Attenuation

[trelales]

1. Can someone please explain what attenuation etc  is?

My router stats tell me I have downstream attenuation at 57db and  noise margin at 10db

                                         upstream attenuation at 15.5db and noise margin at 16db

I'm only getting 1.2meg speed. Which of the above is the problem?

2. In another post, I cannot now find it, someone mentioned getting a professional microfilter. I spoke to my local computer shop and he thought that was a load of b.......

Whos is correct?

[MisterW]

Have a read of this http://www.kitz.co.uk/adsl/linestats.htm , it explains all about attenuation,speed ,SNR and how they are related.
That said your attenuation figures are a little strange, typically the downstream is about twice the upstream. In your case its closer to four times which does tend to indicate a problem somewhere...

someone mentioned getting a professional microfilter.I spoke to my local computer shop and he thought that was a load of b.......

All filters are not equal I'm afraid, some cheaper ones can cause problems. 

[Rik]

Whos is correct?

Us, of course.

Attenuation is the amount by which the ADSL signal is reduced between you and the exchange. The longer the line, the higher the figure will be, an aluminium line will have higher attenuation than a copper one, and a thin copper will be higher than a thick one. A further increase in attention can be caused by the number, and quality, of joints between you and the exchange.

I also have a 57db line and sync at ~3k on Max, ~4k on WBC. Like you, my target noise margin has been raised, in my case to 9db, in your case it's either 9 or 12db. Each 3db increase costs you about 500k of sync speed, so I'm guessing you're at 12db, but it's lower now as more noise if picked up at night.

Where are you measuring that throughput? Ideally, do a BT test as it will give us your profile. If the line's been unstable, that may be below your current sync speed should give you.

As to filters, they are not all created equal, and the best by far of the many I have used is the ADSL Nation xf-1e. On long lines, they can make a significant difference.

http://www.adslnation.com/products/xf-1e.php

[trelales]

The figures are from the netgear router.

At the moment the downstream connection speed is 1792 with attenuation at 57 and noise at 10.

Last year the downstream speed was at c2400 with the same attenuation and noise giving about 2 meg speed. As I'm 3.1 km from exchange I was happy with this.

However in the last 6 months my speed has dropped bit by bit to its present level of about 1.2.

IDnet support have suggested I change the filters and move my router to the main BT input box. I'm wlling to try all these (infact I put new filters on today and the downstram speed increased from 1536 to 1792 but the actual speed was still 1.2.  What confuses me is that in the last 6 months I have done nothing to my system or internal wiring (the latter being renewed about 2 years ago) My neighbours have also seen a drop in speed (different ISP's). This logically, well to me anyway, seems to point to something away from my house eg main BT line but IDnet have said that there is no fault on the line.

I cannot access the BT speedtest website to check my profile (constant error message)but Support said it was 1250. 6 months ago it was 2000.

[Rik]

Lines are degrading, and ADSL speeds have been dropping in general with the uptake of the service, more customers = more crosstalk = lower speeds. A 1250 profile means that at some point you have resynced with a speed of 1728 or lower, so you do want to eliminate all possible local sources before involving BT. That's why IDNet have asked you to move the router.

If speeds don't lick up there, then you need to get hold of an AM, battery-powered radio and de-tune it, so you only have white noise. Follow the path of your phone wiring to the router, and watch out for an increase in the noise. Also check the monitor, PC and router power supply. If you find an increase, that's where your noise is coming from.

After that, if there's still a problem, you can risk getting BT involved.

[Technical Ben]

When it comes to filters, it's the same as everything. Some manufactures make really bad equipment. You don't need to pay over the odds, just get a decent one.

[Sebby]

ADSL Nation XF-1e (or XTE-2005 if you are sighting your router at a BT NTE5) is a good filter.