ADSL speeds reduced after fibre comes

I am currently on O2 ADSL2+. Up to a few months ago I got a very stable 10-11Mbs connection with a 42dB line attenuation. The local cabinet was upgraded to fibre in December and I soon noticed my ADSL speed had reduced and it now hovers between 9Mbs on a good day and as low as 6.5. The stats show a high SNR but the FEC errors are very high, millions of them a day, so it is unstable at a 6dB margin.

I suspect crosstalk between lines carrying fibre customers and those on ADSL. I notice on the BT site it indicates an estimated speed for my line of 5-7Mbs, much lower than it did when I checked several years ago. Alternatively of course they may have disturbed the wiring while blowing the cable through. It estimates a fibre speed of around 30Mbs, the cabinet is around 1km away - tempted but I don't really need fibre as I do little downloading.

Have others noted speed deterioration after fibre has gone live in their areas?

10 to 11 Mbps was above expected figures even ingnoring any BT data

In reply to a post by dsergeant:

...
Alternatively of course they may have disturbed the wiring while blowing the cable through ....

The fibre goes nowhere near the existing copper wiring.

You say the stats show a high SNR(M?), but then mention 6dB. Maybe we could see the stats?

What is possible, given the FEC values, is that your connection within the normal cabinet, (the PCP), has been disturbed. But not as a direct result of FTTC.

The fibre goes nowhere near the existing copper wiring.

But it could be pulled through the same duct from the exchange and damage the existing cables ? This happened in my area when another exchange was equipped with ADSL and pulling the connection through the ducts trashed about 10% of the lines due to cable damage.

Current line stats, O2 Wireless Box 2:

Uptime: 0 days, 11:14:01
DSL Type: G.992.5 annex A
Maximum Bandwidth (Up/Down) [kbps/kbps]: 1,200 / 9,587
Bandwidth (Up/Down) [kbps/kbps]: 1,191 / 6,487
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 12.0 / 19.0
Lne Attenuation (Up/Down) [dB]: 25.0 / 42.0
SN Margin (Up/Down) [dB]: 7.0 / 12.0
Vendor ID (Local/Remote): TMMB / BDCM
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 302 / 0
FEC Errors (Up/Down): 36 / 707,535
CRC Errors (Up/Down): 36 / 17
HEC Errors (Up/Down): 68,048 / 11

As you can see, it is currently synching at a 12dB margin. Last year it would sync at 10Mbs with a 6dB margin and rather lower errors (but it now seems pretty stable at 6.5Mbs).

I was wondering more about crosstalk between ADSL and VDSL in the copper cable from cabinet to here, which will now be carrying both types of signal in adjacent twisted pairs. It may also be that the cabling has been disturbed - I think they had some problems running the fibre to the next cabinet down the line which may run in the same duct at the bottom of the road.

As you say, for a 2.8km line 10Mb was quite a lot higher than expected, but something has caused to drop.