RJ11 cables and their effect on Speed and Dropouts

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Posts: 15
Joined: Mon Jul 08, 2019 4:04 pm

RJ11 cables and their effect on Speed and Dropouts

Post by BFUMXXXX » Wed Jul 17, 2019 5:54 pm

I have a Billion 8800NL R2 used as a modem (bridge mode for FTTC connection) absolutely no problems with this over the last five months since install.

I have read a lot about R11 cables (socket to modem/router) length, twisted wires or not gold contacts etc.

Initially (with some experience of both IT and electronics) I totally dismissed the fact that a short RJ11 cable between the face plate and the modem would make any difference at all to speed or reliability. Why should it when the green cabinet was 500m away and joined to the house with unscreened twisted pairs all bundled together then untwisted cable for 20m from the pole to the house.

Although a better cable may not be the solution a problem with "upload" not so much with download made me think again. Download was and is fairly steady around 38 Mbit/sec. Upload was nearly ten, dropped to 8 ish and then dropped to 0.9 .

Nothing had changed or so I thought. Then when the ISP added comments to my ticket I saw ...

"Interference Pattern Regular Interference Observed Daily" but qualified with "SERVICE IMPACT.... No impact observed" (ok maybe means line didn't drop)

Then the penny dropped....

A. I have lots of RJ11 cables and you can't see if they are made with twisted pair cable without cutting them open. None I have seen are screened.

B. This final few feet of the 500m connection from the green box runs past mains wires, the DECT phone, LED lights, other equipment with WiFi like the printer etc. etc. Plus PCs with their lousy switching mode power supplies. LED lights are low voltage dc right? Yes, but how do we get this from 230v ac? Via a cheap noisy power supply and this noise is probably transferred on the long wires to led strip itself.

C. In all the RJ11 is likely close to any number of other things too, microwave, central heating pump and thermostat and so on.

There are different kinds of electrical noise (one-off spikes {the central heating thermostat}, and constant noise {power supplies} and something in between like the microwave and vacuum cleaner) and it is mostly in your home and almost certainly close to the phone line, I don't have phone extension sockets but a lot of people do, so add this to the list even if the old bell wire is disconnected. This long bell wire acted like an aerial picking up noise.

Cutting open a spare RJ11 cable I found it used just straight wires not twisted. Two things in a cable design {ok probably more} help reduce the noise picked up, twisting the wires and screening {like cat-6 cable is I'm told}. Making the cable as short as possible helps too. OK radio fanatics will dispute this based on half wavelengths or something (only kidding) .


There is potential a lot of electrical interference close to the RJ11 cable from socket to modem/router.

I moved the DECT phone, turned off the LED lights, moved the Billion to within a foot of the wall socket, and coiled the RJ11 cable (will make a new cable instead of using a supplied one when my RJ11 plugs arrived tomorrow) Result, upload remains at 8.4 (it suddenly hit 8.4 after being 0.9 a couple of hours ago) download is 39.x almost 2 Mbps faster than I have had for months.

If upload remains at 8.x by tomorrow then I can reasonably assume that interference was the problem. This will confirm if twisted pair and a short cable really do make a difference. I don't think that gold contacts make much difference, just use contact cleaner and/or unplug and plug in again once a year.

Should you pay a fortune for a special RJ11 ultra-fast cable? Regardless of the outcome of my experiments NO ! The problem with advertised cables is that they don't tell you what the actual spec is (like twisted cables or not) and I have not seen a screened one as yet. I don't know the spec of the cable supplied with the Billion, it's lost in my pile of cables in the draw.

I plan to make a new RJ11 cable from two connectors costing pennies and a piece of Cat-5e cable I have, this will be a foot or less long as the modem will sit right by the socket. Once I have a piece of screened cable I will make another and see if this makes any further difference, just remember to ground the screen (ok what to?) at one end only.

More info as I get some results or not, comments welcome, please refute anything or all of this !!

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Re: RJ11 cables and their effect on Speed and Dropouts

Post by BFUMXXXX » Sun Aug 04, 2019 8:13 am

? Video ?

Was this a reply to the RJ11 noise post?

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Joined: Mon Jan 29, 2018 11:27 am

Re: RJ11 cables and their effect on Speed and Dropouts

Post by youngsyp » Wed Aug 28, 2019 10:51 am

I make my own DSL cables (RJ11 is a type of plug, not cable), using BT CW1308 (2 pair UTP) cable, an RJ11 plug (gateway end) and RJ45 (master socket/ SSFP end). I've recently started using a cable directly from the gateway to the test socket of my master socket, and the for the master socket end, I use a BT 431A plug.
In the past, when on an ADSL service, I did see imporvements in downstream sync rates with these cables, over the typical mass produced non twisted pair DSL cables. I couldn't comment on any improvements these days though, as I've always used these cables on my FTTC service. However, tis type of cable is a benchmark and costs peanuts to make.

My line is overhead fed from the street pole and I also use the external equivalent of CW1308 (CW1724), from where the overhead cable terminates to the back of my master socket. It may not offer any improvement over any other type of cable but, you know where you stand using it, which is good enough for me.

From my research, you're wasting your time and money with screened cable. Not only do you have to construct the cable in a much more intricate manner, with the applicable plugs (I don't thing there's such a thing as a screened RJ11 plug?!) but, UTP cable is designed to throw off interference itself.

Both cable types and all plug types are freely available from a number of places, including eBay.


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Joined: Mon Jul 08, 2019 4:04 pm

Re: RJ11 cables and their effect on Speed and Dropouts

Post by BFUMXXXX » Wed Aug 28, 2019 11:47 am

Wow, I didn't know that RJ-11 was a plug, I thought it referred to the whole cable, like "This is an RJ-11 cable" I will be more careful next time!.

Perhaps for the benefit of some of use you could explain the BT CW1308 (two pair) and how this {when the circuit only needs one pair? } how this benefits the connection? Maybe mine don't work too well as I only have a single (twisted) pair?

I also don't know my SSFP from my CW1724, but I guess most people do ? I know my MK3 master socket has a RJ-11 socket (right this time?) which goes to the RJ-11 socket on my modem. (Ok it isn't really a modulator / demodulator is it but people call it that I know)

Interested to know more about your research on screened cables as it's not the experience most of the electronics engineers I know have had, maybe there are different circumstances with noise on phone lines and the floating nature of the circuit? Were you grounding the screen to earth or signal ground? Do you have any measurements?

A more detailed description of "throwing off" would be good too! Is this related to inductive induced noise or capacitive coupling ?

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