Sudden fall and rise in SNR

Having had a recent 'episode' with ADSL on my line I have been watching SNR
more than I have in the past.

I find someone turns something on and I get an instant SNR drop of about
1.5db (maybe 8 to 6.5) when they turn it off I get an instant rise of
1.5db.

They might turn 'it' on at 6pm then off again at 10 or 11, seen it on early
in the morning once, also seen it on Friday afternoon (half day?).

It isn't anything in this (detached) house. I have a bit of reasonable
twisted pair between a BT faceplate/filter on the master socket and the
ADSL modem so I can't really see it being radio frequency pick up.

Looks like it is injecting noise possibly into the mains or into a phone
line where it couples to other lines in the bundle.

Anyone else seen anything like this, I don't think I have seen anyone
talking about anything similar. Seems whatever 'it' is it must be pretty
faulty and I suppose it is probably near my end but could be anywhere
between me and the exchange.
--

In message <(E-Mail Removed)>, nospam
<(E-Mail Removed)> writes
>
>Having had a recent 'episode' with ADSL on my line I have been watching SNR
>more than I have in the past.
>
>I find someone turns something on and I get an instant SNR drop of about
>1.5db (maybe 8 to 6.5) when they turn it off I get an instant rise of
>1.5db.
>
>They might turn 'it' on at 6pm then off again at 10 or 11, seen it on early
>in the morning once, also seen it on Friday afternoon (half day?).
>
>It isn't anything in this (detached) house. I have a bit of reasonable
>twisted pair between a BT faceplate/filter on the master socket and the
>ADSL modem so I can't really see it being radio frequency pick up.
>
>Looks like it is injecting noise possibly into the mains or into a phone
>line where it couples to other lines in the bundle.
>
>Anyone else seen anything like this, I don't think I have seen anyone
>talking about anything similar. Seems whatever 'it' is it must be pretty
>faulty and I suppose it is probably near my end but could be anywhere
>between me and the exchange.

Yes I see a similar reproducible effect, but not as large (my drop is
about 1dB). My SNR drops at about 7:45am and goes up again at about
6:15pm, five days/week, Saturdays sometimes look like weekdays,
sometimes it rises again about 1:00pm (half day!). Sundays can be
nothing, an hour or two or most of the day - but it usually starts
later. The times vary a bit (minutes) each day.

Best I can pin it down to is lighting in an agricultural machinery
workshop about 400m down the road. Its something that gets switched on
when the first person arrives to start work and is switched off when the
last person leaves at night. Talking to the boss the times are roughly
right for their start/stop (they work 8am - 6pm).

It is not a problem for me, because it drops during the day (when SNR is
high anyway) and rises again as it gets dark when the SNR drops off
because (I presume) of pickup of radio broadcasts (all the wiring from
here to the exchange (3km+) is overhead).

If I reboot the router during the day I get 7400-7600 sync speeds with
low/zero error rates (even when they are at work), however at those
speeds come 9 or 10 in the evening (after they have gone home) the error
rate on the line makes it unusable - so I reboot and get 6300-6400 at
which speed the line is much more usable.

I see a really repeatable daylight/dark cycle of SNR. Daylight is 8-9dB.
Dark is 5dB.

Regards
--
Peter R Cook

nospam wrote:
> Having had a recent 'episode' with ADSL on my line I have been watching SNR
> more than I have in the past.
>
> I find someone turns something on and I get an instant SNR drop of about
> 1.5db (maybe 8 to 6.5) when they turn it off I get an instant rise of
> 1.5db.
>
> They might turn 'it' on at 6pm then off again at 10 or 11, seen it on early
> in the morning once, also seen it on Friday afternoon (half day?).
>
> It isn't anything in this (detached) house. I have a bit of reasonable
> twisted pair between a BT faceplate/filter on the master socket and the
> ADSL modem so I can't really see it being radio frequency pick up.
>

then try a different pair of glasses. You have kilometers of unshielded
twisted pair between you and the exchange, and the dominant noise on
your line will normally be MW RF picked up on that.


> Looks like it is injecting noise possibly into the mains or into a phone
> line where it couples to other lines in the bundle.
>
> Anyone else seen anything like this, I don't think I have seen anyone
> talking about anything similar. Seems whatever 'it' is it must be pretty
> faulty and I suppose it is probably near my end but could be anywhere
> between me and the exchange.

Sorry to disappoint you, but its completely normal and not in anyway a
fault that you can lay at your ISP's door, or BT.

They are not responisble for the thousands of millions of bits of
equipment in use all over the country that may or may not generate
interference.

You can try putting a suppressor plug on the modem, and that might cut
down any mains borne noise.

If its reliably repeatable, OFCOM might have something to say though.

someone else reported something similar however..central heating boiler
was surmised.

Try getting your ISP to fix that...;-)

Invalid <(E-Mail Removed)> wrote:

>>Anyone else seen anything like this, I don't think I have seen anyone
>>talking about anything similar. Seems whatever 'it' is it must be pretty
>>faulty and I suppose it is probably near my end but could be anywhere
>>between me and the exchange.
>
>Yes I see a similar reproducible effect, but not as large (my drop is
>about 1dB). My SNR drops at about 7:45am and goes up again at about
>6:15pm, five days/week, Saturdays sometimes look like weekdays,
>sometimes it rises again about 1:00pm (half day!). Sundays can be
>nothing, an hour or two or most of the day - but it usually starts
>later. The times vary a bit (minutes) each day.
>
>Best I can pin it down to is lighting in an agricultural machinery
>workshop about 400m down the road. Its something that gets switched on
>when the first person arrives to start work and is switched off when the
>last person leaves at night. Talking to the boss the times are roughly
>right for their start/stop (they work 8am - 6pm).
>
>It is not a problem for me, because it drops during the day (when SNR is
>high anyway) and rises again as it gets dark when the SNR drops off
>because (I presume) of pickup of radio broadcasts (all the wiring from
>here to the exchange (3km+) is overhead).

That's interesting, my 'timing' looks more like domestic usage, maybe an
ADSL or POTS modem they don't keep always on. I can't believe so much SNR
loss from crosstalk between lines is normal. There must be loads of ADSL
going down the same cable. I can 'see' about 20 wireless networks from
here.

>I see a really repeatable daylight/dark cycle of SNR. Daylight is 8-9dB.
>Dark is 5dB.

My line is all underground and I see about 1.5db variation over the daily
cycle. I can keep 8128 sync though it, the extra 1.5db loss increases the
error rate a bit in the evenings. If I ever get ADSL2+ I'm sure it would
knock out a lump of bandwidth. Just a bit annoying.

--

Brian Gregory [UK] wrote:
> "nospam" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>> Having had a recent 'episode' with ADSL on my line I have been watching
>> SNR
>> more than I have in the past.
>>
>> I find someone turns something on and I get an instant SNR drop of about
>> 1.5db (maybe 8 to 6.5) when they turn it off I get an instant rise of
>> 1.5db.
>>
>> They might turn 'it' on at 6pm then off again at 10 or 11, seen it on
>> early
>> in the morning once, also seen it on Friday afternoon (half day?).
>>
>> It isn't anything in this (detached) house. I have a bit of reasonable
>> twisted pair between a BT faceplate/filter on the master socket and the
>> ADSL modem so I can't really see it being radio frequency pick up.
>>
>> Looks like it is injecting noise possibly into the mains or into a phone
>> line where it couples to other lines in the bundle.
>>
>> Anyone else seen anything like this, I don't think I have seen anyone
>> talking about anything similar. Seems whatever 'it' is it must be pretty
>> faulty and I suppose it is probably near my end but could be anywhere
>> between me and the exchange.
>
> 1.5dB is nothing.
>
> My S/N margin drops by 6dB at night when the night time ionosphere brings in
> numerous European medium wave broadcasts. And this is on a line that
> underground all the way to the exchange.
>
Coo. That must be long. I only get about 3dB...

Invalid wrote:
> In message <(E-Mail Removed)>, nospam
> <(E-Mail Removed)> writes
>>
>> Having had a recent 'episode' with ADSL on my line I have been
>> watching SNR
>> more than I have in the past.
>>
>> I find someone turns something on and I get an instant SNR drop of about
>> 1.5db (maybe 8 to 6.5) when they turn it off I get an instant rise of
>> 1.5db.
>>
>> They might turn 'it' on at 6pm then off again at 10 or 11, seen it on
>> early
>> in the morning once, also seen it on Friday afternoon (half day?).
>>
>> It isn't anything in this (detached) house. I have a bit of reasonable
>> twisted pair between a BT faceplate/filter on the master socket and the
>> ADSL modem so I can't really see it being radio frequency pick up.
>>
>> Looks like it is injecting noise possibly into the mains or into a phone
>> line where it couples to other lines in the bundle.
>>
>> Anyone else seen anything like this, I don't think I have seen anyone
>> talking about anything similar. Seems whatever 'it' is it must be pretty
>> faulty and I suppose it is probably near my end but could be anywhere
>> between me and the exchange.
>
> Yes I see a similar reproducible effect, but not as large (my drop is
> about 1dB). My SNR drops at about 7:45am and goes up again at about
> 6:15pm, five days/week, Saturdays sometimes look like weekdays,
> sometimes it rises again about 1:00pm (half day!). Sundays can be
> nothing, an hour or two or most of the day - but it usually starts
> later. The times vary a bit (minutes) each day.
>
> Best I can pin it down to is lighting in an agricultural machinery
> workshop about 400m down the road. Its something that gets switched on
> when the first person arrives to start work and is switched off when the
> last person leaves at night. Talking to the boss the times are roughly
> right for their start/stop (they work 8am - 6pm).
>
> It is not a problem for me, because it drops during the day (when SNR is
> high anyway) and rises again as it gets dark when the SNR drops off
> because (I presume) of pickup of radio broadcasts (all the wiring from
> here to the exchange (3km+) is overhead).
>
> If I reboot the router during the day I get 7400-7600 sync speeds with
> low/zero error rates (even when they are at work), however at those
> speeds come 9 or 10 in the evening (after they have gone home) the error
> rate on the line makes it unusable - so I reboot and get 6300-6400 at
> which speed the line is much more usable.
>
> I see a really repeatable daylight/dark cycle of SNR. Daylight is 8-9dB.
> Dark is 5dB.

yeah. Ive been at 6dB all day. Its down to 5dB now.

And synching at exactly 4000kbps. Never been on that exact frequency
before....its been

>
> Regards

If anyone is interested here is a 24hour plot of what I experience.

http://img392.imageshack.us/img392/2...r121008cy4.jpg

The top trace is SNR in db (@8128 sync) the red trace is receive errors per
second the scale for which is 2.5x the SNR db scale, 2840 errors in the
period.

--