Copper Clad Steel "CW1308"

[Dave Liquorice]

Tidied up the incoming phone line today. The house rewire included a couple of Cat5e's and some CW1308 from the NTE to the eventual cable/distribution point.

Strip back the CW1308 and think these cores are a bit stiff, wire everything back up. POTS works fine, good level, no audible noise, hum, crackles, etc.

ADSL2 (up to 8 Meg) on the other hand is not happy. Daytime sync rate was persistently 1 Mbps lower than previous that had bee rock steady at just over 6 Mbps (not bad to 3 miles of old ali). Looking at the plot of the number of symbols/carrier it is obvious that LF and MF broadcast stations are really clobbering things. It's now got dark and it's even worse, sync rate 2.5 Mbps lower and basically no symbols being above about 500 kHz, the MF band starts at 526.5 kHz...

All I've done is shorten the dropwire by 3 yards, and use this new bit of "CW1308". The wiring down to the current location of the ADSL modem is unchanged. Close inspection of the new CW1308 shows it to be copper clad steel, yes steel, not ali, it is magnetic.

Could this dubious bit of CCS be better at receiving the MF interference, have a funny resistance/impedance or perhaps joints to it doing "odd" things? I can't think how but the ADSL is definatly suffering a lot of MF interference.

Everyone home now and taking down the 'net connection would not be conducive to family harmony. Tommorow I'll switch to a pair in one of the (copper) Cat5e's and see what happens. Most odd and be interested in others thoughts.

[fred]

In article , Dave Liquorice writes

A quick punt:

From memory, the CW1308 spec specifically specifies copper so anything but copper is not to spec.[1]

Steel is too hard to give a gas tight seal on IDC so will be more likely to corrosion and poor joints in the long (and possibly short) term.

I can't see it being more susceptible to induced interference though as it will still be cancelled in the return leg.

Skin depth at ADSL freqs, pass.

[1] or at least specifies a loop resistance that steel cannot meet.

[Peter Crosland]

It is a potentially (no pun intended) a bad move altering BT's wiring. Medium wave interference increases after dark and a drop of 3 or more dB is quite common and once could say normal. Also shortening the cable could just have altered the resonant frequency of the incoming cable to make matters worse. BT are likely to charge heavily if they have to put matters right.

[Graham.]

My reading of his post is he has not touched the BT side of his NTE5, and even if he has, I imagine Dave will be as circumspect as you or I if BT ever see his installation.

[Chris Bartram]

On 24/09/13 21:02, fred wrote: [snip]

Plus, I'd imagine the steel itself will rust far too easily.

Is it possible since this cable is crappy, the twist isn't to spec either, so any common-mode interference may be worse?

[Dave Liquorice]

Agreed I plotted the diurnal SN ratio here when the ADSL first arrived and was messing about with different filters. At that time 6 dB variation in SN day to night was normal. Of the filters one gave better rates during the day but couldn't maintain that rate overnight. Another wasn't quite as good during the day but could sustain the rate during the night so overall produced a better result. Yes, I do know that the ADSL is the unfiltered side but hanging loads of C's and L's across the line does affect it...

That thought has sort of passed through my mind but I'd expect if it was a resonance thing to just notch out a fairly narrow band of carriers. Now, at night, there is a very distinct drop off at the start of the MF broadcast band. It's a broadband of interference that is getting in somehow.

We tend to get the same Openreach engineers and they know me and what my day job is and used to involve(*). They haven't batted an eyelid over the building attachment point moving from the facia to the stonework 6' to the right, the NTE moving from downstairs to upstairs etc.

Now prepared one of the Cat5e's to use tommorow. I did notice that my tone tracer picks up a fair bit of shash from the live phone cable, which sort of surprised me but I don't know if that is normal. If anyone has a tone tracer probe and can wave it near an ADSL enabled line what do you get?

(*) Outside Broadcasts, many a time perched up a ladder connecting various lines to a block, controls, DELs, musics etc. Not pleasant when soaking wet and you haven't worked out which pairs of the block have DELs on 'em... Doesn't happen now, BT van turns up to interface the OB truck to BT fibre. They also pick up the ISDNs or DELs (some with ADSL) and hand them over down a multi.

[Dave Liquorice]

short)

The slight staining on the insulation at the cut ends was another hint along with the stifness that this wire wasn't copper. That end is under screw terminals, the other end (at the NTE) was cut back about 6" before being punched down into a many time used IDC on the back for the NTE's lower half face plate.

The twist looked good, a lot tighter than I've seen on some samples of telephone cable. Very similar to that of Cat5. Hum, all the pairs looked very much the same though and the cable sheath has a very uniform pattern. Unlike Cat5 where each pair has a different twist pitch, to minimise crosstalk and which gives that bobbly nature to Cat5 sheaths.

[Mike Tomlinson]

En el artículo , Dave Liquorice escribió:

You might have unintentionally shortened it to a length where it becomes a more efficient antenna for receiving MF. I'd certainly go with your suggestion of trying a length of Cat5 as a replacement to see if that improves things.

You comment about punching down into a "many time used" IDC on the back of the NTE faceplate made me wonder if it's simply worn out and the connection is poor. They're not designed for many insertions/removals.

[John Rumm]

You are probably hearing the ADSL - it can sound like background hiss if accidentally demodulated somewhere.

I will try tomorrow and let you know...

[Andy Wade]

Well, the skin depth in copper at 500 kHz is about 0.1 mm. CW1308 conductors are 0.5 mm dia (IIRC) which would make the RF resistance roughly 0.1 ohm per metre.

For steel the calculation isn't so easy since the key parameters (resistivity and relative permeability) vary wildly depending on the alloy, state of temper, etc. For a stab in the dark I'll use a resistivity of 10E-8 ohm-metre (Kaye & Laby, for mild steel) and 100 for the permeability (Wikipedia for unspecified carbon steel). This gives a skin depth of ~20 microns and an RF resistance of circa 3 ohms/m. (This is ignoring the copper coating which may or may not be insignificantly thin).

That's a factor of 30 on resistance of this section, but its probably insignificant compared to the overall exchange loop. Another factor is that the steel section will be quite inductive (the line's Zo will be higher) and this will introduce some more attenuation.

Dave - does your modem/router show line attenuation figures and have they increased?

The steel will have to go though. These fake cables are nothing but trouble...

[Dave Liquorice]

More effcient from 500 kHz (600 m) to 1.6 MHz (180 m) by just removing 3 m overall? Most of the line (nearly 3 miles) is under ground the last 50 m or so is above but I really don't see such small overall change in length making such a dramatic difference over such a large frequency range.

Was going to do that this morning. Last night I'd prepared the ends and checked a junction box that had some IDCs that had not been messed with and I podged again "just in case". Made no difference to the reported SN ratio or the awful symbols/carrier plot. I didn't reset the ADSL though. This morning before doing the swap I power cycled the ADSL modem and it's come back up good and solid.

Bollocks! I don't know if there was a dodgey connection, if the modem had got it's knickers in a twist or if the modem doesn't truely show the current line conditions. It will be interesting to see what happens tonight. Still don't like the idea of the steel wire though, but in the interests of "if it ain't broke, don't fix it" it'll stay in service for the time being.

[Dave Liquorice]

cable,

It's that "accidental demodulation" that worries me ... TBH with ADSL not starting until 25 kHz and the line being balanced I wouldn't expect to hear anything with a tone trace probe. The noise was detectable a couple of inches from the cable.

This morning after the reboot and sync at 6720 the noise is still there but "cleaner" and more of a buzz than a "bussy shash".

[Dave Liquorice]

When talking about 20 microns I should imagine the copper plating to be significant.

No the line attenuation figures are the same at either 44 or 45 dB down stream. It's just (was...) an awful lot of added MF noise screwing up the SN ratio.

[The Natural Philosopher]

I can assure you that ADSL always puts audible mush on the line.

Even on a good one.

Iv'e got a very good one - well over a mile to the exchgange and 6Mbps+ speeds. But if I make a phone call and then halfway through pull the router off, you can hear the mush vanish.

And I am not sure you need non linearity to hear it either.Ther ADSDL is in lots of RF channels all of which are constantly varying in amplitude or phase or something. The chances that these will all equal zero ALL of the time is zero. Otherwise there would be no RF. And the chances that they will AVERAGE to zero BELOW say 10khz is whilst larger, still not zero.

If you want a clean voice line, use VOIP!

[Adrian]

What filters are you using? Cheapies that came with a router? Might be worth getting some decent quality ones from a specialist source, see what happens.

[The Natural Philosopher]

Nope. Have a quality face plate and no matter how many filters I added in before the phone (I had three at one point, in series) the mush stayed. Its not RF. it's audio. And the router/DSLAM puts it there. Its probably not intermodulation at all, but pure MODULATION.

Its not massive - 50db or more down on a normal voice level, but compared with VOIP or a non ADSL line, its there.

[John Rumm]

It could be a feature of your particular router - must admit I have not done any comparisons as to whether some stick more noise back into the audio than others, but it seems like a fair bet there will be a variation.

[Theo Markettos]

Will BT really come round and retune your line length if you happen to have hit a frequency null? I thought ADSL was supposed to train and pick its frequencies to avoid any nulls on the line? Which could be a point actually - if the exchange hasn't noticed your line profile has changed, the old one could be hitting nulls. How do you force the exchange to retrain? Can you do it by power-cycling the modem umpteen times to convince the DSLAM that something is up?

Theo

[fred]

In article , tony sayer writes

In short, CCS is shit!

I wasn't too far off on my initial points CW1308 _must_ be copper and IDC manufacturers will not guarantee a reliable connection with anything else.

Mumbles of 'passing off'.

pdf

[Dave Liquorice]

My comments were refering to using a non-contact tone tracer probe not listening to the line with an instrument. Directly listening to the line there is no noise or shash but there is a low level hum. I shall experiment later and report back, but, IIRC, that low level hum was present before we had ADSL.