Hi
nick-in-montgomery wrote:Hello,
Today I installed my new 7800DXL to replace my trusty 7800, all is going swimmingly!
Just a quick query though, my old 7800 reported the attenuation on my long (4.8km) rural BT line as 63db, my new 7800DXL claims it is only 53db! I'm not complaining of course, it just seems a bit odd. BT claims I should not be able to exceed 1.5Mbps but with some tweaking the data rate seems to vary between 2.4Mbps and 3.1Mbps depending on the weather (I kid you not, this is Mid Wales after all).
Can anybody explain this?
Nick
Attenuation as reported by the router isn't the same figure used by BT and can't really be used to indicate very much, and a lower attenuation reported from the modem may be a sign of a worse connection not better.
True attenuation is measured using a fixed frequency, I think it's 300kHz.
Attenuation shown by modems is usually some fudged figure based on the average of all frequencies over the entire range received to give some overall figure. Different boxes calculate this differently as well.
If we assume both the 7800 and DXL are calculating the attenuation exactly the same way, then the lower attenuation reported may indicate a poorer performance. This is because the 7800 older model was hearing higher weaker frequencies that had higher attenuation, so pushing the reported average higher. Whereas the newer model just can't hear those higher ones or can't use them, so it's average is reported lower.
It wouldn't surprise me if the DXL doesn't perform quite as well, this is because the ADSL chip that used be separate from the main processor on the older 7800, and so better isolated from the noisy digital CPU as it was phsyically away from it, is now all one chip to make things cheaper!
However it is very difficult to know for sure without seeing some like a bit loading chart from each using something like DMT, as it just might be reporting differences in the software.
Edit: Just to add that a telephone lines attenuation is fixed, it cannot be made better or worse by the kit sat at either end as attenuation is a physical property of the wire itself. The only way the lines attenuation can be changed is by some physical change to the wire itself, for example better cable is installed or some changes mean your telephone line is now taking a shorter or longer route to.
Regards
Phil