Yes i agree, it isn't the density of amateur operators so much as the power levels induced into telephone lines. They may be narrow band but the receivers in VDSL chipsets can only cope with so much common mode before the LNA saturates. They are after all a wide open receiver for the entire shortwave band as mooted.
So although the narrow band interferer seems nothing to worry about , it could in fact block VDSL modems for some radius around it.
It is something to consider as it was less of an issue with ADSL but is a reality for VDSL .
The converse issue is the potential for a lot of angry amateurs when the noise floor on the HF bands rises to an unusable level due to all the open wire radiators (phone lines) spewing out loads of narrow band OFDM carriers across the whole band.
Homeplugs cover both issues above as they are basically VDSL modems transmitting into an open line/aerial, the mains. Their effect on FTTC/VDSL though will probably only be an issue for houses/businesses that have their phone lines running parallel to mains cables, like in trunking or along a wall etc..
Or if overhead phone lines, the incomer runs alongside mains cables to its destination in the property.
I concur on crosstalk being the major issue, vectoring will improve the speed of those on short lines (< 1km) , after this cancelling out interference that is stronger than the desired signal isn't going to work. Especially as the longer lines in a bundle will of experienced crosstalk from all the closer pairs it encounters on its travels.
VDSL is akin to ADSL , it is a way of extracting more use out of existent copper infrastructure investment and for short distances it works. But it is always going to be an analogue medium that with all the best intentions will suffer real world issues relating to interferers/noise/poor cables/corroded joints etc..
The fact it is marketed as fibre broadband and without complaint i find quite remarkable as it is no more Fibre than ADSL was. Just the termination point is a green box, not a DSLAM in the exchange.
On that basis Fixed Wireless is Fibre too
The density of radio amateur operators is very low and their periods of operation usually fairly short. Amateur transmissions are narrow band and far lower power than commercial transmitters - voice will be 3kHz tops and a maximum of 400w PEP in the UK. Digital modes and CW (morse) are typically much narrower bandwidth - often just 30Hz or even less and much lower power too. WSPR uses just a few Hz and there have been regular UK - Australia / New Zealand contacts on powers as low as 1mW.
Homeplugs certainly radiate using the house wiring as an antenna and can annoy short wave listeners (they have notch filters to avoid amateur radio bands) but I doubt you'll find anybody who will see higher speeds if they turn theirs off - unless they are faulty.
The big issue with ADSL is always pickup of MW am transmissions after dark and then mainly on ringwires which are not decoupled from the signal pair. Common mode pickup on overhead cabling is less of a problem as can easily be checked by ensuring the ringwire is decoupled when a far smaller noise margin swing will be seen. That will always be the case with engineer installed FTTC.
I won't say there are no other sources of electrical noise impacting VDSL but I strongly suspect that crosstalk will be the biggest which is why BT are looking at vectoring.
Bill Lewis - MD
Fixed wireless ISP - ISPA/CISAS/RIPE member