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[GaryW]

As common mode EMI is a bad thing, I guess common mode EMI filters must be a good thing    The only inline filter I've been able to find is from a company called Coilcraft who don't seem to have any stock in the UK:   https://www.coilcraft.com/pdfs/modjack.pdf

Does anyone know of an alternative source of this kind of filter?

[johnson]

Feed the cable through a spare ferrite ring maybe? 

But seriously, dont almost all filtered faceplates have one already?

This is one on the guts of a mk2 faceplate:
https://imgur.com/a/A2e3U0M

[GaryW]

Feed the cable through a spare ferrite ring maybe? 

But seriously, dont almost all filtered faceplates have one already?

This is one on the guts of a mk2 faceplate:
https://imgur.com/a/A2e3U0M

Fair point that filtered faceplates do have one, but if they're cheap enough it's worth trying    After all, there shouldn't be any need for microfilters with a filtered faceplate, but adding a few on the phone line does improve snrm a little (and reduce the amount it oscillates) - at least it does on my line and with my DECT phone, and others have found similar improvements.

[johnson]

Dont get me wrong, I'm all for trying it. Just finding a filter that doesnt do more harm than good is probably tricky.

[Black Sheep]

Yeah ..... the idea is admirable, but believe me ..... all avenues regarding this subject have been explored, I suspect ??. 

Wouldn't want you wasting your time and money.

[spring]

http://whrl.pl/RbTWf4

Tried the C10 and Jacksons and an HPM RFI and EMI filter, even shielding on the phone line, baums, load balancers and ferrite cores in desparation but ACS brand inline filter for some reason just cuts it above all the rest and is better alone on the line.

Dunno what an inline filter means there but I hope it helped.
Edit: Seems the VMG1312/8324/8924-B10A have it, for example. If an inline filter on the way to the modem can be improved/added (no idea), it should help with errors but from my knowledge has the effect of slightly "extending the line", so the "max attainable sync" would be from an irrelevant bit to a considerable bit lower. But, it's proven to help with errors, and its impact on real-world speed can be positive, if there were errors at the current sync, or preventing from syncing higher. (or if it's a bad filter, it might only be detrimental to everything ).
See also: https://kitz.co.uk/adsl/rein.htm

Edit2: @j0hn True, but a filtered faceplate also has an inline filter. I wasn't suggesting what filter to buy. AFAIR, I'm still using ADSL2 filters on my VDSL2 and have the stats you've seen. Seeing what this guy said, it makes sense.

[j0hn]

I believe they are discussing filters for ADSL/ADSL2.

Just a heads up for anyone thinking of trying them... picking a random sized ferrite core and sticking it on your DSL cable will likely do nothing.

There are different grades of ferrite with different RF properties. You need to buy the correct size ferrite ring for the specific frequency you need. You then need to "turn" the ferrite ring the correct number of turns needed.

The chances of a random ferrite core used for audio equipment having any kind of positive effect on the DSL circuit are very slim indeed.