SNR/ Attenuation Before/After

hey (looking back at my previous posts on my SNR/atten)

before ring wire removal

Attenuation (dB): 44.5 / 31.5
SNR Margin (dB): 13.5 / 7.5 (17-19 nights)
500-900kb synch rate


after removal
Attenuation (dB): 60 <<<<
SNR: 12
1.5-1.6mb synch rate



i still am question what has happened, i thaught attenuation was not surpose to change, but i have got + 15 all of a sudden

if this didnt increase so much, then i could be getting 3mb shouldnt i?


any ideas on what has caused this huge jump

There's no way that removal of the ring wire can increase attenuation, so either your router is reporting wrongly or (more likely) there's something wrong with your wiring. The wire you should have disconnected is the one on pin 3 in the NTE5 faceplate. Pins 2 and 5 (only) should be connected. Check that they are correctly connected to pins 2 and 5 in all the extension sockets.

Eric

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then i could be getting 3mb shouldnt i?

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More than that actually, there's someone on this board that has a 57db attenuation line and gets 4mb sync. You should get at least 4.5-5mb i'd say.

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any ideas on what has caused this huge jump

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Yes, you've got a dodgy connection on one of the other 2 wires.

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More than that actually, there's someone on this board that has a 57db attenuation line and gets 4mb sync. You should get at least 4.5-5mb i'd say.

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There's more to line speed than just the attenuation figure. The SNR of the line is just as important. To demonstrate, I have 2 lines in this office, and here are the current stats:

Line 1: Attn: 46dB, sync speed 3360, SNR 5dB

Line 2: Attn: 42dB, sync speed 6112, SNR 4dB

ADSL uses a range of frequencies (bins), each of which has an attenuation figure. The higher frequencies will have a higher attenuation. To get a single figure displayed on a router some kind of average is used.

When the noise on a line decreases more of the higher frequency bins can be used and hence the overall attenuation may rise.

I think you are getting confused. The displayed SNR is the average of all the frequencies used, but the line attenuation is always measured at 300kHz for reference purposes. My SNR goes up and down like a yo-yo, but my line attenuations have stayed static for months.

My SNR gets worse by about 5dB in the evenings. If I re-sync then my speed decreases and the SNR increases again as expected. I also see an increase in my attenuation of between 0.5 and 1 dB.

I only have a basic knowledge about how ADSL works so assumed that the change in my attenuation was due to it being measured at different frequencies. Does the changing attenuation indicate a problem with my line or router?

SNR changes in the evenings are due to the fact that the source of the noise (broadcast stations in the MW band) are much stronger at night, because the layer in the ionosphere which reflects these signals is destroyed by daylight. ADSL uses the same frequencies as MW radio. All you can do is to keep unfiltered wiring above ground as short as possible, to stop it acting as an aerial. I think the variations you're seeing in the attenuation are more to do with the innacuracy of the measurement as anything else.

Edited by deleted (Wed 25-Oct-06 15:12:50)

Yes, I was aware why SNR gets worse in the evenings. The information that lead me to believe that attenuation was measured at different frequencies came from this post. Perhaps different routers derive the figures in different ways, or perhaps it is just an inaccuracy as you suggest.

So would a 5dB drop in SNR from day to night be typical?