SNR on Connection

Tacitus · Nov 30, 2008, 10:11:47

Not iDNet related but could be of general interest.

I've just rebooted my router and on connection it showed the following:

noise margin downstream: 15 db
output power upstream: 11 db
attenuation downstream: 55 db

Within 5 minutes that had dropped to 11dB downstream and it remains around that for the rest of the day unless it gets hit by a sudden noise burst which forces a resync

A BT Speedtest shortly afterwards 09.53am gives the following:

Your DSL connection rate: 2304 kbps(DOWN-STREAM), 448 kbps(UP-STREAM)
IP profile for your line is - 1750 kbps
Actual IP throughput achieved during the test was - 1598 kbps

The profile should probably update to 2000 kps in the next few days. I think 2290 is the trigger point.

Now the question! Why does the snr suddenly drop from 15 to 11dB? Is this simply a noisy line - although at present it's not showing any of the huge errors I sometimes get around morning and teatime'ish.

At present, more often than not it manages to stay up for over 24 hours, occasionally it will manage a whole week!

Rik · Nov 30, 2008, 10:40:49

The drop indicates there was even more noise on the line later than when you rebooted, Tac. At the time the modem negotiates a connection, it will get the best possible speed for its target noise margin and the prevailing noise conditions. After that, fluctuations reflect a change in ambient noise, sometimes giving a higher noise margin, sometimes lower. Some routers are more prone to wild swings, eg Netgear.

Sebby · Nov 30, 2008, 10:43:00

Yep, definitely varying noise is the reason.

Tacitus · Nov 30, 2008, 10:58:30

Quote from: Sebby on Nov 30, 2008, 10:43:00
Yep, definitely varying noise is the reason.

Thanks Seb & Rik. I thought that might be the case, although a quiet line test doesn't show any *obvious* noise. In the past though it always started at 11dB dropping to 6 or so over the day. I'm assured the target snr hasn't been fixed at a higher level, so on the assumption that is true (it came from the script monkeys) it must be the automatic system setting the higher level. It is gradually getting worse though.

I'm on the lookout for a 2Wire at present to see if that makes much difference. I suspect it will, but how much remains to be seen.

Incidentally what does it mean if they are BNIB boxed? Can't quite see the relevance of the Institute for the Blind, if that is the case.

Rik · Nov 30, 2008, 11:03:24

We're not talking about audible noise here, Tac, but RF noise in the MW band. Hence you'll often see me recommending people wander about with a de-tuned radio to search for noise sources.

BNIB - best guess, brand new in box?

Tacitus · Nov 30, 2008, 11:11:06

Quote from: Rik on Nov 30, 2008, 11:03:24
We're not talking about audible noise here, Tac, but RF noise in the MW band. Hence you'll often see me recommending people wander about with a de-tuned radio to search for noise sources.

I really must put my brain in gear..... Given the state of the line I was looking for audible noise. Or even listening for it....

Quote from: Rik on Nov 30, 2008, 11:03:24
BNIB - best guess, brand new in box?

Line I said, bit early yet for putting my brain in gear........

Interesting the MW radio trick as this suggests quite a bit of noise from the modem itself.

Rik · Nov 30, 2008, 11:15:37

Modems radiate some noise, but you're interested in the wiring up to that point more (but also check out the computer's power supply and the monitor).

Tacitus · Nov 30, 2008, 11:28:00

Quote from: Rik on Nov 30, 2008, 11:15:37
Modems radiate some noise, but you're interested in the wiring up to that point more (but also check out the computer's power supply and the monitor).

I've ruled out most things but resiting the modem might be worth a try. Inconvenient, but at least I'll have covered everything.

Rik · Nov 30, 2008, 11:32:13

Always worth a try, though it probably isn't going to solve the problem, unfortunately.

Tacitus · Nov 30, 2008, 11:43:35

Quote from: Rik on Nov 30, 2008, 11:32:13
Always worth a try, though it probably isn't going to solve the problem, unfortunately.

I agree, but I can't say I didn't try.

kinmel · Nov 30, 2008, 12:42:13

SNR is a nightmare for some of us, mine yoyo s about all over the place.

With an Attenuation of 59.4, my present SNR is 8dB, sync'd at 4544 and yet by midnight SNR will be down to about 2dB, fortunately the good old 2700HGV usually manages to hang in there and keep the sync above 4512.

The 2700HGV is certainly worth a try. I would lend you one, but the postage to you and back is about £10 and you can get one to keep from ebay for that.

Edit: On Ebay search for "Business Hub" as well as for "2700HGV"

Rik · Nov 30, 2008, 12:47:26

You're doing better than me, Alan, I'm synced at 3488 on a 57db line.

Glenn · Nov 30, 2008, 12:51:17

Twice the speed of mine, with a similar nm, mines currently 59.9

Rik · Nov 30, 2008, 12:52:30

It makes you want to spit, doesn't it, Glenn.

Glenn · Nov 30, 2008, 12:53:26

I'm resigned to the fact my line won't get quicker.

Glenn · Nov 30, 2008, 12:54:35

I might ask support if they can get BT to reduce the target margin down to 9 from 12 again

Rik · Nov 30, 2008, 12:54:55

Quote from: Glenn on Nov 30, 2008, 12:53:26
I'm resigned to the fact my line won't get quicker.

Me too - no point in worrying about it, my option is to move if I want a better performance.

Rik · Nov 30, 2008, 12:55:16

Quote from: Glenn on Nov 30, 2008, 12:54:35
I might ask support if they can get BT to reduce the target margin down to 9 from 12 again

I have mine pegged at 9, it seems to work best for me.

g7pkf · Nov 30, 2008, 13:08:28

He's not with idnet. (well the original poster)

wonder what support he will get?

mines set to 15

Rik · Nov 30, 2008, 13:10:44

That is high.

Tac will get Demonic support, of course.

Tacitus · Nov 30, 2008, 14:55:42

Quote from: Rik on Nov 30, 2008, 13:10:44
That is high.

Tac will get Demonic support, of course.

Ho ho!!

Are the BT BUSINESS HUB 2700HGV GATEWAY VERSION 2.0 the ones to go for?

Rik · Nov 30, 2008, 14:58:23

They will do nicely.

Tacitus · Nov 30, 2008, 15:28:39

Quote from: Rik on Nov 30, 2008, 14:58:23
They will do nicely.

Good! I'm now the proud owner of the above - or will be when it arrives. £21 - ostensibly brand new so it should be OK.

Expect more pleas for help in setting it up....

Rik · Nov 30, 2008, 15:30:16

Was that with carriage? It seems slightly high...

Glenn · Nov 30, 2008, 15:35:21

Here is all you need to know to get it working http://www.idnetters.co.uk/forums/index.php?topic=8927.0

g7pkf · Nov 30, 2008, 16:31:31

Quote from: Rik on Nov 30, 2008, 13:10:44
That is high.

Lines stable and it drops to 6db at peak train times so in theory i could go down to 12.

but mine is set by the singtel firmware

Sebby · Nov 30, 2008, 18:40:49

Quote from: Rik on Nov 30, 2008, 12:47:26
You're doing better than me, Alan, I'm synced at 3488 on a 57db line.

Indeed - it sounds like a pretty good line, all things considered. I used to get that sync on my 47dB line!

Rik · Nov 30, 2008, 18:42:45

That was this morning, I've had another Sunday burst of noise and I'm now down by 1000k, with a 15db NM on the upstream. Weird.

Tacitus · Nov 30, 2008, 18:45:14

Quote from: Rik on Nov 30, 2008, 15:30:16
Was that with carriage? It seems slightly high...

£16.50 plus £4.50 carriage for a brand new modem isn't outrageous.

Quote from: Glenn on Nov 30, 2008, 15:35:21
Here is all you need to know to get it working http://www.idnetters.co.uk/forums/index.php?topic=8927.0

Thanks for that Glenn. I'll let you know how I get on.

Rik · Nov 30, 2008, 18:46:16

It's not too bad, Tac, and good value even at that price, but they did go through a phase of being much cheaper. Maybe supplies are drying up?

Sebby · Nov 30, 2008, 18:49:08

I've actually got a couple I wouldn't mind getting rid of, Tac. Drop me a PM if you're interested.

Tacitus · Nov 30, 2008, 19:01:44

Quote from: Sebby on Nov 30, 2008, 18:49:08
I've actually got a couple I wouldn't mind getting rid of, Tac. Drop me a PM if you're interested.

Already done the deal thanks Seb

I know I'm prolonging this thread but I thought it might be worth posting some other stats as of 18.55pm:

noise margin upstream: 20 db
output power downstream: 15 db
attenuation upstream: 31 db
tone 0- 31: 00 00 00 04 45 56 66 76 67 77 77 66 66 66 55 00
tone 32- 63: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 64- 95: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 96-127: 00 00 00 67 76 85 77 18 76 67 87 66 66 78 a9 a6
tone 128-159: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
All tones above this are zero.

noise margin downstream: 12 db
output power upstream: 11 db
attenuation downstream: 55 db
tone 0- 31: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 32- 63: 00 00 00 55 67 78 87 08 99 99 99 99 aa aa aa aa
tone 64- 95: 0a 99 99 97 89 99 99 99 99 99 99 99 98 88 77 77
tone 96-127: 76 66 66 67 77 67 76 66 55 66 65 54 34 20 00 00
tone 128-159: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
All tones above this are zero.

I don't know if this gives the more technically minded a clue as to what's going on. Other than the obvious that the line's c..p.

Tacitus · Nov 30, 2008, 19:03:54

Quote from: Rik on Nov 30, 2008, 18:46:16
It's not too bad, Tac, and good value even at that price, but they did go through a phase of being much cheaper. Maybe supplies are drying up?

Could be, as the Business Hubs seem to be quite hard to find. Quite a few of the other sort (single SSID) but they seem to go for £20+, which does seem excessive compared to what I paid.

kinmel · Nov 30, 2008, 19:32:10

Quote from: Tacitus on Nov 30, 2008, 19:03:54
Could be, as the Business Hubs seem to be quite hard to find. Quite a few of the other sort (single SSID) but they seem to go for £20+, which does seem excessive compared to what I paid.

I buy 2700HGVs regularly from Ebay and only ever pay around £10 inc P&P eg this month I bought a BNIB 2700HGV

Tacitus · Nov 30, 2008, 20:14:24

Quote from: kinmel on Nov 30, 2008, 19:32:10

I buy 2700HGVs regularly from Ebay and only ever pay around £10 inc P&P eg this month I bought a BNIB 2700HGV

I think it probably depends who's around at the time you bid. When I looked, there were several going for much the same price as I paid, but I'm not a regular on ebay.

However, I'm satisfied as I don't regard £21 for a brand new modem as expensive. If it doesn't produce better results on my line I can always sell it for no great loss.

kinmel · Nov 30, 2008, 20:21:27

If it sorts the problem then it is a cheap fix

Good luck

Tacitus · Nov 30, 2008, 20:25:08

Quote from: kinmel on Nov 30, 2008, 20:21:27
If it sorts the problem then it is a cheap fix

Good luck

Couldn't agree more and thanks for the good wishes

Sebby · Nov 30, 2008, 21:41:19

Everything is crossed for you!

Rik · Dec 01, 2008, 10:26:49

Except my eyes.

Sebby · Dec 01, 2008, 19:11:18