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[JGO]

The reference on connectors is, to put it politely, misleading.

A connector on an otherwise perfectly matched cable causes two equal and opposite reflections, at each end. This means that to detect them you have to look when the signal changes and very quickly :=

Say these are 1 cm apart then the nett reflection is about 1/20000 micro sec long if cable velocity is 200 metres/microsecond, = 0.05 of a microsecond !!

   With a 5 MHz bandwidth the response time time 0.7/5 microsec = 0.12, so they are smeared  out and are invisible.  This is why such connectors have been  standard on UK TV receivers for years- the reflections are negligible  for practical purposes. TNC and BNC connectors are better, but would show no practical advantage and cost more.

In the case of xDSL the bandwidth is similar but split into 4 kHz sections - which complicates the calculations.

Many factors can have an effect but plugging in numbers shows when they are negligible - like the 30lb reduction in weight of the RMS Queen Mary when the moon was overhead !!   


 

[konrado5]

A connector on an otherwise perfectly matched cable causes two equal and opposite reflections, at each end. This means that to detect them you have to look when the signal changes and very quickly :=

Does it implicates that signl reflections caused by connectors would be not noticable in Hlog?

[JGO]

 I don't see a way for the reflections from a socket to be significant on  ADSL. Also statements you quote from the article seem imprecise to me so I plugged in the numbers.

 I don't know Hlog at all but I have some other monitoring software, which has indicated 80 bits/tone !  By my calculation this requires about 500 dB S/N to work which implies 3e30 watts into the modem ! 

I DON'T HAVE 100% FAITH IN MONITORING SOFTWARE . 
   

[konrado5]

In this book there are many loop attenuations graphs: some graphs are mix of several copper pairs but I don't see "undulations", for example on ETSI #5 line.
Page 71-77
http://bookzz.org/dl/461158/e2fb44

[konrado5]

A moderate HR joint will be visible on a time domain reflectometry (TDR) as a pronounced cable-gauge change, and some modern test systems attempt to exploit this to determine the presence of HR joints.

Page 246:
http://bookzz.org/dl/494442/ed9e82

[boost]

A moderate HR joint will be visible on a time domain reflectometry (TDR) as a pronounced cable-gauge change, and some modern test systems attempt to exploit this to determine the presence of HR joints.

Page 246:
http://bookzz.org/dl/494442/ed9e82

Thanks for the book - that will come in handy!

[konrado5]

Unfortunately I've found Hlog graph of circuit ETSI loop 5 with mixture of gauges without "undulations". This is mixture of gauges: 0.5 KM 0.90 mm, 0.5 KM 0.63 mm, 0.75 KM 0.5 mm and X KM 0.4 mm).
Page 9:
http://www.lea.ufpa.br/producaocientifica/seminarios/Loop_Characterization_by_Frequency_and_Impulse_Responses.pdf
 

[konrado5]

Line with bridged taps Hlog on page 14:
http://www.ewh.ieee.org/r6/scv/comsoc/9909.pdf
It seems to me that my "roll" is the similar to bridge tap Hlog.

I attach once again Hlog because at the past I've attached bad Hlog (with improper upstream graph).
Best regards
konrado5

[burakkucat]

Yes, I can see the similarity between the graph shown on P14 of the PDF file and your latest attached Hlog graph.

It is unfortunate that the area of most interest (in your graph) is located in the region between the US and DS frequencies where a notch is often observed.

I have attached the Hlog plot for my own line, operating in ADSL2 (not ADSL2+) mode. That notch is not due to a line deficiency or fault but just a consequence of the power spectral shaping between the US and DS frequencies.

[konrado5]

But I think about "roll" next to notch. What do you think about reply #21 and earlier?

[burakkucat]

The document that you have discovered and mentioned in #21 does, I admit, not show any significant graphical features for changes in wire gauges at the scale in question.

If you are asking me for my further thoughts on the observation I will say that, although impedance changes do occur with changes in wire gauge, it could be that the undulating roll towards the higher frequencies in your Hlog plot are the secondary (and higher) effect of the presence of a bridging tap at the lower frequency end of the plot. However it is inconclusive due to the dip that is often apparent when transitioning from the US frequencies to the DS frequencies. To be honest, a TDR (or FDR) trace may give a better idea of what is occurring.

[konrado5]

Thank you very much for reply. Could you again compare my two Hlog graphs: hlogdiagmode5.png and onedayhlog.png (temporary signal peturbations caused by pavement workers - without correct upstrem datas but upstream attenuation was then 20.2 dB instead 14.8 dB)? On onedayhlog.png the "roll" is significantly smaller but it is very probable that reflections from the "roll" was moved to the upstream frequiences (20.2 dB upstream). Moreover, I see on onedayhlog.png some other changes, for example nearly tone 250. Is it possible that this day pavement workers temporary disconnected bridge tap? That one day I had the same stability, I had only about 400 kbps higher downstream rate and 60 kbps lower upstream rate.

Best regards
konrado5

[boost]

Keep the articles coming K5, they're great!

Well done on finding a HLOG for known bridge taps, too, that's very handy tbh.

Your graphs continue to be difficult to read due to the resolution and x axis labeling

In my opinion, they need to be much more granular 'at a glance' or people give up. I want to see them and I've given up on several because they hurt my eyes!

[burakkucat]

I really cannot extract any further information from the latest graphs that you have shown.

I believe that some damage was caused to the cable by the pavement works? I seem to recall (without searching back for it) that you posted an image of the cable with damage to the outer sheath and the inner conductors left exposed. Any such physical perturbation of the cable could be the cause of changes in electrical parameters currently being monitored.

As I have said before, it is a very difficult task (almost impossible) to remotely diagnose potential faults in a circuit. It really requires someone to physically attach various items of test equipment and make measurements. Do you think that the pavement could be dug up, once again, this time to inspect the cable (and possibly replace a section of it)? Because, no, I don't! 

[konrado5]

seem to recall (without searching back for it) that you posted an image of the cable with damage to the outer sheath and the inner conductors left exposed.

This is other issue and other day. When pavement workers damaged my cable I've had no Internet connection but repeated connection didn't change anything.

When pavement workers temporary peturbed my circuit properties, they worked in the other place, they didn't damaged cable, they only caused few seconds synchronization break (my and probably other people synchronization because immediately after reconnecting I've had smaller about 1 dB smaller SNR margin than target SNR margin). They worked in the place slightly after my home, after my cabinet. They worked in the place where the phone cable is very deep (too deep to damage it by heavy equipment but perhaps they caused shock). Perhaps it was accidence. Perhaps that day my ISP has doing something in the central office and temporary switched something and next day switched again. Next day after that day I've had reconnection again (also when pavement works had place) and the same Hlog as the days before that day. I've had temporary one day other Hlog than usual despite that day own reconnections

I believe that some damage was caused to the cable by the pavement works?

It isn't. They probably reconnected something.

As I have said before, it is a very difficult task (almost impossible) to remotely diagnose potential faults in a circuit. It really requires someone to physically attach various items of test equipment and make measurements.

What could I do? I'm very curious. It is very curious anomaly.

Is the first black cable thicker (first photo) than second black cable (second photo)? They should be the same cable. But I can't exclude that there are two sections to the external cabinet.



Best regards
konrado5