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Any Telephone Engineers on the forum ?

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awemawson:
How do you test the INTERNAL cabling of a 'phone installation ?

Back ground - just upgraded to BT Infinity which has more than doubled our download speed, but the router (BT Home Hub 5) is dropping out several times a day. BT Helpdesk are trying to tell me it's my internal wiring, but it isn't as it still drops out when the internal wiring is disconnected at the Master Socket - Engineer coming Tuesday with dire threats of large bills if my (no longer connected !) internal wiring is the cause.

OK I'm pretty sure of my ground, but it raises the question, How do you test twisted pair telephone wiring? Is there some sort of frequency response graph you can generate?

My system is very simple, as the (filtered) incoming line is only connected to one device (a Panasonic DBS Telephone Exchange), however there are several joints properly made in Krone Blocks along the way as it's 50 odd meters from the Master Socket and the cable goes through three underground ducts and two buildings.

I have an (ex BT!) Time Domain Reflectometer, so I may try and see if the joints show up as reflections in the trace - but apart from that how do you test this simple twisted pair ?????

John Swift:

Hi Andrew

I'm not a phone engineer but I agree with you its a BT problem
 if it still drops out with the Panasonic exchange and any other device disconnected from the master BT socket


for each telephone connected to the exchange
I assume the ringer wire is not used and the incoming A & B pair of wires are connected  via the exchange to a  LJU2/2A   PABX Master IDC Socket

( the  LJU2/2A looks like a LJU1/1A Master IDC Socket, with just a capacitor, the  resistor and surge arrestor having been removed )

as I under stand , the new NTE5 Master Line Box with a ADSL filtered faceplate fitted
has a RJ11 socket to connect the hub directly to the incoming line
and a filtered socket to plug in your 431A telephone plug -

 the filter  presents a high  impedance  to the ADSL signal on the phone lines A & B  to stop the telephones short circuiting the ADSL signal
 
 on the latest face plates a choke has been added to the ringer wire to isolate it from the incoming line  , this helps to maintain the maximum broad band speed

if the extension sockets are connected with 2 or 3 pair cables
you only need to find one working pair to use a  LJU2/2A socket
 a use full fix if the cable has been damaged


   John
 





 
 

PK:
The clue is the "double the download speed" bit.
SNR on a twisted pair is a function of sync speed. When SNR drops to a certain level (4-5dB for most consumer systems) then your modems (or the modem inside your devices) cant lock onto the carrier waveform(s) and you lose sync.
Forget the 50m of wire in your house. So long as you don't have anything else plugged into it (and you haven't coiled it up under your inductive cooktop) then it's going to be fine..
The key to understanding what's going on is getting to the diagnostic screen of your modem/device. It will tell you what your SNR and distance to the exchange is. I've attached a pic of mine:

If you know where your exchange is physically located, you can do a quick check by plugging the measured attenuation numbers into something like this: http://www.speedguide.net/dsl_speed_calc.php

The ultimate fix is (sadly) always to ask BT to apply a stability profile to your connection. This is where they reduce the sync speed (and your download speed) in steps until you get to an acceptable level of stability.

awemawson:
Googling about a bit I've managed to access the internal fault log and every disconnect is triggered by an:

"Event code 4 value change"

Now googling that it seems to be a known fault of the Home Hub 5a and BT have known about it for well over a year. There is supposed to be a firmware fix, but in actuality it seems to be more of a configuration tweak on the BT side of the set up.

... Well we'll see on Tuesday when the man comes !

PekkaNF:
Telecom comppanies does not seem to be pleased to make house calls, some years back I had to fight to get anybody to visit here....I had some problems with internet provider too...I was payning to get 24 meg (max. "sigh" speed) and it was always less than 10megs, which they said would be still within "service promise". I called them several times and they said they record the conversation and if the fault is inside the building, just finding it out would cost 70€ etc...after stalling for a month, they sent someone who didn't bother even to come inside and made some some "tweaks", which slowed down the speed a little and added latency - great. 3g gave better speed but speed varied a lot.

Only when I got optic fibre, the speed got better and stable.

Pekka

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