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[les-70]

   Thanks for the results. The very large degradation with the 400m suggests something must be wrong.    The resistance does seem high and since the the TDR did not show bad joints I wonder if the cable is not solid copper.  One reference gives -"The conductor resistance of CCS telephone cables with 1/0.5mm diameter conductors is confirmed as around 700Ω/km. CW 1308 defines a maximum conductor resistance for a 1/0.5mm conductor as 97.8Ω/km".  If it is copper coated steel that may be the issue.  A magnet is the simple test!.

 Otherwise it may be impedance mismatch causing a bounce of the signal up and down the 400m. The 338ohms ought however to be attenuating any reflection.  Asbo went to a lot of trouble with baluns doing similar tests but I have never really understand why it might be critical especially in a test in which only the firmware is changed.

   Edit: In fact given a skin effect at high frequencies I am not sure how much the resistance tells us.

   

[burakkucat]

I agree with you that there is a background niggle that something is "not right". 

Thank you for providing the relevant details from the CW1308 specifications. Perhaps I may eventually get around to some further investigations. Starting with a magnet . . . 

Regarding Asbokid's testing, he only used a balun to connect a noise generator to the pair. The various attenuators that he inserted into the circuit were of the classic resistive Pi design, each built to provide a know dB value insertion loss.

[burakkucat]

The reel of CW1308 cable was placed in an accessible location and each end -- of each of the three pairs -- was prepared to allow connection to the Ohmmeter 18C.

Insulation Resistance

Green pair    0    Ohms
Blue pair      0    Ohms
Orange pair  1 MOhms

Loop Resistance

Green wire 1    58 - 59 Ohms
Green wire 2    55 Ohms
Blue wire 1      53 - 54 Ohms
Blue wire 2      55 - 56 Ohms
Orange wire 1  54 Ohms
Orange wire 2  54 - 55 Ohms

   

[burakkucat]

Further testing (with a fridge magnet) confirmed that the conductors are made of copper coated steel! 

The Ohmmeter 18C was deployed, once again --

Insulation Resistance

Green pair    0 Ohms
Blue pair      0 Ohms
Orange pair  0.5 M Ohms

Loop Resistance

Green pair        92 Ohms
Blue pair         123.3 Ohms
Orange pair  > 9999 Ohms

b*cat is very grumpy. 

[les-70]

  Sorry your grumpy but the best place for it is stored on a coil rather than in use. Always a bright side!  I have some runs of the stuff in my house - just on telephone extensions that are not actually in use. If I ever replace them I will be with solid copper ethernet cable as the locations would be good ones for ethernet round the house.  I did once have the modem at the end of the stuff and adding about 15m of CCS to a 1km line only made a small difference of about 0.5db in snrm.   It is better than anything untwisted but one of the worst features is supposed be long term corrosion in Krone joints.

   I guess The CCS provides some explanation of the results

[burakkucat]

The only thing we can gain from this sorry tale is the typical data obtained from an appalling 400 metres local loop. 

(The performance will be very familiar to Walter, from his experiences in trundling his wheelbarrow around and about in Ewhurstshire.)

What has amazed me is the loop resistance results. Considering that one would expect an open-circuit pair to show infinity, the green and blue pairs are clearly useless.

The orange pair is not that good, either. The insulation resistance has halved between the two successive measurements!

[burakkucat]

Some final comments on that spool of (supposedly) CW1308 specification cable.

• Making use of a magnet (with thanks to Les for the suggestion) showed that the wires were not solid copper but just copper coated steel cores.
• The cable was carefully de-spooled with the idea to check the "far end" for any potential damage. None was found.
• During the de-spooling process it was observed that there are distance markers on the outer sheath. The physical length of that cable is actually 100 metres.    The fact that the TDR determined length (of the three pairs, serialised) was more than three times the physical length, also shows that there is some significant defect in the cable.

If any Kitizen would like to have that spool of cable -- for experimental purposes, to mimic the poor Openreach D-side cabling perhaps (such as can be found in Ewhurst, Surrey, for example) -- then it will be free to s/he who wishes to collect it from The Cattery, Off DP1032, Via P28, EABSE. I will also be prepared to send it, via courier, to any UK address in exchange for the shipping cost. 

[Darren]

Unlucky on that cable burakkucat. Still interesting to see the results against a dodgy cable though.

FYI, on all new cable I buy the first thing I do is strip back a few inches of the sheath and scrape a stanley blade along the core, if silver starts to shine through it goes back or in the recycling. A magnet is a good idea but it won't detect copper coated aluminium

[burakkucat]

A magnet is a good idea but it won't detect copper coated aluminium

Indeed. That had occurred to me but I had failed to make a note of it here. Thank you for adding the detail. 

[Darren]

No problem