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Subject - ADSL telephone line Can anybody help me with a...

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Question by Shaun
Submitted on 12/30/2003
Related FAQ: N/A
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Subject - ADSL telephone line
Can anybody help me with a internal telephone line problem which affects my adsl modem? I have 5 extension sockets all hardwired internally and suffer from constant disconnection of the adsl service. If I have the modem plugged into the BT socket with all extensions disconnected; there are no disconnections of the service. I have also discovered that in the modem diagnostics program, under ADSL Tab; when connected only to the first point into the house, there are no 'loss of framing', 'loss of signal' or 'errored seconds' but with the other extensions connected, the ADSL diagnostic chart shows rising numbers in the loss of framing, signal and errored seconds whilst connected.

Whilst having the extensions disconnected I have tested my extension cable with an insulation resistance tester and an ohm meter to check continuity of all pairs which all tested ok but I have found that the cable has what I think is an induced voltage of 12 volts measured to earth. I am now sure this is what is causing my adsl modem to disconnect.

The house extension sockets are wired in standard 3 pair cable and assume the induced voltage is being caused from mains electric cables within the house.

I wasn't to bothered about having all the points in the house but needed just one elsewhere so I decided to wire an extra point in CAT5 UTP data cable from my first point and clipped it well away from any mains cables through the loft and down the cavity in flexible conduit to the other point and connected it up.

Would you believe I still had the disconnections and the diagnostics of framing, signal and errored seconds were rising once again. I once again disconnected this cable and measured between each core and earth and had 12 volts again. I then wanted to prove that the induced voltage was from my house so I switched the main switch off at the distribution board and measured the cable again, 0 volts, switched it on again, 12 volts. I have tried isolating each circuit in turn but it doesn't go.

Does anybody know of anything I can do to solve this problem. Would having screened or foiled cable help? I don't want to spend money on expensive cable and find it still has this induced voltage. I thought that having CAT 5 cable being twisted pairs should give a balanced circuit and leaving them twisted right up to the connection.

Any help on what can be done or any information on EMI or be directed to other discussion groups would be much appreciated.



Answer by Akilia
Submitted on 8/23/2004
Rating: Not yet rated Rate this answer: Vote
Good question, I don't know if anyone has answered it. I am having the same problem.

Firstly, if you want to install a screened cat5e cable, it will not show benefit if you connect it into the wiring network which is already demonstrably acting as an aerial. You would have to disconnect the remaining internal network, or install a second telephone line specifically for broadband. The Filter Splitters allowing telephones and ADSL to be used simultaneously on the same telephone copper wires do not necessarily filter out aerial interference, only separate out the voice range (for speech and dial-up connections, fax etc) from the ADSL frequencies.

In actual fact, the BT standard for ADSL internal cabling is CW1308 TP (twisted pair). It is possible that your existing wiring is not up to that standard, whereas your new cable exceeds that if it is Cat5e FTP (Foil screened twisted pair) - and is probably fatter.

My cabling is CW1308 TP, I am wondering if I need to use CW1308 FTP, because I can't surface-mount the fat cat56e able without serious aesthetic penalty points.

Anyone else got any thoughts?
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