SNR drops as weather gets warmer.

Anyone else noticed this. I am running my SNR target at 1.5db and when it gets cold it can rise to 2.5db, but as the weather has warmed up it has dropped to 1.1db, particularly today. Might have to force a resync unless the router does it itself.

Whens its cold the copper contracts and the line effectively becomes shorter i think.

When its hot the opposite happens and the line becomes longer ?

Not sure

i find my line more stable in the summer.

In reply to a post by DrDeath:

Whens its cold the copper contracts and the line effectively becomes shorter i think.

When its hot the opposite happens and the line becomes longer ?

I see, interesting, could be the reason.

Unlikely given the amount of change in length and diameter.

Even if the change in length made a measurable change in attenuation then the change in diameter along that length would have the opposite effect. Shorten line >>> decrease attenuation. Reduce Diameter >>> increase resistance and thus attenuation!

My line also seems to like the cold!
Perhaps it's down to copper conductivity slightly improving when cold so lowering the attenuation?

Temperature and Conductivity

copper conductivity slightly improving when cold

The opposite I would have thought ie at absoloute zero copper does not conduct.

Ian

dip a copper cable into liquid nitrogen and it will superconduct, it's a property of all metals, increased conductivity at low temperatures.

Always thought this was due to physics, and the laws of thermodynamics. As Anonymous has said, if things are super cooled so they become super conducting, there is no electrical resistance, and because the atoms are hardly vibrating any more (due to heat), there's no 'quantum' fluctuations being generated in the material as noise, so the noise floor of the medium is reduced. If the material is hotter, there is more energy, and so more noise.

In typical UK temperatures - 0^o to 20^o c the difference is about 0.35% per degree C so for a 10^o drop there will be a 3.5% reduction in resistance. But buried cables do not change temperature rapidly! The impedance of the line is not just resistive but complex especially at the higher frequencies. It may have a little effect but not one that significantly improves data rates.

Physics was never my strong point. Thanks for the explanations.

I had noticed a slight increase in sync speeds & SNRM (FTTC) as the weather became colder.

I have hung on to an almost 30Mb sync speed, but my DS SNRM is currently down to 2.7dB.
I expect the connection to re-sync (probably at a much lower speed) if this warmer weather keeps up much longer.