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I am doing some rewiring of our internal phone lines (almost entirely removal of unused lines). The issues we have run into is the router will every now and then simply not connect from the house to our provider.

The wire from the NID to the router is an old, very thin 4 wire phone cable (GRBY wires). I am going to replace it whether it is the culprit or not. The outer sheath is getting brittle.

The plan is to use an outdoor UV gel filled Cat5e to go from the NID to inside the house, then Cat5e from a box there to the router (or maybe just gel filled all the way, it's a fairly wet basement). This is an old house and the cable will run near and across many power cables.

Given the possible interference would it be worth it to double up cables from the NID to the router (i.e. use blue/blwh together for ring and orange/orwh together for tip)?

I'm not exactly clear how the twists work with data communication so maybe it would be better to use blue/orange and blwh/orwh instead?

Would this even help with possible interference or signal strength?

Simurr
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  • no, that sounds like it would be worse; the pairs are designed to eliminate crosstalk. if you take away the pairing, it would get worse. use cat6 if in doubt: it separates the pairs with a small plastic crossbar. – dandavis Aug 28 '17 at 19:37
  • crosstalk with what? there is nothing else on this wire. 6 of the 8 wires would be disconnected with only one dsl line. If there is an issue with how the twists are designed I also asked about using them paired blue/orange for ring, blwh/orwh for tip if that's what you are talking about. – Simurr Aug 28 '17 at 20:09

2 Answers2

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Given the possible interference would it be worth it to double up cables from the NID to the router (i.e. use blue/blwh together for ring and orange/orwh together for tip)?

No.

Besides what asndre said, which is true, if you put two transmission lines in parallel, the following occurs:

  • Impedance is halved, so it will be mismatched.

  • Since one line will always be a little bit longer than the other, the signal at the end will be the sum of both, therefore it will include two copies of the original signal, summed with a slight delay, which will degrade signal integrity.

In other words, use good quality outdoors-proof waterproof twisted pair telephone cable, with the same impedance as the original phone cable. It'll work fine. The less connection boxes on the way, the better.

If you think you might someday need to put a connection box somewhere on the cable, simply reserve a meter extra cable at this point, coiled. If you use conduits (you should) then keep a bit of extra of cable at the end that you can pull through the conduit if you need to cut it in the middle to install an extra connection box.

bobflux
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It is very bad idea to use Cat5e-based wiring/cabling to establish a xDSL connection.

Cat5e wiring is not designed for so low frequencies and therefore does not feature an appropriate characteristic impedance (i.e. Z(f)) at the frequencies employed by xDSL which works in telephone line bandwidth (<20 kHz).

Using Cat5e for xDSL also results in dramatical signal attenuation, about 3~5 times worser comparing with an appropriate cable/wire.

To be short, POTN is about 600-Ohm techniques while Cat5e if for 100-Ohm ones.

asndre
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  • How do you figure? Copper is copper and the wire gauge is the same as Cat3. This was going over old untwisted 4 wire cable that was also 24AWG. – Simurr Nov 09 '17 at 22:29
  • @Simurr Cat5e is not specified for so low frequencies. For example, G.SHDSL works in 0-400 kHz bandwidth at 2 Mbps and 0-125 kHz at 640 kbps. Cat5e is specified beginning from 1 MHz. – asndre Nov 10 '17 at 18:59
  • @Simurr Copper as material and wire gauge as square dimension define the DC resistance on the cable. But is this the only parameter significant for proper transmission? What about characteristic impedance, Z(f), which defines the cable AC characteristics significant for transmission? – asndre Nov 10 '17 at 19:02
  • @Simurr The figure i shown, 3~5 times, is from my own practice with G.SHDSL lines. I was very surprised too the first time i face that, but the difference in the cable AC characteristics between what the G.SHDSL standard expects and what a Cat5e medium provides, gives a well-grounded explanation on this. – asndre Nov 10 '17 at 19:10
  • Thank you, that was very helpful. I do find it kind of annoying that everywhere else I've looked and everyone I've talked to says Cat5 wire is the way to go (future proofing?). I'm using it and it's working but I'm guessing it really depends on your total wire distance and how much signal degradation you can handle. If I have the time and the cable I may do some more extensive testing. – Simurr Feb 26 '18 at 16:47
  • What is the effect of the impedance mismatch, besides signal attenuation? – LarsH Dec 29 '18 at 12:45
  • @LarsH Signal distortion due to (multiple) reflections. – asndre Dec 29 '18 at 13:09
  • @asndre: Thanks for your quick answer. I've posted a related question at https://electronics.stackexchange.com/questions/414286/when-can-i-use-cat5e-wiring-to-carry-a-pots-signal-to-a-dsl-modem – LarsH Dec 29 '18 at 13:11
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    I do an awful **LOT** of audio and Production Intercom for Live broadcast events. My standard disposable long-run interconnect cable is cat-5. I will often use 30 or 40 boxes of cat-5 cable. I simply treat the cable as 4 very high quality twisted pairs. And it works incredibly well. – Dwayne Reid Dec 29 '18 at 21:19
  • @DwayneReid How long are the distances you need to span? What is the signal you called "audio and p.i." (spectra, modulation, protocol, etc...)? In this question we speak about xDSL signaling intended to cover kms, not a stage. Why you are so confident claiming that you experience related to some "audio on stage" could be applicable to an another field of technology? – asndre Dec 30 '18 at 09:09
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    @asndre: distances range from perhaps 100m to 700m or more (300' - 2500'). Baseband audio. **BUT** I have also done ADSL modems at the end of long runs of a single pair of cat-5 cable. No issues at all. – Dwayne Reid Dec 30 '18 at 16:27
  • @DwayneReid Baseband audio is out of the scope of this question. It is about DSL (the OP did not specify the exact type within the numerous DSL family). In the scope of ADSL modems you mentioned, how long were your "runs of a single pair of cat-5 cable"? Not greater than 305 m (the nominal length of a boxed Cat 5e cable)? What do you mean speaking "No issues at all"? Did you perform some (comparative) measurements? Or simply install and see the link LED on? What were up/down speed, line loss, SNR, BER, another measurable params of the link if you know/measure? Please explain your experience. – asndre Dec 30 '18 at 19:51
  • xDSL is not operating at audio frequencies <20kHz. The first bin is 25kHz and goes up to 1.1MHz. – Jack Creasey Dec 30 '18 at 20:12
  • @JackCreasey Which one of the xDSL family? (please be careful, the OP does not specify the certain type of DSL in this question). In any case, you are wrong. The explanation is below. – asndre Dec 31 '18 at 08:27
  • @JackCreasey To establish an xDSL connection, the (mandatory) G.HS procedure is used. As per ITU-T Rec. G.994.1, the lowest carrier G.HS is able to use, is 3*4=12 kHz (BPSK) carrier for G.991.2 xDSL Recs. – asndre Dec 31 '18 at 08:33
  • @JackCreasey As per ITU-T Rec. G.991.1, HSDL psd mask has a limit of -20 dBm/Hz at 4 kHz. – asndre Dec 31 '18 at 08:55
  • @JackCreasey As per ITU-T Rec. G.991.2, SHDSL psd mask has a limit of -30 dBm/Hz at 0 Hz (DC). – asndre Dec 31 '18 at 08:57
  • @JackCreasey As per ITU-T Rec. G.992.1, ADSL psd mask has limits of -92.5 dBm/Hz at 4 kHz and -36.5 dBm/Hz at 25.875 kHz with slope of 21.5 dB/octave in between these points. You can say that -92.5 dBm/Hz is so low but ITU-T Rec.99 thinks not, stating "_The step in the PSD mask at 4 kHz is to protect V.90 performance. Originally, the PSD mask continued the 21.5 dB/octave slope below 4 kHz hitting a floor of –97.5 dBm/Hz at 3400 Hz. It was recognized that this might impact V.90 performance, and so the floor was extended to 4 kHz._" – asndre Dec 31 '18 at 09:04
  • @JackCreasey Have you at least one grounded argument behind your claim that "xDSL is not operating at audio frequencies <20kHz"? (I think you have not.) _Maybe you want to say only that ADSL is (strongly) limited to not operate in the (POTS) voice (up to 4 kHz) band?_ – asndre Dec 31 '18 at 09:23
  • @asndre: Have **YOU** actually tried to use cat-5 cable as the telco line into a DSL modem and had problems? I see you spouting a lot of theory why it won't work but do you have actual experience where it does not work? What I can tell you is that I have had no problem doing exactly that. Telus ADSL in Northern Alberta. – Dwayne Reid Jan 01 '19 at 02:22
  • @DwayneReid I never said "it won't work" (i said "It is very bad idea". do you thing these two are equal?) and described my experience in the early comments (i see you did not read neither the answer, nor comments...). Yes, my experience is not absolute, it is (very?) conditional because it is related (only?) to kms-long G.SHDSL-enabled lines. Therefore, the primary factory when i'm asking about your/other customer/engineering experience is the distance of a DSL link you/other covered by a cable of the selected type. Now can you answer my question i asked you in the comment above? – asndre Jan 01 '19 at 15:42
  • @asndre: distances between Telco demark block and ADSL modem typically less than 100m. Sometimes much less. Typical North American homes and small business buildings. – Dwayne Reid Jan 01 '19 at 21:34
  • @asndre: I honestly don't want to start an argument with you. But I disagree with pretty much everything that you said in your answer. You specifically said that "cat-5 is not designed for such low frequencies". I categorically dispute that statement. And most of the old Telco wire that I have encountered in the past does not have a specific impedance. There is a huge difference between the Telco cable used for distribution (both underground and aerial) and what has been installed in homes and businesses – Dwayne Reid Jan 01 '19 at 21:42
  • @DwayneReid The OP does not specify neither the certain typed of DSL he/she use, nor the distance he/she needs to cover. Therefore then I answered the question I assumed (over-perceived as I see now, thank you for clarification) the distance could be (very) long (km+) and comparable with what you called “distribution cable” in length. – asndre Jan 02 '19 at 11:06