Noise margin drops when phone is active

I don't use my phone much but I've just noticed that when the line is active my noise margin drops from 6db to 5.4db. Considering I have the usual FTTC faceplate, shouldn't that be 'impossible'?

Quite normal.

There's nothing special about the FTTC faceplate, it's just the same as any other filter or filtered faceplate, though it is said that the filter specification is slightly higher.

Mine drops by nearly as much as it did on ADSL2+. I forget what it is, but much more than yours.

I don't think it would be impossible. It is a filtered faceplate. A filter filters things, but doesn't necessarily completely block them.

Is it a cordless phone or a corded one? I can imagine some small 'crackle' noise getting through from a corded one, and maybe quite a bit of low RF noise from a cordelss.

I get a 0.1 drop when my phone is on, nothing tbh.

But what did you get on ADSLx?

'tis nothing Sir. Not worth worrying about.

no filter is 100% and you are changing the system slightly when you pick the phone up.

Okay, thanks chaps. I wasn't worried - just a bit surprised. I actually checked because when I picked the phone up there was a godawful 'modem-like' noise for a couple of seconds. Never done it before and I couldn't replicate it either. No idea if it was at my end or the other. The other caller just heard silence until the fault cleared.