shielded/earthed Cat 5 8P8C "RJ45" pattress box

[SparkyTris]

Please could anyone recomend a good, screened (and preferably earthable) surface mounting solution for terminating foil-screened Cat5 cable with an 8P8C socket?

ideally the back-box and faceplate will be screened with an earth terminal.

Ive just installed a laptop, about 80m of FTP cat5, a PoE injector inside a modern tin-can type building, connected to a 5Ghz wifi radio on the outside of the building, and the freeview TV service is experiencing degraded SNR whenever the laptop or the (powered-up) radio are connected to the ends of the cat5.

my initial hypothesis is baseband (ethernet, not 5Ghz - TV SNR drops even when radio is off but laptop is on) noise from the ethernet ports of the the radio and/or laptop getting onto and radiating from the foil screen of the cable.
(I am not ruling out a crappy TV installation but "it worked fine before I put up the dish"....)

at present the FTP cat 5 is terminated with apparently unscreened (and certainly unearthed) plastic pattress boxes.

I am using metal screened 8P8C "RJ45" male connectors throughout.

 

[Robin0577]

I've not seen screened plastic surface boxes (that's not to say they don't exist)

It may be that you need to go with a metal surface box such as this http://www.tlc-direct.co.uk/Products/MKK2213.html and a metal face plate.

Or if you have a plastic box with an earth terminal, you could try conductive nickel screening paint on the inside - http://cpc.farnell.com/electrolube/.../dp/SA02327?in_merch=Products From This Range

 

[endecotp]

Are your metal male connectors plugged into metal female sockets on these wall boxes?

My recollection is that shielded twisted pair works best if the shield is connected to earth only at one end; presumably your PoE injector is doing that. So just make sure that the screen is continuous, i.e. that your screened metal plugs are connecting to screened sockets. Screened keystone punch-down sockets are apparently available, though I've never seen one in person; google for "shielded keystone punch down".

Can you test with ethernet but without PoE? What if laptop is not connected to mains?

 

[SimonH2]

It's unusual to get that sort of interference - ethernet is quite well balanced if connected properly.

Sort of answering your question, there are certainly shielded connectors. This panel is one I did for a customer a few years ago, and the sparky for some reason decided screened cable would be a good idea - so I used shielded connectors at the patch panel end so as to earth the screen (nothing else has screened cables or sockets). The first picture is the main batch of cables part terminated, the second is a rear view and you can see some later added cables (unscreened) terminated with unscreened connectors.

Untitled

• SimonH2
• 13 Feb 2011
• 4

Untitled

• SimonH2
• 13 Feb 2011
• 4

I would double check the data cabling and make sure you don't have any bad joints or split pairs*. If you get noise without the radio powered up, then you've got a distinctly dodgy ethernet link !

* Split pairs occur when you have a balanced circuit using one wire each from 2 separate pairs in the cable. Eg, if you accidentally swapped pins 2&3 at both ends then you'd have split pairs with one wire from the orange pair and one from the green pair in a circuit.

BTW - you haven't said what speed the connection to the radio runs at. If it's gigabit (1000Mbps) then it uses all 4 pairs, rather than just 2 pairs as used by 100Mbps.

 

[SparkyTris]

thanks for all input.
the radio is for sure only 100 mbit the lappie is bran new though so I suppose it could be putting signal on all wires.
yes, as you say the SNR on the freeview only falls off when we connect the lappie, not the radio.
the lappie I have since discovered is not earthed. (the PSU is not earthed).
thinking about it, I am not sure how these floating-chassis equipments have been allowed to become so prevalent.

 

[SimonH2]

the lappie I have since discovered is not earthed. (the PSU is not earthed).
thinking about it, I am not sure how these floating-chassis equipments have been allowed to become so prevalent.

It's come up here a few times. With my Apple laptop, if I use the "duck head" adapter it doesn't earth the PSU and I can measure over 90V between case and earth with my high impedance DMM I normally use a cable with earth connection to the PSU, otherwise I get a quite uncomfortable "tingling" in my palms when I'm using it.

Thing is, there's a tiny but none-zero leakage current from almost all electrics - as long as it's below a certain level then it's considered "safe".

As an experiment, what happens if you earth the laptop ? Connect a single core cable from an accessible case screw on the chassis to the earth pin in a 13A plug. If there's a VGA socket then a connection to one of the retaining screw sockets would do, otherwise see what there is.

 

[SparkyTris]

whats the deal with cat5e & cat6? will cat5e plugs go into a cat6 socket? or is there some keying to make it impossible?

what does "keystone" mean?

cheers

 

[bernardgreen]

I am not sure how these floating-chassis equipments have been allowed to become so prevalent.

You youngsters...... us oldies remember radios where the chassis was connected to one side of the 240 volt mains supply coming from a non polarised bayonet plug plugged into the lamp holder.

Some radios used a resistive conductor in the mains cord to drop the mains voltage low enough to supply the valve heaters.

Nostalgia http://www.bvws.org.uk/405alive/tech/safety.html


http://radioether.blogspot.co.uk/2008/02/replacing-line-cord-resistor.html

 

[SimonH2]

whats the deal with cat5e & cat6? will cat5e plugs go into a cat6 socket? or is there some keying to make it impossible?

Yes, Cat5, Cat5e, Cat6 all have the same style of plug - commonly, but technically incorrectly, called "RJ45". So you can have Cat6 fixed cabling and use Cat5e patch cables if you don't need the extra capabilities.

what does "keystone" mean?

It refers to a style of patch panel where the panel is "unloaded", you terminate each connector to the cable and clip it into the panel. The alternative, and I think more common, is to have a patch panel where all the connectors are built into the panel and the cables are terminated to the back of the panel in-situ.

If you refer to the photos I posted a couple of posts ago, on the left you can see a partially populated panel. In this style (Nexans 808HD), the connectors clip into a frame and then the front panel is fitted on the front. Here, I'm using the front panel to hold the unterminated cables by poking them through the holes.

 

[SparkyTris]

thanks v much for all help; every day is a school day.
when I went into the loft all tooled up with my metal RJ45 gear the first thing I came across was an inline coupler for the TV coax.... uncoupled.
that sorted out the TV SNR issue; nothing to do with the Ethernet modifications.