> Even at 600m, what sort of attenuation range should we see if we've got relatively good copper all the way?
Probably about 5 - 6 dB, and a lot of envious people.
Max download sync rate is determined solely by the SNR margin. Attenuation is line loss, and remains the same regardless of what speed you sync at. SNR margin is affected more by interference, quality of the copper, etc..
Because higher sync speeds use higher frequencies, they are more prone to interference, and SNR isn't as great. Max DSL works by setting a target SNR margin, e.g. 6dB, that means your line will sync at the highest rate it can achieve whilst keeping the SNR margin above 6dB.
So to try and answer your question, an attenuation vs SNR graph would be difficult, you'd have to define a variable as a constant i.e. sync speed.
What someone has tried to do is a graph of attenuation vs achievable sync speed.. I would imagine target SNR margin is defined at 6dB. Note it's very rough, and assumes good quality cable along the whole route, but you can see, even with 33dB attenuation you should be getting close enough to 8Mb, which is consistent with what I would have expected anyway.
Image from
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