I have an interesting frequency blip on my VDSL2 and I was hoping that somebody might know what on the line would cause that particular shape on the tone graph. I do understand how VDSL frequencies are layed out and what BINs and BITs are but this little blip is a mystery to me. The screenshots shown are from my 2860 and the 2860 we have at our office. Both are served by 80/20 synced VDSL2 lines and are quite close to the cabinet. Both have clean wiring and are filtered at the master.

DSLs both work perfectly but in tracking down other problems I have come across this and it is now bugging me.

My DSL with the 'feature' marked with red: -


Office DSL, for comparison, does not exhibit this: -


It looks to me that the odd quality problem happens in the portion of the spectrum used for ADSL1 but again I have no idea why.

My DSL wiring goes: CABINET --> 50m straight along under pavement --> Concrete Junction Box ->> 6m straight (continuous) cable to house --> 3m cable to BT Mk3 filtered master --> 2860

Office DSL wiring goes: CABINET --> unknown short length --> 20 pair into building --> 10m CAT5 to BT Master + ADSL Nation hardwired filter --> 2m CAT5 --> patch panel --> 2860

Your images are missing so it's hard to say.

AdrianH54 wrote: Your images are missing so it's hard to say.

Ooops! Sorry everybody on IPv4, so most people. Forgot to send the images to my IPv4 host, should be there now. Bit of a "kick myself in the foot" move that!

My 2860 has the same "blip". No VDSL issues here and like you I'm close to the cabinet (less than 100m)

I'm not sure, but i think it indicates a 'bridge tap' on the line, where a 'T junction' of twisted pairs has the effect of introducing a high attenuation over a range of frequencies. I don't what frequencies the bin numbers correspond to, though.

I have this effect as well, but my line is so long I don't see anything past bin 600 downstream, and only the first two bars upstream

bridge tap

Now that could make some sense. The 2 lines I see this on are residential and in older cabling areas where party lines were common. I think we had a party line back in the 70's, though the fibre connection is on a newish line, who knows what the street cabling does. The 3rd connection, where I do NOT see this is a newer cabling run into a small industrial estate and would have been very unlikely to have anything other than a straight run.

I was also toying with the idea of cross talk from ADSL2 lines close by.