Engineer has been and gone. Good news and bad news.
No problems with internal wiring.
Found wideband noise was 38db.
Put my line on a new card at the DSLAM.
Wideband noise now -40s to -50s.
Connection speed now at 71 Mbps ish.
However, I had one single speedtest reach 70 Mbps, but any further test since then is back to 56 Mbps. I'm plugged into the master socket with ethernet to my iMac.
I'm now suspecting it's my ageing iMac (24" early 2008) that's the bottleneck. It has 1000BaseT ethernet. Can't check with my iPhone 5 because the wi-fi only goes up to about 40 Mbps. Can't find anyone I know with a computer to test my line.
Plusnet Hub One reports this:
1. Product name: Plusnet Hub
2. Serial number: xxx
3. Firmware version: Software version 4.7.5.1.83.8.226 Last updated 01/10/16
4. Board version: Plusnet Hub One
5. DSL uptime: 0 days, 00:20:37
6. Data rate: 20000 / 72643
7. Maximum data rate: 23939 / 72704
8. Noise margin: 6.8 / 6.0
9. Line attenuation: 10.1 / 11.6
10. Signal attenuation: 10.0 / 11.7
11. Data sent/received: 398.1 MB / 2.2 GB
12. Broadband username:
[email protected]
13. 2.4 GHz Wireless network/SSID: xxx
14. 2.4 GHz Wireless connections: Enabled (802.11 b/g/n (up to 144 Mb/s))
15. 2.4 GHz Wireless security: WPA2
16. 2.4 GHz Wireless channel: Automatic (Smart Wireless)
17. 5 GHz Wireless network/SSID: xxx
18. 5 GHz Wireless connections: Enabled (802.11 a/n/ac (up to 1300 Mb/s))
19. 5 GHz Wireless security: WPA2
20. 5 GHz Wireless channel: Automatic (Smart Wireless)
21. Firewall: Default
22. MAC Address: 90:4d:4a:3e:0b:84
23. Modulation: G.993.2 Annex B
24. Software variant: AA
25. Boot loader: 1.0.0