Any Telephone Engineers on the forum ?

[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

[awemawson]

Out of interest I put my (ex BT) Tektronix Time Domain Reflectometer on my internal wiring this morning. Proved total cable length from Master Socket to internal Panasonic Exchange is 67 metres, with minor reflections from each of the Krone junctions on the way - largest being the first which is 26 metres, the next one being a further 10 metres down line. I did try re-making the punch down connections on the first Krone but it made no detectable difference.

I always find it fascinating that reflections from an 'open line' have the same polarity as the out going pulse, so hump upwards on the graph, whereas if you loop the line by putting a link across the far end, the reflected pulse goes negative (downwards)

This particular instrument allows you to calibrate it for cable characteristics by using a known length of the type of cable that you are measuring, so I cut an accurate 10 metre length of  the same cable, and set it up so it measured correctly by setting the propagation velocity for the cable in use.

https://en.wikipedia.org/wiki/Time-domain_reflectometer#/media/File:Partial_transmittance.gif

I also did a 'loop resistance' measurement giving 12.2 ohms for the 67 x 2 metres of wire, which works out at 91 ohms per kilometre. As it's apparently nominally 84 ohms per kilometre there's nothing too horrendous I think.

[trevoratxtal]

I am sorry I am unable to help on this matter.
But would like to thank all input from folk as it has been most informative.
Very useful posts. 

[awemawson]

Well interesting results today 

Before Mr BT arrived, by chance I was running a logging program, reading noise margin figures from the Home Hub 5a, and charting them. Then the 'phone rang, one of those nuisance calls that this time did me a favour 

The noise margins went all over the place and the Hub disconnected and restarted! When it was back up, I called my number from my mobile, and sure enough I could reproduce the effect 

So bright and early, Mr BT came, put his magic gizmo on the line, pressed a few buttons and diagnosed "Rectified Loop Fault' - most likely a damp connector block somewhere. Well the outside line comes from a pole in the road, to our gutter board, down the wall and appears on the other side of the lounge where the Master Socket is - but the Master socket has internal type wire, whereas the outside line disappears into the wall in external type cable. So there must be a joint box under the floor. 'There's your fault' he says. Hang on says I - prove it to me, ladder up to the gutter board, cut the cable and test again BOTH ways - into the house and back to the Exchange. He does this and guess where the fault is? Yes - on the line to the Exchange (Phew !!!!)

So off he trots to the Street Cabinet (which is over a mile away) does a few things, runs his tests again - ALL CLEAR. So what did he do? Used a different pair from the Street Cabinet to the Exchange, and used a different pair from our gutter board to the Cabinet (luckily it's as two pair)

The ONLY bit of cable unchanged it that under our lounge floor AS IT's OK 

Hub up and running, seems immune to incoming calls and connected at 22 Mbps 


Early days of course - only been up an hour or so 


Graph attached: 1st disturbance was the nuisance call, 2nd disturbance was me calling on my mobile.

[John Swift]

that's a good result
nothing to pay and it now works !!!

   John

[Will_D]

Great result there Andrew. Always pays to be persistent and get them to do the job thoroughly!

[philf]

A few years ago we had a problem with our phone. The line could be so noisy that some times you couldn't hold a conversation.

We called out BT 4 times with the threat that if the problem was inside the property we would have to pay. Like Andrew I had disconnected all my internal phone wiring to rule that out.

Because the problem was intermittent you could almost guarantee that, on the day of the visit, the line would be OK.

The first engineer remade the connections in the connector box on our wall, checked the line (which sounded OK) and left. Within an hour or so it was as bad as ever. The 2nd and 3rd engineers stuck a meter on the line and declared everything OK. (As it may have have been when they left.)

I was now getting p***ed off and recorded the phone when it was particularly bad.

The 4th engineer came and he only looked about 20. After explaining the problem, playing the recording to him and telling him he was the 4th engineer to try to fix it his first question was - "Is your broadband OK?" - which it was and always had been. "Ah - then the problem is between the cabinet (100 yards from our house) and the exchange." He disappeared for 15 minutes and then came back saying the connector disintegrated when he touched it so he remade the connection.

It seems logical now that if the fibre broadband is OK then that immediately rules out problems internally and externally as far as the cabinet.

It's been absolutely fine since.

Obviously some of the OpenReach engineers are brighter than others.

A mate of mine got so fed up being told there was nothing wrong with his line he shinned up the telegraph pole outside his house and replaced the cable to his house!

Phil.

[DMIOM]

...... Then the 'phone rang, one of those nuisance calls that this time did me a favour .... The noise margins went all over the place and the Hub disconnected and restarted! When it was back up, I called my number from my mobile, and sure enough I could reproduce the effect .....

Glad you're sorted Andrew - another good lesson in diagnostics.

A few years ago, I had a slightly similar beneficial effect from incoming calls, but for different reasons. Audio on outgoing calls was very low, but incoming calls were fine; then I noticed if I rang out immediately after an incoming call, audio levels were OK. Experiments showed it wasn't the actual call that had the beneficial effect, it was the ringing - it looked like a few cycles of bell voltage were sufficient to blow away the damp or the spiders or whatever was affecting the overhead string, so for a while immediately prior to making an outgoing landline call I had to dial my own number using my mobile and let it ring a few times. Much testing & remaking of joins in the overhead network and eventually all was OK.

Dave

[tom osselton]

Years ago my livingroom phone rang by itself  you could answer ok but would ring as soon as it was put down. The repairman disconected all the phones in the house, reconected the one in the kitchen and told me if I wanted the others hooked up it would be at $50.00 a hour! I just went to the cell phone!

[awemawson]

Well the system has been 'up' and running absolutely solidly at 21.45 Mbps with no hiccups ever since Mr BT left 


OK not quite true - I took it down myself today to re-arrange my internal LAN network. I give the guests in our holiday cottages free access by WiFi to the interweb but I don't want them to have access to the numerous PC's and other devices on my network, so the WiFi Access Point that they use is hidden on a branch of the network behind a "VLAN Switch"

This is a clever device with 8 Cat5 ports. You can control which port 'sees' which other ports. So my LAN from the Home Hub 5a enters on port #1, the WiFi gizmo is on port #2. Port #2 is programmed so that it can only 'see' port #1, whereas all the other ports can see everything EXCEPT port #2.

As the Home Hub had been moved from my office. back into the house 67 metres away this involved patching from the Home Hub through my jungle of patch panels down to the office to connect to the VLAN Switch, then one port on the VLAN Switch comes all the way back again to the house, where another simple 8 port switch distributes to various rooms and bedrooms.

Fortunately, when I first installed the ducts and patch panels I pulled 6 Cat5e cables through as well as several 'voice' telephones, so there was enough redundancy in the system to give me sufficient cables.

... planning ahead you see 

[Will_D]

Jeez, How much time do you spend in the outside loo to need a dedicated service??

 

We want to see your Bog!

[awemawson]

I wondered if anyone would pick that up and run with it 

When I was trenching new soil runs in from the house to our private sewage system, I decided to resurrect the old outside loo as the trench went right past it. As I was also putting in water  pipes and trunking for mains cables to it, I decided to go the whole hog and run telephone extension line and a CAT5e leg from the nearest patch panel.

The idea was to put a WiFi access point in the loo to cover the garden, but in practise I never have. However having a telephone extension there is very handy if the phone rings and we're in the garden 

[Will_D]

Andrew, I commend your forward thinking:

"If youy are going to a job do it properly!"

[awemawson]

Here you are Will, just to satisfy your toilet picture fetish 


You can even see it from space - see the last picture 

[modeng200023]

Andrew, hope the illegals don't see this. They will settle in nicely

[tom osselton]

It seems far enough from the house for those bad days but where is the flatscreen and beer cooler for the games?

[tom osselton]

For the illegals that part is easy just install speakers under the throne they will think it is haunted! 

[DMIOM]

Adds a new interpretation to "just going to pay a call" - and have you wired any of those buttons on the telephone set up as button "A" and "B" for those spending a penny? - and with all that electrickery on tap, is the door solenoid/RFID locked?

Dave

[awemawson]

Shortly after we moved here, we had a visit from a fellow (Neil Farrow) who leased the farm from the 1950's and subsequently bought it when the 'leasehold reform act' came into being. He was in his nineties, and so much had changed since he was last here, literally the ONLY thing he could recognise was the Outside Loo - I didn't dare show him what was inside!

Apparently he was the first person in the village to have a tractor - popped his clogs now poor chap.

[daber]

This is a bit off topic  but I had a problem with DSL and my Actiontec M1000 with drop outs and reboots.  Century Link said it was my modem so I changed modems after considerable back and forth testings and conversations with tech support.  That temporarily solved my problem.  I being an electronic tech sort of guy opened up the original modem and found bulging caps so I replaced them and it has worked perfectly ever since only have a few dropouts over 6 months.  I also opened up the second replacement modem that was as used unit also and found the same bulging caps and a few more.  I replaced those too and retested with the same good results.

[Pete W.]

Hi there, all,

This has been a very interesting thread - thank you all.