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Author Topic: Modem-to-wallsocket cables recap (again, groan)  (Read 3449 times)

Weaver

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #15 on: March 26, 2017, 02:08:13 AM »

@burakkucat - I hear you. I didn't know about the solid core thing. And guess what, the Vince cable that I had fell apart. It didn't look anything like the ones in the current product shots.

I will intentionally waste a small amount of money though, in the interests of science only, but I am not optimistic - either about there being anything there to measure, or the possibility of it being measurable given the techniques available, or about the magnitude of any effects rising about the measurement noise floor. I will certainly take a look at those alternative run-it-direct links.

Many thanks to all contributors for valuable insights.
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Weaver

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #16 on: March 26, 2017, 02:25:47 AM »

@Burakkucat - Physics - is the point that my supposed Faraday cage is very imperfect and the shield acts as an aerial? Inside the shield is the gradient of the potential zero? Is it an issue concerning dV/dt inside the shield too?

Skipped most electromagnetism lectures - was too busy fiddling about writing Z80 assembler language at the time til all bourse, and playing games instead of working.
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burakkucat

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #17 on: March 26, 2017, 05:49:58 PM »

Skipped most electromagnetism lectures . . .

It was a very long time ago, I have probably forgotten more than I have remembered.  ::)

Quote
. . . is the point that my supposed Faraday cage is very imperfect and the shield acts as an aerial?

Hmm . . . Or acting as a parasitic omni-directional director. (Whatever that may be.)

Quote
Inside the shield is the gradient of the potential zero? Is it an issue concerning dV/dt inside the shield too?

Bond the screening to a good signal ground and then the screening will behave correctly. Perhaps 7LM could help out with answers to your latest questions?  :-\
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sevenlayermuddle

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #18 on: March 26, 2017, 06:46:53 PM »

Perhaps 7LM could help out with answers to your latest questions?  :-\i

I have a scroll of paper upstairs, from a respected academic institution,  that suggests I once knew about such things.   But that was then and this is now.   After a working life spent (miss spent?) in software development, i would be unable to speak with any confidence.  That is why I generally try to express an opinion, rather than a fact.

Sometimes, believe it or not, I am sometimes even wrong.   That is why I was inviting different views.

Must confess, I have just spent a few moments trying to dig up online technical material, but have found nothing I can cite to justify my suggestion that an ungrounded screen is worse than no screen.  Various posts on various forums, some agreeing and some disagreeing, but nothing really authoritative. :-[

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tubaman

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #19 on: March 27, 2017, 10:39:27 AM »

Hmm, I always thought an ungrounded shield was worse than none at all but I have found quite a few articles that suggest it is not so.
One example is http://www.cablinginstall.com/articles/print/volume-15/issue-7/features/design/the-myths-and-realities-of-shielded-screened-cabling.html.
 :-\
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runitdirect

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #20 on: March 27, 2017, 10:40:07 AM »


The alternative I was thinking about is https://www.run-it-direct.co.uk/rj11-to-rjJ45-patch-leads/RJ11toRJ45patchlead1M/ which is very expensive by comparison and the appearance fails to seduce: not gold-plated, unless they're keeping it a secret, twisted pair but no overall shield, no moulded plugs so less robust-looking and no metal around the plug bodies. I don't see any immediate reason why they might be an improvement, and at a far higher price
The lead you have linked to is not designed explicitly for ADSL/VDSL, they are wired for connecting Panasonic KXT-DA0141 & KXT-DA0142CE DECT Cell stations to structured cabling (4 wires connected). The pins are gold plated like just about every RJ series plug available, we don't make a big deal over that as to be frank it would be marketing drivel but we'll certainly get it added if that is what people are expecting to read! As for shielding, totally & utterly pointless. For a shielded system to work the cable MUST be grounded at both ends. As the incoming line has no ground & there is no grounded shield on ANY filtered faceplate socket this would be impossible to achieve. Indeed almost all modems/routers have no shielding on the DSL input socket either (& if they do that is more to do with internal RFI shielding than grounding the socket). For ADSL/VDSL leads this is what we offer :- https://www.run-it-direct.co.uk/adsl-vdsl-patch-leads/

The VDSL ones use BT CW1724 spec cable which is a two pair cable to CAT5e specifications. We only terminate one pair as that is all that is required. Our customers report improvements when using these cables but obviously like anything involving DSL this can & will vary which is why we do not make any bold claims. Hope this clears things up a little.
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runitdirect

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #21 on: March 27, 2017, 11:12:47 AM »

Hmm, I always thought an ungrounded shield was worse than none at all but I have found quite a few articles that suggest it is not so.
One example is http://www.cablinginstall.com/articles/print/volume-15/issue-7/features/design/the-myths-and-realities-of-shielded-screened-cabling.html.
 :-\
I've only skeeted through that but in our tests shielding did not improve things. Trying to attribute every tiny improvement or impairment down to one thing is quite difficult due to DLM etc. My personal experiences of shielded cable in the network environment (CAT5e/CAT6) was grounding was certainly required in electrically noisy environments like factories (which tended to be the only places where shielded systems were specified).
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nallar

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #22 on: March 27, 2017, 01:18:29 PM »

For a shielded system to work the cable MUST be grounded at both ends.

Grounding on both ends can cause ground loops - especially for structured cabling connecting between rooms which will be on different circuits. It's usually okay for patch cables as the cables are going to be terminated on both ends in devices which are on the same circuit.
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Weaver

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #23 on: March 27, 2017, 01:39:41 PM »

I've ordered some of these
    https://www.run-it-direct.co.uk/adsl-vdsl-patch-leads/adslvdslcat5patchlead025m/
in a mixture of different lengths. It's good that run-it-direct do really short cables. Thanks to ejs for that tip.

I will try my very best to do the right thing statistically when comparison testing. It will be Tandy vs Vince vs run-it-direct. I certainly won't be surprised by a null result. Ideas:
  • This procedure (at a minimum) will be used in order to keep DLM at bay:
        http://forum.kitz.co.uk/index.php/topic,15905.msg295891.html
  • Cables will only be switched over while modems are powered down.
  • I have also thought about always rebooting a modem several times after switching cables and having two presentations, one with the first result immediately after the cable switch-over excluded and one with it included. A minimum of three measurements after each swap would give a measurement of the noise in the results and excluding the first one would be interesting.
Does anyone have any suggestions to improve my chances of getting anything meaningful out of it? (Slim though they may be.)
« Last Edit: March 27, 2017, 01:50:17 PM by Weaver »
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Chrysalis

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #24 on: March 27, 2017, 01:40:10 PM »

Just a few comments --
  • I fail to understand how a screened cable with metallised plugs on its ends can be superior to other cables if the screening is not connected to a good signal earth.
  • As much as I like Vince (Mr Telephone Supplies), I disagree with his policy of attempting to make patch cables out of the solid core cable used for structured wiring. Structured wiring -- solid core. Patch cables -- stranded core. As other have discovered, the plugs crimped onto the solid core wires of Vince's patch cables will come off, sooner or later.
  • As ejs has mentioned, Run IT Direct now have a different set of patch cables available. (8P4C modular plug and 6P4C modular plug, respectively, at opposite ends.) I would be tempted to use one of those cables.

burakkucat could you be kind enough to link to what you consider the highest quality short cable on run it direct?

I noticed they have a paragraph stating cat5e is best quality for a patch cable yet the cat5e cables are the cheapest which makes it confusing.

is this one provided by ejs the best quality https://www.run-it-direct.co.uk/adsl-vdsl-patch-leads/adslvdslcat5patchlead1m/ ?

Thanks
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runitdirect

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #25 on: March 27, 2017, 01:41:57 PM »

Grounding on both ends can cause ground loops - especially for structured cabling connecting between rooms which will be on different circuits. It's usually okay for patch cables as the cables are going to be terminated on both ends in devices which are on the same circuit.
Different circuits shouldn't make any difference they should all be connected to the same earth connection at the DB (as would the patch cabinet at one end & the equipment at the other).
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runitdirect

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #26 on: March 27, 2017, 01:53:17 PM »

burakkucat could you be kind enough to link to what you consider the highest quality short cable on run it direct?

I noticed they have a paragraph stating cat5e is best quality for a patch cable yet the cat5e cables are the cheapest which makes it confusing.

is this one provided by ejs the best quality https://www.run-it-direct.co.uk/adsl-vdsl-patch-leads/adslvdslcat5patchlead1m/ ?

Thanks
Which leads are you comparing?
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Weaver

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #27 on: March 27, 2017, 02:02:17 PM »

@chrysalis - I think ejs and Burakkucat Both linked to the exact same one that I ordered. I've ordered several 0.25m, 0.5m and 1m, and I'll see what I can get away with in terms of keeping them all as short as poss. If I can get away with the 0.25m ones then so much the better. I am using two 0.5m cables currently but found it a bit uncomfortable reaching the third wallsocket, so currently I have one 1m.
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nallar

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #28 on: March 27, 2017, 03:35:55 PM »

Different circuits shouldn't make any difference they should all be connected to the same earth connection at the DB (as would the patch cabinet at one end & the equipment at the other).

I'd been taught that this causes the shielding to become a parallel path for ground current to flow, inducing common mode noise on the cable inside the shield.

That is correct but not actually significant and it should be bonded at both ends. Sorry for the misinformation.

Some references supporting your statement that they should be bonded at both ends:

http://www.compliance-club.com/archive/old_archive/020514.htm
http://www.siemon.co.uk/us/standards/Screened_and_Shielded_Q_and_A.asp
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Weaver

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Re: Modem-to-wallsocket cables recap (again, groan)
« Reply #29 on: March 27, 2017, 04:57:35 PM »

Did that article referred to earlier
    http://www.cablinginstall.com/articles/print/volume-15/issue-7/features/design/the-myths-and-realities-of-shielded-screened-cabling.html
say that even an unearthed screen is a good thing, by 20dB ?
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