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Author Topic: Shunt fault?  (Read 3316 times)

konrado5

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Re: Shunt fault?
« Reply #15 on: July 30, 2016, 12:24:45 PM »

I correct my observations. It is difficult to abstract from measurement errors. It seems that on usual Hlog I have too much attenuation on tones 33-100 (unknown minimum because of measurement errors) and 170-220 (210 is minimum). On abnormal Hlog I have too much attenuation on upstream, 120-170 (150 is minimum). Perhaps I have bridge tap on circuit and pavement workers changed the bridge tap parameters? Could you look at this graph and estimate if 210 dip indicate bridge tap? The 55 dip is measurement error. It is curious that on both Hlogs (first post in this thread) there is almost the same attenuation on 250-511 tones. It weights in favour of bridge tap hypothesis because HR joints and capacitive faults affect the whole ADSL band but in the different degree. Admittedly HR joint causes higher attenuation especially in low frequiences but higher frequiences are also affected. Bridge taps affect selectively.

Best regards
konrado5
« Last Edit: July 30, 2016, 03:00:22 PM by konrado5 »
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burakkucat

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Re: Shunt fault?
« Reply #16 on: July 30, 2016, 04:00:24 PM »

Could you look at this graph and estimate if 210 dip indicate bridge tap?

I have looked and it is exactly as what I have previously seen in some of your Hlog plots. It is not due to a bridging tap. Its shape is quite wrong; it is too wide and shallow.

I attach, below, two Hlog plots with data obtained from one circuit. (Unfortunately the CPE - DSLAM paring did not record the US data. (Upstream relative to the CPE.)) The first plot shows the presence of a bridging tap. The second plot is from the same circuit once the bridging tap had been removed.

The third image, attached for reference, shows the classic shape which is characteristic of a bridging tap.
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konrado5

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Re: Shunt fault?
« Reply #17 on: July 30, 2016, 04:45:42 PM »

On attached j3w9khlog you found bridge tap. But it seems to me that it has similar depth and wideness.
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burakkucat

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Re: Shunt fault?
« Reply #18 on: July 30, 2016, 05:18:22 PM »

On attached j3w9khlog you found bridge tap.

Correct. Look at the first minimum, at the low frequency end of the plot. Look at its shape. That is exactly what I would expect. Granted there is some distortion in the plot. But not everything in this world exists in an "either or" binary state. There are varying degrees in between. Experience tells me that the initial minimum, at around sub-carrier 60, is due to the presence of a bridging tap. The subsequent minima, as one views the plot in a low frequency to high frequency direction, become both less deep and wider. That is expected. They are the harmonic responses of the original response. It is by consideration of the initial and the subsequent harmonic minima that allows one to estimate the approximate length of the bridging tap. (Note the words "estimate" and "approximate" are used.) Experience tells me that the circuit, from whose data that the "j3w9khlog" plot was generated, had a bridging tap at the time the data was collected.

Quote
But it seems to me that it has similar depth and wideness.

In your opinion.

I have nothing more to add to this thread. It has deviated away from its original topic of "Shunt fault?" and has become an irritating distraction that has consumed a significant amount of my time.
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konrado5

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Re: Shunt fault?
« Reply #19 on: August 02, 2016, 03:50:59 PM »

burakkucat: Little misundestanding again. I don't think that minimum on my 210 tone is the real first minimum. I think the first minimum is somwhere at the tones 33-50 or upstream. It is difficult to estimate because on these tones there are significant measurement errors, for example minimum at tone 55 is caused by Annex M PSD mask. G.922.3 suggests that on tones 33-45 it is possible that there are inaccurate measurements.
Quote
The accuracy requirements for the downstream HLOGps (HLOGps_ds) shall apply only to the
following subcarriers (with the corresponding frequency ranges being a part of the passband), and
only if not within the downstream BLACKOUTset (see clause 8.13.2.4):

Annexes A and I:
Subcarriers 46 to 208.
« Last Edit: August 02, 2016, 03:55:35 PM by konrado5 »
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William Grimsley

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Re: Shunt fault?
« Reply #20 on: August 02, 2016, 03:56:59 PM »

konrado5, burakkucat has said that he doesn't want to add anything more to the thread. Jeeez. ::)
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konrado5

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Re: Shunt fault?
« Reply #21 on: August 02, 2016, 04:04:17 PM »

But I had to add. Sorry.
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konrado5

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Re: Shunt fault?
« Reply #22 on: August 02, 2016, 04:13:50 PM »

Now I agree with old burakkucat statement.
Quote from: burakkucat
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.
http://forum.kitz.co.uk/index.php/topic,14437.msg270696.html#msg270696
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William Grimsley

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Re: Shunt fault?
« Reply #23 on: August 02, 2016, 04:15:15 PM »

It's fine, mate. We're just chilling on here, you know? :)

Meant to ask, what's my Hlog and QLN looking like? MDWS ID is WilliamG.
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konrado5

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Re: Shunt fault?
« Reply #24 on: August 02, 2016, 04:27:23 PM »

Your Hlog is perfect. On QLN I see the radio frequency ingress on tones 211-244 (frequiences about 900-1050 kHz).
It should be helpful
" ~ Medium Wave Channels in the UK that may interfere with broadband"
http://www.kitz.co.uk/adsl/rein.htm
« Last Edit: August 02, 2016, 04:30:09 PM by konrado5 »
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William Grimsley

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Re: Shunt fault?
« Reply #25 on: August 02, 2016, 05:07:09 PM »

That's great. Thanks for the information.
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konrado5

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Re: Shunt fault?
« Reply #26 on: December 30, 2016, 04:41:25 PM »

I think that burakkucat misunderstood what I've tried to convey. Look again at Double_Hlog1.png. The green graph is anomalous Hlog (when pavement works caused disconnection). It is noticable that lazy roll around 210 tone was moved to 150 tone. I think it is harmonic response on the first minima (on the red graph 33-90 tones, on the green graph somewhere on upstream, upstream don't measured unfortunately). Moreover, I don't think that 55 minima is real bridge tap minima. It is measurement error. On the Double_Hlog2.png this minima is lesser on the green graph (anomalous synchronization with 15 dB target SNR margin).
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konrado5

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Re: Shunt fault?
« Reply #27 on: August 14, 2017, 10:36:50 PM »

burakkucat: do you think it is possible that lazy roll is harmonic response to first minima?
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j0hn

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Re: Shunt fault?
« Reply #28 on: August 14, 2017, 11:51:59 PM »

Quote from: burakkucat
I have nothing more to add to this thread. It has deviated away from its original topic of "Shunt fault?" and has become an irritating distraction that has consumed a significant amount of my time.
:whistle:
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