Kitz Forum
Broadband Related => ADSL Issues => Topic started by: Loading on January 24, 2014, 01:57:05 PM
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What should the voltage on line be i know 50v dc, but it 49.3v close enough?
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It can vary a hell of a lot more than that! :lol:
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It can vary a hell of a lot more than that! :lol:
Yeah I know that, but there is also an intermittent crackle, and constant hiss only when router is connected?
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Nominal voltages for a bog-standard line are 48v on System X Exchanges, and 54v on System Y Exchanges. But as HP points out, certainly don't 'work' to those exact figures if faulting a circuit. There or thereabouts, is a good rule of thumb. :-)
It sounds like you have a potential HR (High Resistance) fault. Trawl the forum using the 'Search' function to learn more about this.
Just for info for others curiosity, there are other types of circuit that have different nominal voltages. DACS = 140v and ISDN = 90v. :)
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Nominal voltages for a bog-standard line are 48v on System X Exchanges, and 54v on System Y Exchanges.
Interesting. :) I did not realise that the two System exchanges had different nominal working voltages. Under normal (non-fault) situations I have only ever observed 52 >= Vpair >= 48 . . . probably because I have never "played" with a pair connected to a System Y exchange.
That got me thinking . . .
System X -- manufactured by GEC, Plessey and STC and now maintained by Telent.
System Y -- manufactured by Ericsson.
. . . am I remembering correctly? :-\
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Hi B*Cat ……. as always you are 100% correct with your observations. My one caveat, is that I wasn't aware that Telent maintained the Sys X Exchanges, but then again I wouldn't know as part of my day job. Forever learning. :graduate:
The only other factoid I can maybe enlighten you with, was that Sys X were installed in far larger numbers than the Sys Y ever was. Certainly around the North West area, anyway. Also, I believe that the defunct Exchanges (Crossbar/Strowger/TXE2/TXE4A) that these new digital Exchanges replaced, were decommissioned, stripped out and rebuilt in other countries, namely Africa ?
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For some reason Marconi also rings a bell with me.. My memory is hazy, because I visited a large sys Y exchange and my local sys X which Im sure someone mentioned marconi.
Im now getting things muddled because it was so long ago, but if BS can confirm that this photo below is the sys Y equip, then Marconi was mentioned for sys X (ie the others).
Around here afaik is was the smaller exchanges with sys x.. and only the 'posher' exchanges with sys Y.
Apologies if I have that the wrong way round hence asking for clarification via the photo identification.
(https://forum.kitz.co.uk/proxy.php?request=http%3A%2F%2Fwww.kitz.co.uk%2Fadsl%2Fimages%2Fphotos%2Ftelephone_linecards_1.jpg&hash=c1868401585560ff05e0e792297efd8bd5a0bc5c)
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Alas Kitz, I couldn't tell you if I wanted to, what vendor of line cards those are ?? The Exchange Construction TO's were responsible for the installation and commissioning of said beasts, back when they were being installed. Some of the other ex-BT posters on this forum will tell you, there was quite a hierarchal system at work back then. Mere T2B's and T2A's (as they were then) were hardly spoken to by the far superior TO's. So, requesting a peek at what they were doing was out of the question. :-X :)
I hasten to add, they weren't all like that. The majority probably were though ?? They tended to end up as local Magistrates.
Also, to fly in the face of your experiences, the smallest Exchange on our patch went Sys Y, whilst the rest went Sys X. Again ….. who, how, where or why the allocation ended up as it was, is not something I'll ever be privy to I'm afraid. It's approx 26/27yrs ago since they were introduced.
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Thanks anyway BS. :)
All I can recall now is that the housing/frames/cabinets (or whatever the correct term is) were different. It was the BT Wholesale guy who was doing all the talking when it came to be that that particular photo was taken.
Both the frames and the field engineer who'd been allocated to me that day also asked if they could accompany me when it came to time with the BTw guy, as they also got to see and hear things that they wouldnt normally do in their everyday work. TBH I was trying to get as much info as I could on 21CN and backhaul info from him so didnt really concentrate on the telephony stuff. :(
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I know that GEC eventually became GEC-Marconi . . . before both names ultimately became defunct!
I have heard that System X exchanges are sometimes referred to as Marconi exchanges. Which would tie in with the above. :)
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What should the off hook voltage be? Mine being 9.5v fine?
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What should the off hook voltage be? Mine being 9.5v fine?
Yes, I'd say that is "purrfect".
As an example, I have just checked my own pair --
Pair Status BE AE BA
Not looped 50.9 1.2 49.7
Looped 36.6 29.3 6.7
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...and a regulated current of around 40mA.
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Correct 4Candles. :)
Open circuit line-voltage and line-current feeding:
Network batteries have limits in the range 40V to 57V. The positive pole is earthed. Ripple components up to 2mV psophometric may be present. Adaptive line-feed circuits may connect up to 70V to the line. Depending on line resistance, currents as low as 25mA may occur. The idle condition is a battery condition on the B wire and an earth condition on the A wire. Both conditions being supplied by the network.
Modern designs of telephone exchanges will give an essentially constant current line feed with a nominal value of 40mA. However, when the total loop resistance is high, the feeding circuit becomes essentially constant voltage.
The maximum current (µA) that can be drawn from the network by any customer apparatus that is in an off-line and idle state and is connected to a standard exchange line service must not exceed a figure that is equal to 30 times the REN (Ringing Equivalence Number). The maximum number for the REN is 4, therefore the maximum line-feed current that can be drawn from the network for a single standard exchange line service in this condition is:- 30 x 4 µA = 120µA
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Thanks for the confirmation Mr Sheep, and the further interesting info. :)
I remember being surprised some while back that there was virtually no difference in the current measured whether the DMM was in series with a phone or straight across the line with no phone...
...and then finding that it was still 40mA when I moved to a property with a much shorter line.
All a bit different to my analogue switching days, when IIRC line currents were more in the order of 80 - 100mA.
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A pleasure, 4candles. :)
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Mention of a constant current feed prompted me to experiment. ;)
Connecting my ex-Beattie Fluke 8022B across the pair and measuring the voltage showed 49.7 V. Switching to measuring the current showed 27.9 mA.
Hmm . . . I wonder if that is meaningful? :-\
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Mention of a constant current feed prompted me to experiment. ;)
I just knew that b*cat would be curious. ;)
Initial thoughts suggest either an extremely long line, or some kind of low insulation or earth contact fault.
I have to go and see a man about a socket this morning, but the decade boxes beckon on return. :)
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How would I test the current? I tested it with phone on hook it one room, and on another socket in another room, and if got 0.02mA, how would I test properly?
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How would I test the current? I tested it with phone on hook it one room, and on another socket in another room, and if got 0.02mA, how would I test properly?
Un-plug all the phones, etc and connect your DMM (set to the appropriate mA range) directly across the pair -- as if you were measuring the on-hook voltage.
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Mention of a constant current feed prompted me to experiment. ;)
I just knew that b*cat would be curious. ;)
All kittehs are curious! ::)
Initial thoughts suggest either an extremely long line, or some kind of low insulation or earth contact fault.
Line length -- DS / US Attn(dB): 46.0 / 27.3. According to Kitz (http://kitz.co.uk/adsl/adslchecker.php), direct: 1.8 km & by road: 2.4 km.
Low insulation fault -- may be.
Earth contact fault -- unlikely. (I'd probably have noticed. ;) )
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All kittehs are curious! ::)
Naturellement. :)
Your conclusions seem entirely reasonable b*cat.
Experiments continue at Chez 4C:
Taking into account Exch - cab - home distances, and the likely time of infrastructure installation, I'd guess my loop resistance to be roughly somewhere around 200 ohms.
With DMM and decade box in series, and together across the line, the current was measured as 39·75mA, and didn't start to fall off until the decade box was on 830 ohms.
A high impedance monitor was also across the line, which revealed that dial tone could still be obtained up to a box reading of 4130 ohms, with the current at 11mA.
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How would I test the current? I tested it with phone on hook it one room, and on another socket in another room, and if got 0.02mA, how would I test properly?
Un-plug all the phones, etc and connect your DMM (set to the appropriate mA range) directly across the pair -- as if you were measuring the on-hook voltage.
I did this, and still only got 0.02ma, I also tested one of the wires the the positive lead on the mm, and the negative to earth, and got 53.4v, where I connect both the phone wires, I get 49.3v, if i connect the other cable to the mm and to earth i get -3.1v? so why is there 3v lost?
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Is it not because of the 'Volt drop' when testing between the pairs, i.e.: the resistance of both wires combined from the Exchange ?? In effect you are testing through both legs of the circuit, whereby your other tests are from each individual leg to your own 'local' earth.
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Why are my current numbers so low as I only got 0.02mA in the test socket, with nothing else connected?
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I don't know about that, bud ?? It's obviously not right so were the leads connected properly ?? Not doubting your ability for a minute, just wondering if there was some 'High resistance' between the meters leads and the adaptor you are using to test at the master socket ?? :)
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Aha, I'm left wondering if you've gone directly across the pair, as you would testing for voltage ?? To test for current you would need to put the leads from the MM 'in series' with the 'feed' wire. I'm just guessing that's what you've done as I have no idea what adaptor you are plugging your MM into ?? :)
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Un-plug all the phones, etc and connect your DMM (set to the appropriate mA range) directly across the pair -- as if you were measuring the on-hook voltage
Yeah I went directly across the pair, how would I plug in series with the feed wire? It was an old cable with a phone jack at one end.c
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The Internet dropped today, I am kind of starring to think that constant rain affects it, with the upstream resyncing lower, at 320kbps, with a lower snr, checked voltage on pair, was 49.0v, then lifted phone and replaced, checked again and was back to 49.3v? What would be causing this?
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. . . checked voltage on pair, was 49.0v, then lifted phone and replaced, checked again and was back to 49.3v?
Granted you can measure such a difference but is it relevant?
100 x ( 49.3 - 49.0 ) / 49.0 = 0.6 % change in observed voltage.
What would be causing this?
:shrug2: Space-aliens? The elderly widow, down the road, had just finished a telephone call to her younger sister in Harrogate?
Seriously, I do not think that observed difference is meaningful or relevant.
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Just as note never stick the A & B wires onto ones tongue to test if there is a voltage thats so 1970's you will get a nasty shock if you do, if it arcs blue from + to - terminal please use a multimeter ;)
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I have no idea what the YouTube video is showing, the conditions under which it was recorded, etc. So just ignore it.
What exactly are you trying to discover (or prove) about your circuit? As far as I can determine, it is operating within specifications.
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The timing of the display changes strongly suggest that there is ringing on the line, which I believe is nominally 75V RMS.
It looks to me, though, that the meter is set to a DC voltage range. :o