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Author Topic: About my possible bridge tap issue  (Read 18837 times)

burakkucat

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Re: About my possible bridge tap issue
« Reply #45 on: December 05, 2015, 04:59:21 PM »

I'm not sure you should be converting from 68m to 680m.

My calculations have subsequently been revised to account for the twelfth dip that is present in gazaai's Hlog plot.

The two figures (corresponding to those above) are now seen to be 67.6 and 744 metres.
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WWWombat

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Re: About my possible bridge tap issue
« Reply #46 on: December 05, 2015, 08:00:14 PM »

Here is the link to the alternative calculation method I mentioned in my earlier post:
http://www.elnex.pl/product/attachment/d096f15ee037f5f693e1f7867366a54a/pl_PL/Analiza-petli-abonenckiej-SmartClass-TPS.pdf

The description is on the bottom of page 1, and top of page 2.
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burakkucat

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Re: About my possible bridge tap issue
« Reply #47 on: December 05, 2015, 08:18:58 PM »

Here is the link to the alternative calculation method I mentioned . . .

Thank you. I shall read it with interest.
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WWWombat

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Re: About my possible bridge tap issue
« Reply #48 on: December 05, 2015, 08:28:00 PM »

Here is a link to *another* document which mentions bridge taps, but this one has a couple of decent examples:
https://www.broadband-forum.org/technical/download/TR-197.pdf

This document is TR-197 from the Broadband Forum, discussing DSL quality factors. The relevant section is on "dual-ended line tests" that are performed in some DSL modems.

Figure 10, page 51, shows the Hlog for a line in 3 states:
- Perfectly normal
- With a 30m bridge tap, first dip somewhere around tone 520. We get to see one further dip.
- With a 200m bridge tap, first dip somewhere around tone 55. We get to see 13 further dips.

Sanity check of the previous formula:
- Tone 520 = 2.25MHz. Tap length = (160 2.25) ft = 71 ft = 22m.
- Tone 55 = 0.24MHz. Tap length = (160 0.24) ft = 667 ft = 203m

The sanity check isn't far off, telling us the formula is a reasonable estimate. In that case, we just measure the first dip, and ignore all the rest.

With gazaai's first dip occuring at tone 164, I calculate:
- Tone 164 = 0.71MHz. Tap length = (160 0.71) ft = 225 ft = 69m

I think that gives us the answer for the total tap length.

That backs up (nearly) just reading data from table 2 (in the original JDSU document) as the only step needed. I don't think you need to perform averages over the extra dips (except for the fact it might give you a better accuracy for where the first dip really was), nor to multiply by the number of visible dips (after all, in reality, those dips go on ad-infinitum).

I also think I know how to read the example in that 1st document better now ... but I'll have to do that in a separate post, likely tomorrow.
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burakkucat

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Re: About my possible bridge tap issue
« Reply #49 on: December 05, 2015, 11:31:10 PM »

Having carefully re-read the original document, and with some help from WWWombat, I now can see that I was caterwauling nonsense.  :-[

The first table shown in Reply #16 is good. The nonsense follows on from that table.

I now present my correction by beginning with a reworking of the original good table --

Code: [Select]
Index Tones at Minima Use as Midpoint Delta from No. of Intervening
----- --------------- --------------- Index 1 Minima from Index 1
---------- -------------------

  1    160 -  167       163.5       0   -
  2    496 -  503       499.5     336   0
  3    832 -  839       835.5     672   1
  4   1144 - 1151      1147.5     984   2
  5   1512 - 1519      1515.5    1352   3
  6   1848 - 1855      1851.5    1688   4
  7   2192 - 2207      2199.5    2036   5
  8   2528 - 2535      2531.5    2368   6
  9   2864 - 2887      2873.5    2710   7
 10   3208 - 3215      3211.5    3048   8
 11   3552 - 3567      3559.5    3396   9
 12   3936 - 3943      3939.5    3776 10

We should now look at columns four and five of the above table and cross-reference the second, third and fourth entries with Table 2 (of the PDF document, as referenced in my initial post).

By simple algebra, we can see that the second, third and fourth entries of columns four and five of my table, immediately above, give values of 69.0 metres, 69.1 metres and 70.7 metres for the length of the bridging tap.

Taking the average of those three values gives 69.6 metres as the approximate length.

We are now left with just one unknown: the location of the start of the bridging tap with reference to a known point in the circuit. That can be determined by TDR measurements from the NTE5/A looking towards the PCP and also from the PCP looking towards the NTE5/A, as it is highly likely that the tap is somewhere within the D-side. (b*cat nods towards B*Sheep;)  )

Team-work prevails, once again.  :)



So that all the information is contained within one place, I attach two extracts, below, from the Broadband Forum's document TR-197 that WWWombat referenced in his preceding post.
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gazaai

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Re: About my possible bridge tap issue
« Reply #50 on: January 04, 2016, 03:54:32 PM »

Small update on this. An engineer was out on 31st of December, I told him about a possible bridge tap issue and showed him a few graphs etc. He told me he wasn't interested and looked straight into the wiring. He seemed pretty annoyed that I called an engineer out when I am receiving 65mb and wasn't in the best of mood to begin with lol.

He had a look at the line with his device and done several tests. On one test he told me there is some sort of issue with the line outside my house around 70 metres away. When I looked at the screen it seemed to be a small graph with a straight line then a spike in the centre, I didn't get a good enough look. So I don't know what this test actually shows.

He was surprised at the length of span between my house and the pole, with a guess I would say around 50 metres to 60 metres going by several houses and at one point it dips so low the neighbour can almost touch it while outside his back door.

Well he then went on to say it was too dark to do anything else at the time, it was 5pm and pitch black. So he said he would leave the case open and another engineer would come out possibly on the 2nd or 3rd to have a look at the cable. I'm not to sure what to think as on the BT Faults page it says my fault should be fixed and I haven't received any texts or calls from Openreach so I am wondering if the case has been closed.

Ill update further on this if an engineer comes out again.
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burakkucat

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Re: About my possible bridge tap issue
« Reply #51 on: January 04, 2016, 06:02:13 PM »

Hmm . . . Interesting.  :-\

Please do keep us updated.
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gazaai

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Re: About my possible bridge tap issue
« Reply #52 on: January 06, 2016, 02:48:25 PM »

I got in contact with the engineer again over the phone. He says its been cleared on his notes and the fault has been proven to be outside. He said there is no need for another engineer to come out to my home. He says an engineer will come out and fix the fault outside themselves. Does anyone have past experience with this as it will be 1 week tomorrow with nothing being done?
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NewtronStar

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Re: About my possible bridge tap issue
« Reply #53 on: January 06, 2016, 09:24:32 PM »

He says an engineer will come out and fix the fault outside themselves. Does anyone have past experience with this as it will be 1 week tomorrow with nothing being done?

You have to see this as good result a fault has been found on your circuit so it needs more man power to fix this dropwire issue if it is as low as you say then either a second distribution pole will need to be erected to combat the effects of gravity on the dropwire joints.

Though my dropwire cable is 41 meters in length so it's not that bad if i was an OR engineer i would go to the tension bar at the house and make adjustments until the dropwire is higher up in the air
« Last Edit: January 06, 2016, 09:47:16 PM by NewtronStar »
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Black Sheep

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Re: About my possible bridge tap issue
« Reply #54 on: January 06, 2016, 09:41:39 PM »

For info: 68mtrs is the maximum span between poles, or pole to house, on non-aerial cable. The 'spike' he could see is most likely a HR fault.

Without pictures and true distances, the rest is guesswork. :)
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burakkucat

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Re: About my possible bridge tap issue
« Reply #55 on: January 06, 2016, 10:55:03 PM »

. . . a second distribution pole will need to be erected . . .

[Terminology / Jargon}: The second pole in such a situation would be called a "carrier pole".

Our very own Bald Eagle1's aerial service feed begins at a pole-top DP on the far side of a major road. It crosses the road to a carrier pole (thus maintaining adequate clearance above the road's surface) and then drops down to the side of the building.  :)
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burakkucat

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Re: About my possible bridge tap issue
« Reply #56 on: January 06, 2016, 10:57:28 PM »

For info: 68mtrs is the maximum span between poles, or pole to house, on non-aerial cable.

Thank you. I knew that there is a defined maximum span length but I could not recall the actual value.
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gazaai

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Re: About my possible bridge tap issue
« Reply #57 on: January 07, 2016, 10:48:40 AM »

Well guys its been fixed  :D and the issue was pretty simple yet out of my control. It turns out that the two pairs were joined together at the pole. Orange and white connected together with the green and black. The engineer said he hasn't seen that before.

Well you can see my before and after on MyDSLWebStats, username: GaZaai.

Thanks for your help :)
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Black Sheep

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Re: About my possible bridge tap issue
« Reply #58 on: January 07, 2016, 11:34:40 AM »

Result.  :) :)

I have to say though, I'm incredibly impressed with W3 and B*Cats scientific approach and calculating the length of the bridged-tap .............. absolutely spot-on at 69/70mtrs from the NTE.  :graduate:
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gazaai

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Re: About my possible bridge tap issue
« Reply #59 on: January 07, 2016, 04:53:22 PM »

Yeah that was great work, it was excellent help. Here is some before and after shots:

Attenuation:


HLog:


Sync Rate:
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