ADSL Interference from electricity supply systems

Does anybody know about the workings of the UK mains distribution - or
suggest a group where electricity supply professionals hang out ?

It's a problem I've been chasing for ages - bursts of high errors for a
single period of several minutes between 17:00 and 18:30ish. Its not
local RF interference - I've ruled that out in this case. Absolutely
nothing untoward heard on the phone line during these episodes. I'm
beginning to think it might be connected with the peak in mains load
around teatime, causing tap changes on substation transformers - or
something.
RF carrier telemetry signals on the mains ? Earth leakages ? (I know
naff all about heavy current engineering, so forgive the ignorance).

The reason I suspect this is because :
1 The timing, as detailed above.
2 The BT cabinet in my cable routing is just a few yards from a substation.
3 It looks as if the BT cables run very close and parallel to the HV
mains cable.

Any views ? (I've run out of other ideas).

John Livingston

How have you ruled out local RF interference?

What if your cooker oven or a neighbours has a faulty thermostat which
generates RF interference noise and the mains and phone cables are near to
each other?

Or it could be related to the street lighting coming on.

Have you been to:
http://www.dslzoneuk.net/forum/viewforum.php?f=24 and gone to "improve your
speed."

This procedure if you have not done it will reduce your susceptibility to
noise pick up.

Alec


"John Livingston" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Does anybody know about the workings of the UK mains distribution - or
> suggest a group where electricity supply professionals hang out ?
>
> It's a problem I've been chasing for ages - bursts of high errors for a
> single period of several minutes between 17:00 and 18:30ish. Its not local
> RF interference - I've ruled that out in this case. Absolutely nothing
> untoward heard on the phone line during these episodes. I'm beginning to
> think it might be connected with the peak in mains load around teatime,
> causing tap changes on substation transformers - or something.
> RF carrier telemetry signals on the mains ? Earth leakages ? (I know naff
> all about heavy current engineering, so forgive the ignorance).
>
> The reason I suspect this is because :
> 1 The timing, as detailed above.
> 2 The BT cabinet in my cable routing is just a few yards from a
> substation.
> 3 It looks as if the BT cables run very close and parallel to the HV mains
> cable.
>
> Any views ? (I've run out of other ideas).
>
> John Livingston
>

Alec wrote:
> How have you ruled out local RF interference?
>
> What if your cooker oven or a neighbours has a faulty thermostat which
> generates RF interference noise and the mains and phone cables are near to
> each other?
>
> Or it could be related to the street lighting coming on.
>
> Have you been to:
> http://www.dslzoneuk.net/forum/viewforum.php?f=24 and gone to "improve your
> speed."
>
> This procedure if you have not done it will reduce your susceptibility to
> noise pick up.
>
How ?

By use of these -

LF noise - Eddystone 40a noise measuring set (as used by BT and Home
Office).
HF noise - Spectrum analyser and aperiodic loop antenna.

Been there, done that.
I'm a retired RF engineer ....

John

> By use of these -
> LF noise - Eddystone 40a noise measuring set (as used by BT and Home
> Office).
> HF noise - Spectrum analyser and aperiodic loop antenna.
> Been there, done that.
> I'm a retired RF engineer ....

Not really practical for the average non-technical
person.
First step is your modem/routers control panel,
which should give you S/N ratio.
You jot this down at 3-5 min intervals bracketing
the time the problem occurs.
What does a plot of these figures show?
If it is noise pick up you will have a better
idea of how much deterioration in S/N
ratio is occurring, and how near to the
6-7db threshold, when things start to go
pear shaped.

(E-Mail Removed) wrote:
>> By use of these -
> > LF noise - Eddystone 40a noise measuring set (as used by BT and Home
>> Office).
>> HF noise - Spectrum analyser and aperiodic loop antenna.
>> Been there, done that.
>> I'm a retired RF engineer ....
>
> Not really practical for the average non-technical
> person.
> First step is your modem/routers control panel,
> which should give you S/N ratio.
> You jot this down at 3-5 min intervals bracketing
> the time the problem occurs.
> What does a plot of these figures show?
> If it is noise pick up you will have a better
> idea of how much deterioration in S/N
> ratio is occurring, and how near to the
> 6-7db threshold, when things start to go
> pear shaped.

I've got plotted graphs of SNR Margin at 5 second intervals using
Paessler's PRTG plotting software. Router is Draytek 2800, which has
excellent SNMP remote stats and control.

The SNR drops by about 3-6db over a minute, sometimes bottoms at about
6dB, other times causes a resync. It stays at 6-8dB for about 5 min.
with lots of CRC errors, then suddenly clears and jumps back to the
normal 12-13 dB and very few CRC errors. (I've set the router coding
gain and Max down rate to give a stable 2Mb, rather than a more flaky
2.8-3Mb which is the flat out max for the line).

I agree it looks like RF interference - but it's definitely not in my
locality. If it is RFI, it's getting injected into the cable somewhere
between me and the exchange. That's why I was wondering about the
cabinet, since it's near a possible powerful RFI source. It's probably
affecting lots of other people, but maybe they aren't so picky ....

John

John Livingston wrote:
> (E-Mail Removed) wrote:
>>> By use of these -
>> > LF noise - Eddystone 40a noise measuring set (as used by BT and
>> Home
>>> Office).
>>> HF noise - Spectrum analyser and aperiodic loop antenna.
>>> Been there, done that.
>>> I'm a retired RF engineer ....
>>
>> Not really practical for the average non-technical
>> person.
>> First step is your modem/routers control panel,
>> which should give you S/N ratio.
>> You jot this down at 3-5 min intervals bracketing
>> the time the problem occurs.
>> What does a plot of these figures show?
>> If it is noise pick up you will have a better
>> idea of how much deterioration in S/N
>> ratio is occurring, and how near to the
>> 6-7db threshold, when things start to go
>> pear shaped.
>
> I've got plotted graphs of SNR Margin at 5 second intervals using
> Paessler's PRTG plotting software. Router is Draytek 2800, which has
> excellent SNMP remote stats and control.
>
> The SNR drops by about 3-6db over a minute, sometimes bottoms at
> about 6dB, other times causes a resync. It stays at 6-8dB for about
> 5 min. with lots of CRC errors, then suddenly clears and jumps back
> to the normal 12-13 dB and very few CRC errors. (I've set the
> router coding gain and Max down rate to give a stable 2Mb, rather
> than a more flaky 2.8-3Mb which is the flat out max for the line).
>
> I agree it looks like RF interference - but it's definitely not in
> my locality. If it is RFI, it's getting injected into the cable
> somewhere between me and the exchange. That's why I was wondering
> about the cabinet, since it's near a possible powerful RFI source.
> It's probably affecting lots of other people, but maybe they aren't
> so picky ....
> John

You'd be suprised as you could be the only one. Had recent experience
with a SKY Box on a stopped line going broadband & it only caused
problems for one out of 10 users on the same pole & didn't affect
anyone else on the route back to the PCP.

The problem for you, is that ADSL is not a protected service so even
if it is the sub station causing you grieve I very much doubt if
anything will be directly done about it, other than changing some of
your routeing, if at all possible.

kraftee wrote:

>
> You'd be suprised as you could be the only one. Had recent experience
> with a SKY Box on a stopped line going broadband & it only caused
> problems for one out of 10 users on the same pole & didn't affect
> anyone else on the route back to the PCP.
>
> The problem for you, is that ADSL is not a protected service so even
> if it is the sub station causing you grieve I very much doubt if
> anything will be directly done about it, other than changing some of
> your routeing, if at all possible.
>

You're right of course - but its become a bit of an obsession ! The
fault is below the point at which I could reasonably report it, but it's
become a bit of a detective mystery.

I should get out more .....

John

: I've got plotted graphs of SNR Margin at 5 second intervals using
: Paessler's PRTG plotting software. Router is Draytek 2800, which has
: excellent SNMP remote stats and control.
:
: The SNR drops by about 3-6db over a minute, sometimes bottoms at about
: 6dB, other times causes a resync. It stays at 6-8dB for about 5 min.
: with lots of CRC errors, then suddenly clears and jumps back to the
: normal 12-13 dB and very few CRC errors. (I've set the router coding
: gain and Max down rate to give a stable 2Mb, rather than a more flaky
: 2.8-3Mb which is the flat out max for the line).

I have the same router, use Paessler and get the same down rates. You're
scaring me.

I get a stable 2Mbps but my normal SNR is around 4-8dB. Surely you should
be seeing better rates than me?

At 3Mbps the line drops to about 1-2dB, and is extremely unstable.
I blame war.

"John Livingston" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> kraftee wrote:
>
>>
>> You'd be suprised as you could be the only one. Had recent experience
>> with a SKY Box on a stopped line going broadband & it only caused
>> problems for one out of 10 users on the same pole & didn't affect anyone
>> else on the route back to the PCP.
>>
>> The problem for you, is that ADSL is not a protected service so even if
>> it is the sub station causing you grieve I very much doubt if anything
>> will be directly done about it, other than changing some of your
>> routeing, if at all possible.
>
> You're right of course - but its become a bit of an obsession ! The fault
> is below the point at which I could reasonably report it, but it's become
> a bit of a detective mystery.
>
> I should get out more .....
>
> John

It does sound a bit like medium wave RF pickup, the phone line acting as an
aerial, MW signals get stronger as dark approaches, in cyclical 'waves' of a
few minutes. If you are old enough to remember Radio Luxembourg fading
in/out then that's the same thing. Phone lines, especially overhead ones
make a good MW aerial. The balanced pair line in theory helps to reject RF
pickup, but any imbalancing of the line, say by water making contact with
only one half, and RF signal level at your end increases. Placing a MW
radio by your master socket, preferably with a couple of turns of phone line
(pre-any microfilters) wrapped around it, with the router switched off,
might tell you something if the signal gets boosted and fades in/out. Try
it on several very weak stations.

Cork Soaker wrote:
> : I've got plotted graphs of SNR Margin at 5 second intervals using
> : Paessler's PRTG plotting software. Router is Draytek 2800, which has
> : excellent SNMP remote stats and control.
> :
> : The SNR drops by about 3-6db over a minute, sometimes bottoms at about
> : 6dB, other times causes a resync. It stays at 6-8dB for about 5 min.
> : with lots of CRC errors, then suddenly clears and jumps back to the
> : normal 12-13 dB and very few CRC errors. (I've set the router coding
> : gain and Max down rate to give a stable 2Mb, rather than a more flaky
> : 2.8-3Mb which is the flat out max for the line).
>
> I have the same router, use Paessler and get the same down rates. You're
> scaring me.
>
> I get a stable 2Mbps but my normal SNR is around 4-8dB. Surely you should
> be seeing better rates than me?
>
> At 3Mbps the line drops to about 1-2dB, and is extremely unstable.
> I blame war.
>
>

Ah yes - but my loop attenuation is 49.5dB. (3.6Km to exchange) Sounds
like yours is greater than that.
This morning's figures -
SNR Margin 12dB
Down Speed 2176000

Router tweaks (after experimentation to find optimum stability) -
Codinggain 4dB
Maxdnrate 74
Interleaving OFF
Latest firmware update - E.67.2.55

John