dB. I saw people with various other initial attenuations that all dropped to EXACTLY 15.5dB without any change to the SNR. This is of course unlikely and approaching impossible for one line and for many it is impossible.

I got Plusnet to check the line and a woosh test gave, on two different days, 15dB (15.5 according to router) and 32.0dB on the next day.

The monkeys in CSC see nothing strange in this and since I do not lose sync do not believe there is a fault on the line despite the fact this is talking about a change in signal of 50x !!

My guess is that the BT equipment is reporting a different transmitted signal power such that when the router measures the received power, it is a constant?

This happened to me 10 days before I was MaxDSL'ed although for others it appears to have occured after the upgrade. The idiot who looked at the ticket closed it saying that because I was in the first 10 days of MaxDSL the attenuation was expected to vary. (1) the attenuation will not change (2) it happened before MaxDSL but when do they ever read the ticket?

I also have a DG834GT but others on the forums have checked the result with other modems and confirmed the same result.
shellsong
Grafter
Posts: 2,191
Registered: 03-08-2007

Attenuation question

Quote
Mine is 11db for Attenuation and 31 db for margin is that good then?Huh

The SNR is respectable-- on ADSL2+ it could get you over 16Mbps so it'll be fine for MaxDSL or 8Mbps LLU. The only reservation I have is that it could be even better given the low attenuation Wink
Community Veteran
Posts: 1,160
Thanks: 1
Registered: 01-08-2007

Attenuation question

Quote
I posted a ticket on exactly the same issue a week or so ago and on trawling forums found that there were others with exactly the same symptoms.

The attenuation drops to read EXACTLY 15.5dB. My original attenuation was 32.0dB. I saw people with various other initial attenuations that all dropped to EXACTLY 15.5dB without any change to the SNR. This is of course unlikely and approaching impossible for one line and for many it is impossible.

I also have a DG834GT but others on the forums have checked the result with other modems and confirmed the same result.

Very interesting! I'll just put the apparent improvement down to a BT glitch then and just coincidental to when I happened to move the router's position. It did seem odd that it could make that much of an improvement!
Plusnet user since November 2003
Currently on Unlimited Fibre Extra and Unlimited UK & Mobile Calls