Right, Thanks for the info. So really you can only rely on trial and error.

If you just want a rough idea it's perfectly reasonable to make some approximations and assumptions, as Kitz's (and others') calculators do, but if you want an accurate answer then yes, it's suck it and see.

And I haven't even mentioned external interference- if your line is overhead and you live near a radio transmitter for example, then the theory goes straight out the window

In reply to a post by billford:

lower speeds give lower attenuation (ignoring differences due to different ways of measuring it).

How can that be true? The attenuation is a function of the line length and the frequency it's measured at, regardless of speed(? I guess you mean bandwidth?). If the frequency is fixed as per Kitz, then the length of the line must be varying

In reply to a post by BatBoy:

(? I guess you mean bandwidth?)

No, I meant speed- reported sync speed.

If we're in pedant mode, I suppose I should have said "maximum data rate" as it's reported in Kbps (or Mbps). Bandwidth is reported in kHz (or MHz).

In reply to a post by billford:

In reply to a post by BatBoy:

(? I guess you mean bandwidth?)

No, I meant speed- reported sync speed.

If we're in pedant mode, I suppose I should have said "maximum data rate" as it's reported in Kbps (or Mbps). Bandwidth is reported in kHz (or MHz).

Bandwidth has several related meanings:

Bandwidth (signal processing) or analog bandwidth, frequency bandwidth or radio bandwidth: a measure of the width of a range of frequencies, measured in hertz

Bandwidth (computing) or digital bandwidth: a rate of data transfer, bit rate or throughput, measured in bits per second (bps)

I think we all mean Bandwidth (computing)

Note that in textbooks on wireless communications, modem data transmission, digital communications, electronics, etc., bandwidth refers to analog signal bandwidth measured in hertz�the original meaning of the term. Some computer networking authors prefer less ambiguous terms such as bit rate, channel capacity and throughput rather than bandwidth in bit/s, to avoid this confusion.

Edited by billford (Sat 11-Jun-11 13:34:48)

In reply to a post by billford:

Note that in textbooks on wireless communications, modem data transmission, digital communications, electronics, etc., bandwidth refers to analog signal bandwidth measured in hertz�the original meaning of the term. Some computer networking authors prefer less ambiguous terms such as bit rate, channel capacity and throughput rather than bandwidth in bit/s, to avoid this confusion.

Yeah, I understand it was the original meaning, however those days have gone.

Now, back to the point - how can the speed affect the attenuation?

In reply to a post by BatBoy:

Yeah, I understand it was the original meaning, however those days have gone.

But the ambiguity remains... so if you want to try pedantry, do it properly.

Now, back to the point - how can the speed affect the attenuation?

Higher data rates require the inclusion of higher frequencies (cf Fourier). In ordinary cable such as used in telephone lines the higher frequencies are attenuated more than the lower ones for a given cable length. Electromagnetic radiation, capacitive/inductive losses, skin effect... it's not rocket science, just basic physics.

So higher data rates result in a higher overall attenuation.

Edited by billford (Sat 11-Jun-11 13:47:33)

In reply to a post by billford:

In reply to a post by BatBoy:

Yeah, I understand it was the original meaning, however those days have gone.

But the ambiguity remains... so if you want to try pedantry, do it properly.

Now, back to the point - how can the speed affect the attenuation?

Higher data rates require the inclusion of higher frequencies (cf Fourier). In ordinary cable such as used in telephone lines the higher frequencies are attenuated more than the lower ones for a given cable length. Electromagnetic radiation, capacitive/inductive losses, skin effect... it's not rocket science, just basic physics.

So higher data rates result in a higher overall attenuation.

Oh I get it, you're off into a theoretical discussion. I was talking about the OP's experience.

In reply to a post by BatBoy:

Oh I get it

No you don't.