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Uber Geek
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Topic # 28624 6-Dec-2008 12:10
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From the thread that just got locked

"the easy way to tell your distance from the exchange is to find your downstream line attenuation and divide by 13.8 it gives your distance as 3.2 km, mine is 54db so divide by 13.8 and my distance is 3.9 km"

Based in this formula I'm 3.2 KM from Papatoetoe in Auckland.  I get  5~6Mbits on the speed test.  Is that good for 3.2Km on ADSL2??





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  Reply # 182468 6-Dec-2008 12:42
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  Reply # 182655 8-Dec-2008 02:29
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distance is but 1 thing to take into account there's also line noise and age of the phone lines that connect you to your exchange

ie; i have 50db att / 13.8 = 3.6KMs which when looking at the chart it estimates i should be getting around 5.5Mbps
but my lines are 35 ~ 40 yrs old and can be quite noisy ( SNR= 3 ~ 12db) at times so im only getting 2.24Mbps down and 672Kbps up do see where im going here Distance isn't always the only factor but it can certainly help to be closer

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Master Geek

  Reply # 182820 8-Dec-2008 18:35
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I have the same issue.

I manually checked my distance from the exchange with online maps and I got 3.4km distance.
I also did the divide anttuation by 13.8 and I get 3. something km so it seems roughly accurate.

According to that chart, at the 46.2Db I currently recieve I should be getting close to 8mb sync, I only get half of that, so I assume my 30 year old house has something to do with that. My SNR also varies, goes as low as 4 and as high as 8

On the side of my house, there is a small sign against the wall stating the telephone cables under the sign belonged to the post this house is old, pre-telecom old.

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Ultimate Geek
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  Reply # 182868 8-Dec-2008 22:24
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You might be able to improve things by tidying up the house wiring.  We had all sorts of problems getting broadband to work in our 90 year old villa, and a very nice man from Telecom spent an hour converting our jack points to 2-wire and running a new cable through the roof to the phone cable.  And we weren't even paying for wiring maintenance!

If the phone wiring in your house is not 100%, installing a splitter can also help.

I was a geek before the word was invented!

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Ultimate Geek
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  Reply # 186920 1-Jan-2009 17:15
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The formula "distance (km) = attenuation/13.8" is probably reasonable for most Orcon customers who will be in urban areas with 0.4mm feeder cable. Probably not so accurate as Orcon get closer to the edge of town and start to connect rural people who will be on 0.63mm cable.

In my case (urban) about 39db / 13.8 = 2.8 km which seems a bit longer than the shortest path by road, but of course the Telecom cable architecture doesn't always follow the shortest path as the larger feeder cables will tend to follow the main roads, not the shortest path to your front door.

So from the chart, while I'd probably get a small improvement from upgrading from my old ADSL(1) router, it's going to be less than 10Mbps.

w2krules mentioned splitters - did anyone here who rewired their home with a splitter and 2-wire cabling notice a lower attenuation figure, or just an improvement in x-talk and noise resulting in improved speed?

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Ultimate Geek
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  Reply # 187149 3-Jan-2009 12:40
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alexx: In my case (urban) about 39db / 13.8 = 2.8 km which seems a bit longer than the shortest path by road, but of course the Telecom cable architecture doesn't always follow the shortest path as the larger feeder cables will tend to follow the main roads, not the shortest path to your front door.

Interesting - if I use google maps to plot the most likely cable route along the main roads (not the shortest route), then I get about 2.1 km.

So according to the formula: attenuation = 2.1 km x 13.8 = 29db.

In practice:

M11> show dsl
DSL Statistics:
     Type               : ALC MULTI-MODE CP
     Datapump HW Rev    : ff
     Datapump FW Rev    : 1.6.25
     Datapump Vendor ID : ffff
     Current Status     : LINK UP
     Operating Mode     : G.DMT
     Data Path          : Interleave
                           Downstream    Upstream
     Current Rate  :          7520 Kbps      992 Kbps
     Maximum Rate  :          7595 Kbps      992 Kbps
     Noise Margin  :           3.5 dB        9.0 dB
     Attenuation   :          39.0 dB       23.5 dB
     Out Power     :          19.5 dB       12.0 dB

                                     Near        Far
     FEC Counts Interleave :       21557          45   
     CRC Counts Interleave :        1193           9   
     HEC Counts Interleave :         929           6   

So 39db (actual) vs. 29db from a conservitave distance estimate.
Perhaps not surprising as there might be some old cable in this part of town.

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