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Attenuation

N/A

Attenuation

Are the numbers below good,

Downstream
Noise margin = 41.5 db
Attenuation =9.0 db
Output Power =17

Upstream
Noise margin =11.5
Attenuation =15.0
Output Power =9
23 REPLIES
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

Attenuation

They are excellent. (except for the upstream noise margin)
You must live very close to the exchange Smiley
N/A

Attenuation

I live about 2to3 hundred yards from the exchange, i thought it was a bit high
also, just got BB installed yesterday and BT said they will be replacing
the outside wiring and will check my connection because they
believe there maybe a fault on it, but it seems to be working okay, but they
know better than i do.
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

Attenuation

It does look as though there is some problem due to the figure quoted with the upstream noise margin only being 11.5 dB.
What I cant understand though why it's not affecting the downstream.
They do of course use a use a different band of frequencies for up and down so the fault could be specific to one frequency band :? but its unusual if it is.

As long as it's working though Cool . All the other figures look very good so perhaps they have now cleared a fault?
N/A

Attenuation

I think it probably is affecting downloading because
I have done some speed tests and I get between
446.5kbps and 463.2kbps I was hoping it would be a
bit better, the BT person thought it was a odd fault also,
he was surprised we never had a problem with
home-highway
Dizzley
Grafter
Posts: 275
Registered: 17-04-2007

Could you please explain what the 4 figures mean

I just want to know how the attenuation figures relate to each other, and typical values for good and bad lines. My friend's BT Voyager Wireless ADSL modem (strange, but that's what they call it Wink ) allows him to adjust the upstream attenuation value. My solwise doesn't. I suppose that allows him effectively to increase the gain upstream to compensate.

Cheers,
Pete
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Attenuation

The ADSL: Understanding Line Loss and measurements tutorial found in the tutorials and FAQs forum may help with your understanding.
Highlighted
Dizzley
Grafter
Posts: 275
Registered: 17-04-2007

thanks, that explains it well

Quote
The ADSL: Understanding Line Loss and measurements tutorial found in the tutorials and FAQs forum may help with your understanding.


Absolutely spot on, old bean.

I am getting downstream attenuation of 21.8dB, noise margin = 41dB so I guess my line is pretty good Cool - hence, my original non-synching router must be goosed not the line. That noise margin (SNR?) seems a bit c*ap though.

Pete
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

Re: thanks, that explains it well

Quote


That noise margin (SNR?) seems a bit c*ap though.



Why? 41 db is brilliant for a SNR it means that your signal is over 10,000 times higher than the noise.

The higher the number on SNR the better the line is.
The higher the number on loss is worse the line is.
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Attenuation

ive got an SNR of 33 but its droped to 28.5 can anyone guess whats happeningSmiley.
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Attenuation

Weather conditions, road works, line maintainance.

28.8 is nothing to worry about, and is still very good.
N/A

Re: Could you please explain what the 4 figures mean

Quote
My friend's BT Voyager Wireless ADSL modem allows him to adjust the upstream attenuation value.


This is a measurement, and unless you have an "elastic" measuring device you cannot have any influence over the value.
Dizzley
Grafter
Posts: 275
Registered: 17-04-2007

Re: Could you please explain what the 4 figures mean

Quote
This is a measurement, and unless you have an "elastic" measuring device you cannot have any influence over the value.


Actually, looking at the user guide and the console page you can increase this setting. It offers a dropdown not a static measurement.. Their user guide suggests that if you cannot achieve sync then you can increase this value and it tweaks the gain up to compensate. Not all routers are the same.

Thanks anyway.

Also thanks Peter, As you say 40dB is quite a good SNR isn't it when I actually apply my brain to what you said. Shockedops:

Thanks all.

Peter
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Attenuation

It is impossible to adjust attuation figures from the router, regardless of what the manual says.

If it allows you to adjust one value to compensate for another, then it isn;t attuation.

Attuation is a property of the cable between you and the exchange, and measures how strong the signal is compared to when it left the BT exchange.

The larger the figure, the more signal that has been lost.

Apply this to a cup of water with a hole in it. Person A has to give the cup to you before you have any control over it. The cup will have lost X amount of volume, and you have no way to adjust how much has already been lost.

In ADSL terms, BT and there network is Person A, and X is the attuation. You can't control the loss.
Dizzley
Grafter
Posts: 275
Registered: 17-04-2007

BT Voyager and attenuation

OK, this is what the BT Voyager 2000 modem with wireless access point offers regarding DSL attenuation:

Attenuation
As we all agree, this is the measured (calculated) attenuation seen on the downstream side. This cannot be changed.

And from the User guide...

Tx Power Attenuation
Only change this setting if your BT Voyager cannot synchronise with the ADSL line (DSL light flashing). Change the value to reduce the transmit power so that your modem can synchronise. The value indicates the level of attenuation (in dB) applied to the transmitted power.
The default value is 0 (no attenuation).


Hence our confusion. So you can change the Tx Power but only by attenuating it (reducing it) in an effort to establish synchronisation. Attenuation can be an action as well as an observed phenomenon.

Let's draw a veil over all this :roll: .

Thanks for all the help,
Pete