Extending BT's telephone cable for broadband

  JOHNKM 10:34 04 May 05
Locked

I have just gone on to Tiscali’s 256K broadband (I thought that I was playing it safe, as my line is not suitable for anything faster than 512K). This works OK using a laptop/modem directly connected (via the filter) to the BT master socket, but I am having problems with connecting to the main computer, which is 20m away.
I am an Electronics Engineer and aware that normal telephone extension cable will not work, but have also been told that RJ11 cable cannot be used at lengths >10m, without compromising connection speed. As I have a large quantity of ‘CAT 5’ networking cable, I tried a 20m length of this, which works OK, giving the correct connection speed of 589.8 kps (the same as the laptop directly connected to the BT socket). However, any (dc type) disturbance on the telephone line, such as, when picking up the phone to make a call, or putting it down at the end of a call, will cause the modem to lose ADSL lock. It may then relock while the call is in progress, only to drop out again when the phone is put down.
The BT cable has already run well over 300m from the roadside box, so I would not have thought another 20m going to make any difference, provided the cable has similar characteristics (e.g. with matching impedance's, capacitance, etc). Therefore, as this oddity does not occur with the laptop set up, I assume there may still be a cable mismatch.
So, does anyone know the spec of BT’s external cable, or could this ADSL lock drop-out be due to another reason? I have found both Tiscali, and BT, unable (or unwilling) to answer the simple question on cable spec. They can only suggest moving my computer closer to the BT socket, or have BT install (at great expense) an extension cable from the master socket.

  TonyM 14:31 04 May 05

You say "normal telephone extension cable will not work" .....why is that ?

I ran an ordinary piece of telephone extension wire myself from my BT main socket to a socket screwed in my upstairs study, and my broadband modem is connected through that with no problem whatsoever (on freeserve 1meg service, and with another desktop and up to 3 wireless laptops sharing the connection !)

Cost was about £4.99 at Maplin I think, for 15m of cable and an extension socket..

  JOHNKM 15:09 04 May 05

This type of cable is lossy, not being of twisted pair construction and is a known problem area with broadband connection difficulties, particularly with long extension cable lengths and/or a long BT run to the exchange.
My original telephone extension cable is the basic 4 core telephone type (also from Maplin) and simply does not work (there no broadband lock). In addition, the BT roadside box is also about 2.5 miles from the exchange, which is why there is a max 512K speed limitation on my line.
In short, in my sort of dodgy location the extension cable type/quality matters a great deal!

  mike1967 23:34 08 May 05

I'm using CAT 5 with about 20 metres in length to network 2 PCs together and no problem at all, also using a 10 metre extension lead to get the broadband to the first PC, so I don't think the distances are the problem as I running at 2 meg.

  JOHNKM 17:58 09 May 05

I have just discovered that the loss of ADSL lock is nothing to do with my 20m length of CAT 5 cable.

Over the past two days, I have occasionally noted periods of a few hours where ADSL lock
did not fail when using the phone, but the final confirmation came when I
had a friends computer in for repair and after completing the repair, I set
it up beside the BT socket and installed the modem. I immediately found
ADSL lock was lost in exactly the same way as I have experienced on my main
computer at the end of the CAT 5 cable (I checked this happens with both
filters). It seems that when we checked this on my daughter's laptop afew weeks ago (just
before she went back to university) it must have been during a 'good'
periods, which has clearly confused the issue.
Therefore the fault must either be in the modem, or BT's line quality is very marginal, due to losses over the 2.5 miles to the exchange.
So much for deciding to have the slower 256K broadband so that there would be no problems!!

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