Is this noise margin variation normal?

Sample from RouterStats log.

Sun 06 Dec 2009 09:09:48, Noise Margin= 12.0, Sync Speed= 6368, 1 day, 0:46:00

Sun 06 Dec 2009 19:30:13, Noise Margin= 3.5, Sync Speed= 6368, 1 day, 11:06:23

Router ST585 v 6.2.17.5. d/s attenuation 40dB. Remained synced all day.

No; a margin variation of 8.5dB (at the same sync speed) is not normal.

Have you tried the usual tricks (removing the ring wire, connecting the router into the 'test' socket, etc.)?

Yes it is.

Why do you think that the noise margin should not vary?

In reply to a post by adebov:

No; a margin variation of 8.5dB (at the same sync speed) is not normal.

Have you tried the usual tricks (removing the ring wire, connecting the router into the 'test' socket, etc.)?

Filter faceplate at master socket, connected to router 6 feet away.

BTW stats this morning

Mon 07 Dec 2009 08:14:19, Noise Margin= 11.0, Sync Speed= 6368, 1 day, 23:50:28

Yes, it is normal. Once it goes dark numerous factors come into play and the background noise will increase. It can be anything from 3dB to 15 dB (or maybe even more).

If you resync now with a lower margin, this evening it will loose sync and reconnect at a lower speed again. Just leave as is.

If you could stop the rotation of the earth and orbiting around the sun then you could stabilise the margin.

In reply to a post by MHC:

If you could stop the rotation of the earth and orbiting around the sun then you could stabilise the margin.

I'll work on it

Actually, I am amazed it stays synced at such a low margin!

If SNR Margin is used correctly it should stay sync'd at 0dB. But who knows with router manufacturers?

A router should sync at a specified SNR which is rarely stated - the MARGIN is the spare available.

OK thanks.

btw: now have a G1, a GF1, 14-45, 45-200 and 20mm f/1.7 pancake

In reply to a post by MHC:

Yes, it is normal. Once it goes dark numerous factors come into play and the background noise will increase. It can be anything from 3dB to 15 dB (or maybe even more).

If you resync now with a lower margin, this evening it will loose sync and reconnect at a lower speed again. Just leave as is.

If you could stop the rotation of the earth and orbiting around the sun then you could stabilise the margin.

Variations of more than 6dB usually indicate a split pair, or bad wiring on the customer's side of the master socket.

At >6Mb a split pair is unlikely.

Mine can vary by up to 12dB - and that is irrespective of wiring and I know of others where it can be as low as 1 dB variation.

Variations of more than 6dB usually indicate a split pair

What's a split pair?

When one wire from the orange pair is used, and one from the blue pair.

Rather than the two wires from the same twisted pair. Probably a very common issue particularly on new builds.

Thanks Andrew. I assume that error, if it exists, could occur anywhere between the exchange and my master socket?

It could but would be a mistake in the wiring by BT (note the external BT side wiring usually has different colour cores to it, than the internal stuff).

Well, most of my line is underground but the last 400 yards is overhead and I know for a fact that there are 5 junction boxes in that stretch due to numerous breaks over the years! Could be in one of those

If this split pair exists, would it affect the downstream attenuation? I am straight line 2.3km from exchange with 40dB attenuation.

Nope

Roger!!

I knew it couldn't last

Mon 07 Dec 2009 16:59:09, Noise Margin= 4.5, Sync Speed= 6368, 2 days, 8:35:17

Mon 07 Dec 2009 16:59:24, Noise Margin= -8.0, Sync Speed= 6368, 2 days, 8:35:32

Mon 07 Dec 2009 16:59:54, Noise Margin= 12.5, Sync Speed= 4672, 0 days, 0:00:13

In reply to a post by Andrew_W:

Well, most of my line is underground but the last 400 yards is overhead and I know for a fact that there are 5 junction boxes in that stretch due to numerous breaks over the years! Could be in one of those

If this split pair exists, would it affect the downstream attenuation? I am straight line 2.3km from exchange with 40dB attenuation.

Is the last 400 yards in the street, or is it over your property ?

I inderstand that BT will re-lay the cable for free, if you dig and supply the duct.

In reply to a post by zebedeee:

Is the last 400 yards in the street, or is it over your property ?

I inderstand that BT will re-lay the cable for free, if you dig and supply the duct.

It's over my property. I dug a trench 200 yards long some years ago to carry a water pipe and can still feel the pain Think I would rather put up with the n/m variations!! Nice thought though