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[GigabitEthernet]

I have quite a lot of interference here and I will try anything to reduce it!

I have read a few posts about 'earthing' an ADSL cable (if I am correct?). How would I go about doing this? Would I gain any benefit?

[roseway]

Probably not. Assuming that your present cable is good quality twisted-pair, then it will only pick up very small amounts of interference. So if you get 'quite a lot' of interference, then it's being picked up somewhere else.

The ADSL signal is balanced (i.e. neither side is earthed), so any earthing would only apply to a screen, and an unearthed screen will still act as a Faraday cage and reject interference.

[JGO]

I assume you have interupted the bell wire in some way so the twin cable is properly balanced.

The only way earthing could help would be to connect via screened twin cable and earth the screening. This is not a technique I've ever met and you can't do that on BT's VDSL or ADSL cable outside the premises anyway which could well be where the interference is picked up.

Frankly the problem is trying to use a low frequency (telephone) techniques across the transition  to High/Radio frequencies, where one should use unbalanced coax cable.

There is an additional point. Extensions, i.e. spurs off the internal wiring, don't have any effect on telephone frequencies, but if much longer than about 17 m they can clobber the RADIO bandwidth and reduce speed. There is a cure, a filtered faceplate  at the master socket so the broadband doesn't "see" the extension - a micro filter at the extension end isn't the same.

Roll on FFTP !

[sheddyian]

You can get screened RJ11 cables (ADSL Nation do one) that's have metal RJ11 plugs and an outer screen around the twisted pairs.  However, you need to have RJ11 sockets on your equipment that have a metal outer (most are plastic) or this screen will just be floating, not connected to anything.

I tried one a while back.  Admittedly I wasn't experiencing any interference problems at the time, but I couldn't see any improvement between the screened cable and a cheap flat RJ11 cable with 2 untwisted wires, 1 metre in length.

I also tried grounding the unused twisted pairs in the longer run cable to my ADSL phone socket, and connected this to the actual earth outside.  Again, I couldn't detect any improvement.

But if you've got interference problems, an interest and a bit of time (and money) to spend, it might be interesting to play about.

But RF interference will also affect your phone line on the way from the exchange to the house (where you can't do anything about it) and also your lan wiring might well transfer interference they pick up into the modem as well. 

Just my thoughts on the matter

Ian

[GigabitEthernet]

I also tried grounding the unused twisted pairs in the longer run cable to my ADSL phone socket, and connected this to the actual earth outside.  Again, I couldn't detect any improvement.

I might try that. Would you mind elaborating a bit more?

[sheddyian]

Some time back, I'd replaced the cheap untwisted telephone extension cable with CAT5 network cable.

This cable ran from the master socket to some extensions, into one of which was plugged the ADSL modem.

Replacing the cheap phone cabling with CAT5 cabling did give me an improved synch speed.

I wired pins 2 and 5 of the phone sockets to one of the pairs in the CAT 5 cable.

I later wondered if I could improve it further.  As I was only using 1 of the pairs in the cable, I soldered the other pairs all together at both ends of the cable run.  Then at the master socket end, I connected this soldered pairs to one wire, which I ran out of the window and connected to an electrical earth rod that I'd hammered into the ground.

Although the CAT 5 cable wasn't screened, I felt that having the spare pairs grounded might act as an improvised screen, at no cost and not too much effort.

But, with before & after tests on synch speed and attenuation, I couldn't detect any difference.

It may have helped the long term error seconds, but at the time I wasn't monitoring those as they weren't excessive and they didn't give me any real problems.

I've since eliminated the extension wiring, the modem is now plugged into an ADSL Nation filtered faceplate on the NTE5 master socket immediately where the phone line comes in the house.

Ian

[burakkucat]

I sat and stared (and stared) until the thread, so referenced, was found. 

I had quite forgotten just how much 'tinkering' takes place in Sheddy-land. 

[sheddyian]

I'd intended to link to that thread, but I forgot!

So, here's a link to the rambling thread of me earthing the spare pairs in the CAT5 cabling I was using for telephony and ADSL

http://forum.kitz.co.uk/index.php/topic,11373.0.html

Which itself spawned another thread about running a modem off a nicad battery to eliminate mains interference !

Ian

[JGO]

Sheddyian, I'm curious what the cable you mention is like.

 I've calculated the skin depth in copper at 1MHz (somewhere in the information band) as 0.033 mm. To behave as true screen i.e. with good isolation between currents inside and on the outside of the sheathing, I would have thought you needed some 5 skin depths i.e. 0.16 mm and about 0.275 at 600 kHz. This is NOT common or cable,  and sounds costly. I've seen that thickness on 1 inch high power coax but doubt if that is the sort of thing you mean !

[sheddyian]

Sheddyian, I'm curious what the cable you mention is like.

If you're interested in the CAT5 cable I used for telephone & ADSL, it was standard CAT5 (not even CAT5e) twisted pair cable, from an old patch cable.  Most modern patch cables are stranded (to make them more flexible), this was solid cores even though it was a patch cable.  Was probably from mid - late 1990's.  I cut the plugs off both ends

What else can I say about it?  It seemed of typical thickness, but I didn't measure the cores.  As it was quite old and marked to CAT5 standard I assume it was real copper rather than these cheap fake cables that have appeared more recently.

And it didn't have any form of outer screening, it was just unshielded twisted pair with 4 pairs - standard CAT5 stuff.

The solid cores allowed me to punch it into the IDC terminals on the telephone sockets without difficulty - thats why I chose this particular cable.

Ian

[JGO]

" You can get screened RJ11 cables (ADSL Nation do one) that's have metal RJ11 plugs and an outer screen around the twisted pairs.  However, you need to have RJ11 sockets on your equipment that have a metal outer (most are plastic) or this screen will just be floating, not connected to anything."

On re reading carefully you havent seen the one I'm refering to .

I'm a wee bit suspicious of any special cables - maybe you have heard of the Hi Fi speaker cables solid silver ?  I'm not saying they don't work at all, but is the improvement worth the extra cost  and where does it come from ?
 

[sheddyian]

I picked the wrong cable to describe!

My testing on my setup showed that the ADSL nation screened RJ11 cable didn't make any improvement, in fact it gave me a slightly lower S/N margin than the cheap single pair RJ11 cable.  This measurement was repeatable between cable swaps and reboots, so wasn't a chance reading.

The ADSL Nation cable has an outer foil screen, I'm not sure if the pairs themselves are individiually screened.  The screen is connected to the metal screening on the RJ11 plugs.

It's well made, I'll give it that!

I suppose, given that it's twisted pair, it might provide some improvement against noise for someone who currently has a long (maybe 10 - 15 metre?) run of the flat untwisted RJ11 modem cables that you can buy?

Agree with you on the hifi speaker cable thing

edit to add :

When I was comparing the screened cable with unscreened flat untwisted, the main difference that I detected was radiated ADSL noise - using a MW radio, I could detect the ADSL hiss at a distance of 30 - 50 cm with the unscreened cable, but when using screened RJ11 interconnect I had to hold the radio around 10cm or nearer to receive the same volume of ADSL hiss.

As an aside, when I was wandering around with my radio the other week trying to locate the source of interference that was causing resynchs, I noticed that when I stood on top of the rectangular GPO "manhole", I could hear the ADSL hissing away

Ian

ps what's the modern term for "manhole"?  I use it here because everyone will know what I mean, but I accept there are women engineers too.  "Access chamber" doesn't sound right!

[c6em]

Good pdf on the merits of FTP Cat5e over UTP  Cat5e (foil shielded vs unshielded)

http://www.gocsc.com/UserFiles/File/Siemon/WPShieldedMythCUS.pdf

[sheddyian]

Good pdf on the merits of FTP Cat5e over UTP  Cat5e (foil shielded vs unshielded)

http://www.gocsc.com/UserFiles/File/Siemon/WPShieldedMythCUS.pdf

Thanks for that, will give it a good read later (maybe in my shed!)

Ian

[burakkucat]

ps what's the modern term for "manhole"?  I use it here because everyone will know what I mean, but I accept there are women engineers too.  "Access chamber" doesn't sound right!

Until such time as Black Sheep utters the correct phrases, I shall make mention of Joint Box, Footway (JBF) and Joint Box, Carriageway (JBC).