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Author Topic: Finding line length on FTTC  (Read 632 times)

michty_me

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Finding line length on FTTC
« on: October 19, 2018, 10:14:23 AM »

I know on ADSL it was a bit easier to have a more educated guess on your line length by looking at the stats.
Is there any way to get a fairly accurate line length estimate from your house to the cab or is it a case of using Google maps to plot a possible route and hope for the best? I seem to remember people saying using the attenuation didn't work as well on FTTC.
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dee.jay

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Re: Finding line length on FTTC
« Reply #1 on: October 19, 2018, 12:09:48 PM »

You can use the Google maps method, but that is only as good as "the crow flies"

I always assumed my line length was 500m using the above method, but it turns out, I am actually 600m in real distance because the underground distribution point for my street runs past my house, so I'm 50m in the wrong direction to start with!

So it may be a case of having to do some investigation out in the street as well. All depends how your lines are routed of course. Some lines are on telegraph poles of course, so much easier to see where they go.
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4candles

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Re: Finding line length on FTTC
« Reply #2 on: October 19, 2018, 02:07:29 PM »

You can use the Google maps method, but that is only as good as "the crow flies"
Right click on a location and select "Measure distance". Left click on another location and you'll get the straight line distance.
Now hover anywhere on the line, and you can move it bit by bit so that you can follow the curves and corners in the road(s).
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dee.jay

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Re: Finding line length on FTTC
« Reply #3 on: October 19, 2018, 02:08:52 PM »

Right click on a location and select "Measure distance". Left click on another location and you'll get the straight line distance.
Now hover anywhere on the line, and you can move it bit by bit so that you can follow the curves and corners in the road(s).

A very good point - I somewhat failed to highlight that. One still needs to work out where the wires go first, though :)
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michty_me

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Re: Finding line length on FTTC
« Reply #4 on: October 20, 2018, 12:42:17 PM »

So using the method above and depending which entrance the PCP takes into my street, my line length is either roughly 490m or 330m give or take. Pity as I can see it from my window and a straight line measurement is 55m or so.
Reason I was asking was g.fast pods started appearing in surrounding areas so I was wanting to see if it was worth while getting my hopes up. I guess not  :lol:
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re0

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Re: Finding line length on FTTC
« Reply #5 on: October 20, 2018, 04:42:50 PM »

I seem to remember people saying using the attenuation didn't work as well on FTTC.
You can use attenuation to a degree, I think. It's not really so much different than ADSLx in the respect that knowing the actual length is of course the best but the attenuated figure is probably your best bet if you do not know the exact route and therefore length. I did some calculations and my line length came back as about 190m or something, though that is the attenuated length based on 0.4mm copper as reference I believe and certainly not the actual (though the actual is most likely a couple of tens of meters shorter).

I have no recollection of what equation I used to get that figure though. ;D
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michty_me

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Re: Finding line length on FTTC
« Reply #6 on: October 22, 2018, 10:24:12 AM »

You can use attenuation to a degree, I think. It's not really so much different than ADSLx in the respect that knowing the actual length is of course the best but the attenuated figure is probably your best bet if you do not know the exact route and therefore length. I did some calculations and my line length came back as about 190m or something, though that is the attenuated length based on 0.4mm copper as reference I believe and certainly not the actual (though the actual is most likely a couple of tens of meters shorter).

I have no recollection of what equation I used to get that figure though. ;D

If you do remember your equation, It would be handy to know!!
I've just checked my attenuation figures and it seems to be around 17.5dB
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j0hn

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Re: Finding line length on FTTC
« Reply #7 on: October 22, 2018, 10:52:41 AM »

AIUI majority of D-Side copper is 0.5mm so an equation/algorithm that works out line length from attenuation based on 0.4mm copper would only help if you know your local d-side is 0.4mm.

I'd guess re0 has 0.4mm on his d-side but it's all 0.5mm in my area.
Any aluminium on the line would throw the results off also.
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michty_me

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Re: Finding line length on FTTC
« Reply #8 on: October 22, 2018, 11:06:31 AM »

AIUI majority of D-Side copper is 0.5mm so an equation/algorithm that works out line length from attenuation based on 0.4mm copper would only help if you know your local d-side is 0.4mm.

I'd guess re0 has 0.4mm on his d-side but it's all 0.5mm in my area.
Any aluminium on the line would throw the results off also.

That's handy to know John, thanks.
I'm not too sure about my d-side but I'm fairly certain there is no aluminium.
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roseway

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Re: Finding line length on FTTC
« Reply #9 on: October 22, 2018, 11:48:16 AM »

Don't forget that there's more to it than just the resistance of the cable. We're dealing with high frequencies, and so inductive and capacitive effects and skin effect come into play. These will vary from line to line, so any calculation of line length based on attenuation can only be an approximation.

Some years ago, when connections were being upgraded from ADSL to ADSL2+, which doubled the tone range used by the connection, it was commonly noticed that modems reported an attenuation which was ~3 dB higher than before. With VDSL2 the tone range is much greater, and more variable, so the frequency effects on attenuation will be correspondingly higher.
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  Eric

re0

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Re: Finding line length on FTTC
« Reply #10 on: October 24, 2018, 12:39:51 AM »

I have a feeling I initially did it in an unscientific manner, which would not be much use to people here. :no:

Unfortunately, I do not know how loop loss increases over distance. Anyone with this information to hand may be able to work out what gauge of cabling they are on by characteristics of their line, but there is always going to be the issue that different legs can be using different gauges and materials so you can only be so accurate.

They way I remember people estimating distance with attenuation on ADSLx was to do [attenuation@300 kHz]/[cable loss dB/km]. Differently gauges and their repsective losses can be found here. I did mine (FTTC) on Tone 70 (301.875 kHz) since it's the closest to 300 kHz and got a value of 0.19 km, which is probably a little bit longer than actual length since I am pretty sure I have 0.4mm copper and/or aluminium.

In the end, this is just an approximation.
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