Need some ADSL technical questions answered ...

[adamr]

Morning Forumites ...

Need ur peoples help please

1. For ADSL what is the noise threshold on the line to be measured?
2. How does capcitance and bridge taps affect ADSL ... ?
3. Can a normal fluke meter be used to measure both these conditons on the line. Or is this not a true ADSL test? Or do we need to measure each individual carrier in the ADSL frequency spectrum?

 

[krycor]

wow.. hard questions I only know that for point 2 with bridge taps, Telkom would remove if possible or something cause it degrades the adsl quality as it causes self interference as some of the adsl signal gets bounced back, worse if the point is closer to the end point.

 

[moron51]

Itu G.992.1

Good question, as they say in the classics!
Wikipedia has quite a bit on the ADSL spec (ITU G.992.1), here:
http://en.wikipedia.org/wiki/ITU_G.992.1

It makes the point that the signal-to-noise ratio may not drop below 6dB in ANY of the 256 frequency bins.

I assume that excessive capacitance on the line will attenuate the higher frequencies (downstream side), while bridge taps sound like they have the potential to generate reflections on the line.
I suspect that Telkom's old local loop cables add the problem of crosstalk, contributing to the degradation we see during the early evening "prime time", when connections that were stable during periods of low usage, start to fall over.

Before you connect your Fluke to the line to measure impedance, check the line voltage, and make sure that your multimeter can measure on live circuits with DC present.