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Author Topic: REIN REIN, go to Spain...  (Read 5869 times)

boozy

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Re: REIN REIN, go to Spain...
« Reply #30 on: June 02, 2018, 01:54:17 PM »

For a bridged tap length calculation (I wrote that code before to figure out my tap - gave 77m, so seems to be good enough):

tones is the number of tones between troughs and dips are the number of troughs across the measurement (2 if you measure two adjacent troughs)

Code: [Select]
            lengths  = new double[16,5] { { 100, 231.9, 463.8, 695.7, 927.5},
                { 150, 154.6, 309.2, 463.8, 618.4},
                { 200, 115.9, 231.9, 347.8, 463.8},
                { 250, 92.8, 185.5, 278.3, 371.0},
                { 300, 77.3, 154.6, 231.9, 309.2},
                { 350, 66.3, 132.5, 198.8, 265.0},
                { 400, 58.0, 115.9, 173.9, 231.9},
                { 450, 51.5, 103.1, 154.6, 206.1},
                { 500, 46.4, 92.8, 139.1, 185.5},
                { 550, 42.2, 84.3, 126.5, 168.6},
                { 600, 38.6, 77.3, 115.9, 154.6},
                { 650, 35.7, 71.3, 107.0, 142.7},
                { 700, 33.1, 66.3, 99.4, 132.5},
                { 750, 30.9, 61.8, 92.8, 123.7},
                { 800, 29.0, 58.0, 87.0, 115.9},
                { 850, 27.3, 54.6, 81.8, 109.1}
                    };

        private double TonesToLength(int tones, int dips)
        {
            if (tones > 850 && dips>2)
            {
                tones = tones / (dips - 1);
                dips = 2;

            }
            double ret=0.0;
            int i = 0;
            while (lengths[i, 0] < tones)
            {
                i++;
            }
            //assume each is straight
            if (i == 0)
                ret = 300.0;
            else
            {
                if (dips ==1)
                {
                    ret = 0.0;
                }
                else
                {
                    dips = dips - 1;
                    double aboveprev = tones - lengths[i - 1, 0];
                    double betweenTones = lengths[i , 0] - lengths[i - 1, 0];
                    ret = lengths[i - 1, dips] + (lengths[i, dips] - lengths[i - 1, dips]) * (aboveprev / betweenTones);
                }
            }
            return ret;
        }


being dragged to the shops - but I'll stick in the figures when I'm back and could tell what length a tap would need to be to cause that periodicity.

Edit: kids weren't ready...  if it's a bridged tap, it's about 92m long (254 tone period)
« Last Edit: June 02, 2018, 02:05:39 PM by boozy »
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tickmike

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Re: REIN REIN, go to Spain...
« Reply #31 on: June 02, 2018, 02:59:29 PM »

Sometimes it's good to talk - I was just asking one of the neighbours if they have anything on a timer starting at 7pm.  They hadn't but they do lose their internet connection and sometimes electricity at 7pm.  It's not bothering him overly as it's a business and he has some guard dogs so the security cameras aren't that important, but it is annoying him a bit.

I'm guessing he's nearer the source than me, so I will go down there this evening.

I had problems with REIN a few years ago, after weeks and weeks interference that only came on when it got dark and off when it got light, A 'OR' engineer found it was a distant neighbours Security cameras power supply units.
There very long phone drop wire was re-radiating the interference all down our lane.
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Weaver

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Re: REIN REIN, go to Spain...
« Reply #32 on: June 02, 2018, 04:47:38 PM »

If this helps:

Relating to that link I posted to a possible situation here: the reflected signal comes back and interferes with the original, and the superposition gives cancellation or reinforcement in a frequency-dependent way. This is exactly the same thing as the pattern of colours seen on a very thin oil film sheen on a pool of water, because of reflected light from both the top and bottom surfaces of the oil, two light waves combine together with a result depending on the exact thickness of the oil film.

The e-iωt gives the sinusoidal variation with frequency ω, and the time delay t controls the width in frequency-space of the distance between peaks in the frequency-spectrum sinusoidal pattern.
« Last Edit: June 06, 2018, 03:16:23 AM by Weaver »
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burakkucat

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Re: REIN REIN, go to Spain...
« Reply #33 on: June 02, 2018, 05:00:16 PM »

Is a bridged tap a source of reflections?

Indeed it is.

What we have to remember is that the original telephony circuit has been cajoled into acting as a radio frequency transmission line (or feeder), operating in differential mode.
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ejs

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Re: REIN REIN, go to Spain...
« Reply #34 on: June 02, 2018, 05:03:31 PM »

Which part of the HLog graph in the first post are people getting a bridged tap from? I thought it looked pretty much fine.
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burakkucat

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Re: REIN REIN, go to Spain...
« Reply #35 on: June 02, 2018, 05:07:42 PM »

Which part of the HLog graph in the first post are people getting a bridged tap from?

I'm not.  :no:

Quote
I thought it looked pretty much fine.

Agreed.

It is the QLN plot that has an underlying sinusoidal background which becomes visible at the higher frequencies. (Reply #6.)

My later post (Reply #26) is probably the source of the confusion.
« Last Edit: June 02, 2018, 05:22:28 PM by burakkucat »
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ejs

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Re: REIN REIN, go to Spain...
« Reply #36 on: June 02, 2018, 05:30:10 PM »

Isn't that shape of the QLN merely indicative of crosstalk from other VDSL2 lines?
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burakkucat

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Re: REIN REIN, go to Spain...
« Reply #37 on: June 02, 2018, 05:33:22 PM »

I'm not sure.  :shrug2:  Would you be able to convince me, please?
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ejs

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Re: REIN REIN, go to Spain...
« Reply #38 on: June 02, 2018, 05:46:21 PM »

kitz mentioned spotting crosstalk from QLN or bitloading:
https://forum.kitz.co.uk/index.php/topic,20906.msg363413.html#msg363413
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Weaver

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Re: REIN REIN, go to Spain...
« Reply #39 on: June 02, 2018, 06:28:01 PM »

I don't see that there would be a relative time delay between disturbers in crosstalk?

I see which graph Burakkucat was looking at, mea culpa, I was looking at the wrong one and was confused probably just as ejs was. The pattern is very clear there.
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burakkucat

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Re: REIN REIN, go to Spain...
« Reply #40 on: June 02, 2018, 06:33:53 PM »

kitz mentioned spotting crosstalk from QLN or bitloading:
https://forum.kitz.co.uk/index.php/topic,20906.msg363413.html#msg363413

Hmm . . . I remember that post, now that you have pointed me in its direction.
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Weaver

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Re: REIN REIN, go to Spain...
« Reply #41 on: June 02, 2018, 07:23:21 PM »

Reading it off the right graph now, I make the period about 220 tones. So assuming the speed of light in copper is c, the in-vacuo speed, which it isnít, but anyway, my calculator says the reflection round trip length would be 316 m, so 158 m length one-way.

Would someone check my arithmetic?

But that needs to be corrected according to whatever the propagation speed really is. Using a velocity factor of 0.67 for copper then that would make the length about 106 m (again one-way length, not round trip). But someone who knows about TDR would know the correct numbers.
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ejs

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Re: REIN REIN, go to Spain...
« Reply #42 on: June 02, 2018, 07:35:27 PM »

It's not the arithmetic that needs checking! There's nothing on the HLog graph, and you shouldn't be trying to calculate bridge tap lengths off a QLN graph.
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boozy

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Re: REIN REIN, go to Spain...
« Reply #43 on: June 02, 2018, 08:15:59 PM »

I've been reading...  would a more accurate term be impedance mismatch rather than bridged tap (this may be totally wrong, as I still don't know much about the domain).  Wouldn't that look like the graph (as opposed to crosstalk which would look like the middle of an "m", can't think of another letter with 2 curves meeting in a point).

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burakkucat

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Re: REIN REIN, go to Spain...
« Reply #44 on: June 02, 2018, 09:39:42 PM »

I've been reading...  would a more accurate term be impedance mismatch rather than bridged tap (this may be totally wrong, as I still don't know much about the domain).  Wouldn't that look like the graph (as opposed to crosstalk which would look like the middle of an "m", can't think of another letter with 2 curves meeting in a point).

I have collected together some example plots for you and have sent you a PM.
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