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Standard User coreswitch
(newbie) Thu 31-Jan-13 23:17:48
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Slow line speed, high SNR, strange device on line


[link to this post]
 
At a friends whos approx. 1 mile from mine. I get just under 7 meg, whilst his TalkTalk echolife box only manages ~1.6meg.

The SNR is quite high. The house is from the 60's/70's and probably has the original line installed from way back when.

If anyone can shed some light on what this mystery junction box is it would be greatly appreciated. The line enters at the bottom pair of screws, runs through a knife-switch style arrangement and exits at the top on its way to an NTE5. The center top screw is what I believe is a ground wire, which at somepoint has been cut.

http://img705.imageshack.us/img705/852/imag0883m.jpg

And, for anyone who may be interested, a screenshot of the routers ADSL status page

http://img820.imageshack.us/img820/1415/echolifeadsl...

Many thanks
Administrator MrSaffron
(staff) Thu 31-Jan-13 23:32:26
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Re: Slow line speed, high SNR, strange device on line


[re: coreswitch] [link to this post]
 
External black wire enters at bottom and white to the NTE5, what is the pair of wires to the left of this going to? Looks like bell/speaker wire to me.

The attenuation is about right for the sync speed, so this socket must be having a massive effect on the attenuation or the the line is around 25 dB longer than yours. Not impossible given physical distance and wiring routes can be complex

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User coreswitch
(newbie) Thu 31-Jan-13 23:35:17
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Re: Slow line speed, high SNR, strange device on line


[re: MrSaffron] [link to this post]
 
Ive never seen one of these before, I just wondered what the hell it is. Doesnt look like a passive junction box to me

[EDIT] The wire that exits left at the top? Its a bare copper wire, looks like it might have been an earth at some point but it runs up the roof truss and then has been chopped.

Edited by coreswitch (Thu 31-Jan-13 23:37:04)


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Standard User micksharpe
(eat-sleep-adslguide) Fri 01-Feb-13 00:15:27
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Re: Slow line speed, high SNR, strange device on line


[re: coreswitch] [link to this post]
 
It's an old GPO junction/protector box. Overhead phone lines, perchance? At least, in the past?

'Sir, please,' she said ... 'Will you not share your wisdom with us?'
'I have no wisdom,' he told her.
'Your experiences, then?'
'They have been trivial, uninteresting, and full of error.'
Ian M. Banks - Feersum Endjinn
.
It Ought to be Easy | Greasemonkey scripts

Edited by micksharpe (Fri 01-Feb-13 00:16:31)

Standard User yarwell
(sensei) Fri 01-Feb-13 09:08:08
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Re: Slow line speed, high SNR, strange device on line


[re: coreswitch] [link to this post]
 
the downstream attenuation is very high at 70 dB. Seems contrary that the noise margin is high with 13 dB - is it the same after a reboot ? On the other hand the reported downstream power is 0 which may be messing things up on the stats.

--

Phil

MaxDSL - goes as fast as it can and doesn't read the line checker first.

MaxDSL diagnostics
Administrator MrSaffron
(staff) Fri 01-Feb-13 09:58:41
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Re: Slow line speed, high SNR, strange device on line


[re: micksharpe] [link to this post]
 
Makes sense seeing a better picture, the long metal bits are sacrifical in the event of a lightning strike

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Administrator MrSaffron
(staff) Fri 01-Feb-13 10:01:01
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Re: Slow line speed, high SNR, strange device on line


[re: coreswitch] [link to this post]
 
If you have a modern NTE5a with lightning arrestor then replacing this junction box with a more modern one e.g.

http://www.telephone-wiring.co.uk/bt-77a-telephone-j...
(Link for picture, not recommendation of source)

or at least removing what is now a nice big aerial would be a good idea (the copper wire)

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User systemx
(experienced) Fri 01-Feb-13 11:48:53
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Re: Slow line speed, high SNR, strange device on line


[re: MrSaffron] [link to this post]
 
In reply to a post by MrSaffron:
Makes sense seeing a better picture, the long metal bits are sacrifical in the event of a lightning strike


They are not. Originally they had two fuses fitted, but they offered little protection and caused a lot of call outs to replace them.

The bars were fitted later and offer no protection. Overvolt protection is provided by two removable resistors between the line and earth, hence the earth connection.

These days it should be removed and replaced with a NTE-5 as the resistors may well have a detrimental effect on BB.
Administrator MrSaffron
(staff) Fri 01-Feb-13 12:07:31
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Re: Slow line speed, high SNR, strange device on line


[re: systemx] [link to this post]
 
Thanks for the update.

Had assumed it was low melting point wire.

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User eckiedoo
(regular) Fri 01-Feb-13 20:47:11
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Re: Slow line speed, high SNR, strange device on line


[re: systemx] [link to this post]
 
From Telecomms Principles 1, 2 & 3 in the 1950s, I recollect that the GPO Telephones Lightning Protectors then were two blocks of carbon with chamfered edges, and varnished.

I think a block was connected to each line and the two blocks were placed in physical contact with the varnish acting normally as an insulator, breaking down when lightning struck; and supposedly protecting the equipment.

These are possibly the items you describe as "Overvolt protection is provided by two removable resistors between the line and earth, hence the earth connection.".

As I never worked for any telephone company/organisation, I have not encountered any in practice.

Possibly a former GPO Telephone Boy could enlighten us.
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