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[hake]

Between my house and the cabinet is a 6,000 volt substation.
It's been there as long as the house.  I hadn't given it a thought until one of the excellent PlusNet support chaps spotted it on Google map and drew it's possible significance to my attention.

I have experienced constant if intermittent connection problems ever since I changed from ADSL to ADSLMax seven years ago.  It runs OK for days then SNRM suddenly plunges, CRC and HEC errors explode and my connection slows drastically.  I power cycle the router and everything then works OK, albeit with a reduced downstream bandwidth.

I had already had the downstream minimum target SNRM increased to 6dB resulting in a downstream bandwidth of around 9,600kbps.  This did not reduce the downstream bandwidth sufficiently to ensure stability.  The target SNRM is now increased to 9dB and downstream bandwidth is now 8,400kbps.  I hope that this lower figure will result in better reliability.

I suppose that if bandwidth is too high, i.e. signal at too high frequency, the connection can be too sensitive to interference from such as high voltage AC conductors close by.  I would guess that my copper loop passes sufficiently close to the electromagnetic effects of the high voltage conductors supplying the substation.

There is no point in a high downstream bandwidth if the resulting unrecoverable error rate slows the connection to a crawl.

There is light on the horizon.  My exchange is due for BT fibre later this year and I am only 100 yards from the cabinet.

If we ADSL users don't get problems with rain, then there are problems with REIN.

[JGO]

Two points
 You don't say if phone or electrical cables are overhead or underground which will make a difference. 

A substation shouldn't cause interference if it is working properly. If it isn't then a walk past it with a portable MW radio will confirm and the electrical supply people may regard this as indicating a latent fault i.e. sometime it will go bang. OTOH if it sparks a little when the insulators get dirty but clears with rain this is regarded as normal.

If it IS sparking then since  a spark will cause broadband interferencce, VDSL is a bigger target than ADSL so  if the substation is near the cabinet to house run,  a change to FFTC could well make things worse.

I say broadband interference but it won't be 100% uniform broadband interference so the above are most probable states.

[hake]

Thanks JGO.  Please pardon my ignorance.

The cables are below ground.  What frequency should I tune the radio to please?

[JGO]

You need a starting frequency which doesn't have a strong local station on it. This means somewhere at the 550 kHz end depending on your local stations.  612 kHz has been suggested and it isn't a bad starting point, but local stations are the important constraints.  The bandwidth of an AM radio is about 10 Khz so you can't drop between two ADSL "channels"  which is just as well with the calibration accuracy of an AM radio !!

Bear in mind the radio AVG will wind the gain up so a nearby station can be a convenient reference - if noise doesn't obliterate a weak one then forget it, but if it flattens your local main BBC station  at your home, you have a problem ! 

Of course, if you have rounded up the usual suspects with an I plate etc,  it could be crosstalk from other ADSL !!

[hake]

Thanks JGO.  I use a VDSL iPLate and there is a bell wire filter.  I shall follow your directions with the AM radio.

[hake]

I checked the substation with a MW radio tuned to 650kHz.  No RF emissions from the substation could be heard but walking the path beneath which my copper loop (and of course those of others on the 52 year old urban estate where I live), the radio emitted a load buzz/crackle for at least 100 yards either side of my house and round the corner onto a different street.  The wires run about 15 inches beneath the surface in ducts.  I followed my spur up the lawn to the termination point.  A healthy buzz/crackle can be heard.

I believe that my ADSL does not go to the cabinet about 100 yards down the road as there is no buzz/crackle from the radio when I scan for RF in the vicinity of the cabinet which is on the other side of the road.  In fact there is no audible buzz/crackle on that side of the road at all despite there being telephone cables beneath the pavement.

A considerable improvement to my ADSL+ has been effected by getting the minimum target downstream SNRM to be set to 9dB so the situation is now most tolerable.  My exchange is scheduled for fibre later this year.