In reply to a post by billford:

In reply to a post by BatBoy:

Oh I get it

No you don't.

Yes I do. This is the post I was referring to, not some theoretical discussion involving Fourier

In reply to a post by billford:

lower speeds give lower attenuation

- which is totally wrong.

In reply to a post by BatBoy:

In reply to a post by billford:

lower speeds give lower attenuation

- which is totally wrong.

In reference to www.kitz.co.uk/adsl/linestats.htm#attenuation:

Because the router measures against the frequencies available, some users may notice a very slight increase in attenuation if say moving from a fixed rate 512 kb connection up to 2Mb.
Higher frequencies such as those used to transmit faster speeds are more likely to be attenuated (higher frequencies = higher attenuation).
ADSL 2+ has an increased frequency spectrum, therefore an increased attenuation of around 3-4dB is not unusual. As a very rough guide a speed increase of 4Mb is said to increase the attenuation by 1dB.

In reply to a post by billford:

ADSL 2+ has an increased frequency spectrum, therefore an increased attenuation of around 3-4dB is not unusual

This is because the frequency range is doubled therefore the attenuation is also doubled.

In reply to a post by BatBoy:

This is because the frequency range is doubled therefore the attenuation is also doubled.

Ah, I see... so increasing the frequencies in use leads to higher attenuation, but lowering the frequencies in use doesn't lead to lower attenuation.

I'm most grateful for your insight.

In reply to a post by billford:

In reply to a post by BatBoy:

This is because the frequency range is doubled therefore the attenuation is also doubled.

Ah, I see... so increasing the frequencies in use leads to higher attenuation, but lowering the frequencies in use doesn't lead to lower attenuation.

I'm most grateful for your insight.

The frequencies are fixed, changed only by switching from ADSL to ADSL2+. Therefore the attenuation is fixed for ADSL and it is fixed for ADSL2+.

In reply to a post by BatBoy:

The frequencies are fixed, changed only by switching from ADSL to ADSL2+. Therefore the attenuation is fixed for ADSL and it is fixed for ADSL2+.

The available frequencies are fixed, which ones are actually used depends on the negotiated sync speed.

In reply to a post by billford:

In reply to a post by BatBoy:

The frequencies are fixed, changed only by switching from ADSL to ADSL2+. Therefore the attenuation is fixed for ADSL and it is fixed for ADSL2+.

The available frequencies are fixed, which ones are actually used depends on the negotiated sync speed.

The available frequencies are used to calculate the attenuation.

In reply to a post by BatBoy:

The available frequencies are used to calculate the attenuation.

No, the actual frequencies are used to measure the attenuation.

Calculation of the attenuation of a phone line possibly several kilometers long, with unknown properties, over a range of frequencies is not a practical proposition.

In reply to a post by billford:

In reply to a post by BatBoy:

The available frequencies are used to calculate the attenuation.

No, the actual frequencies are used to measure the attenuation.

Calculation of the attenuation of a phone line possibly several kilometers long, with unknown properties, over a range of frequencies is not a practical proposition.

The reported attenuation is a result of a calculation.

In reply to a post by BatBoy:

The reported attenuation is a result of a calculation.

Of course it is.

The attenuation at a range of frequencies is measured, a (probably weighted) average is calculated and the result given.

If certain frequencies, or a range thereof, aren't used then they don't provide an attenuation figure and don't contribute to the reported average.

The important point is that the individual attenuations for each frequency are measured, not calculated.