Oh, its even worse than that. The ringers I recall from the days of mechanical bells all had inductors that had a little flapper (just like on a relay) that normally had an air-gap. When the flapper was pulled over that gap closed. That changed the inductance greatly. The resulting dL/dt puts a nice spike into the otherwise smooth 20hz sine wave.
The full equation for the voltage across the inductor is really
e = L di/dt + i dL/dt
We are so used to working with fixed-inductance inductors that it is easy to forget about the (i * dL/dt) term.
To see this dL/dt effect in action one can drive a relay with a low-frequency sine wave (say 1hz - 10hz) and put a scope probe across the relay. At the point the relay pulls in one should see a little spike. It might help to increase the signal generator's impedance a bit by adding a series resistor.
I think he's talking about drop wire. I know GTE used to use non-twisted pair drop wire in a lot of places. I always thought it was a damned fool idea, but...
....
Used to drive GTE right up the walls...
Back in the early 80's I worked on Eielson AFB, south of Fairbanks, and most of the time they had a humongus 1800 Hz tone induced into every pair on the base. We did eventually determine the exact source, but were not able to get it fixed. The base power plant had one particular generator that produced it. If that generator was on line, it was everywhere.
Now who is being pedantic? Voice is nowhere near data in frequency. So the truism of idential impairments has no practical effect.
??? most of telco outside wire is Cat0, essentially identical to silver satin but solid with weather/burial protection. A lot of older wire is even worse, with even paper insulation. Yet hundreds of millions of circuits all work fine over thousands of feet per run.
Of course twisted pair is better. Expecially an EMI noisy environment. But the difference is marginal. With digital, marginal effects can make large differences.
Precisely. Which is why local field strength is an issue. A split pair causes no trouble if there's nothing to interfere with it (troublesome freq). One split voice pair in a shared sheath isn't much problem, although it will pick up more 60 Hz hum. Two are definitely a problem, especially since they're likely to be split on each other. Either way, the data won't care so long as it's not split.
Granted, but I see that difference small (~20%) comparing with with twisted pair. And under some circumstances, non-twisted pairs would be _worse_ than split pairs (think side-by-side flat pairs vs USOC)
More than that. I've pushed 10baseT fine through 50ft silver satin with USOC pairing. It totally fails as side-by-side. I suspect 10baseT could be pushed through a good length of quad with diagonal pairing so long as it wasn't too kinked.
A 45.5 baud 130 mA circuit maybe, Floyd? With an KSR 28 on the end....
Huh?
I agree with Floyd here. Only butt-ugly 2 conductor drop is untwisted. And I don't know that Ma even uses it anymore..
[pulp]
If you think pulp cable is not twisted, you've got some manhole [OOPS "maintenance hatchway"] time coming. All that lead-sheathed cable is quite twisted. [A local crew just cut 600' of ~1200 pair pulp out and replaced it with icky-pic. I stopped and chatted several times. The MH was so cramped they were doing only 100 pairs a day....]
.....
Take a battery-power scope and go find a field far enough away from the grid that you can not see 60Hz on a 10' long antenna...
Pedantic is not usually considered desireable. This discussion started with a very simple question to which I and others said "It's OK so long as you don't split a pair".
Please see the Subject: line for a precise definition of the data & voice we are discussing. I maintain my point that these vastly differing frequencies (aided by balanced signalling) greatly reduces the _effect_ of interference.
Newer cable most certainly has some twist. Older cable was more rolled as a bundle(s) than twisted pairs. The roll helps against external fields (60 cycle hum) but doesn't help crosstalk.
Certainly vastly at 10baseT (and moreso at 100baseTX), but the difference is much less at ADSL freq.
Yes, quite true. The downside of digital is less discussed. When the error rate significantly exceeds the design BER, then the whole thing fails entirely. Think of a BER of 0.1% on TCP/IP. A split pair on 10baseT often causes less.
We are talking a single POTS circuit and 10baseT two pairs inside a single sheath. See the OP.
External fields are not the only cause of induced noise. Crosstalk is very severe in a split pair cable, and governs many 10/100 systems. It's what causes longer lengths of Cat3 to fail in
100baseTX.
Longitudinal imbalance? A split pair is nowhere near as bad as putting raw signal (no baluns) across coax as you cited. The impedence of the shield is hardly specified, and even the signal pathlength and velocity of propagation (slew) will be different. Yet you reported it worked over 150'.
The impedence of a split pair will be off quite a bit, but at least both splits will be the same if they're against similar (grounded/floating) conductors.
Of course I know what split pairs are. I like to say: "Electrons may be color blind, but they know who their dance (twist) partners are." And obviously splitting pairs involves more than one pair.
Consider the classic newbie goof -- RJ45 with pairs in sequence. pins1&2 are paired and 10baseT in one direction runs fine. Pins3&6 are split so the other direction is full of errors (may not fail at 10, but most likely will at 100). But if POTS has been put where it usually is (4&5), this pair is also split, but against the ethernet split! I'd have to double check the Left Hand Rule, but I believe this doesn't cancel but amplifies crosstalk.
Folly? It's been working fine for a year, even with considerable flex. It can now be easily fixed, but there's just no real driver until it fails.
Of course it's a failure risk. But people have a right to take informed risks. Standards are good and should be followed, but sometimes the cost of complaince is greater than the risk-adjusted cost of failure.
Actually, they were likely 60 mA or 20 mA. Incidentally, I started my career overhauling teletypes. I worked on M32, M33, M28 & M35, among others and my first computer printer was a M35 ASR, which I bought surplus from my employer.
When you have people arguing technical details they don't understand, pedantic attention to *correct detail* is extremely important. Hence, while it may be true that pedantic is not usually considered desirable, in this thread it has been essential.
The subject line does *not* provide a definition for either data or voice. 10baseT and POTS are specific, not general, forms of each. If you want to say 10baseT and POTS, say it. Regardless,
*you* have discussed several other forms of data in this thread. (Such word games are exactly why it is necessary to be pedantic.)
Regardless, you are still wrong. The impairments are the same, all that differs is the intensity; and understanding the mechanism, which is the "truism", is important.
It does. And in a properly installed and functioning example the interference will be below the critical point, and the circuits will be deemed to be functional. However, saying, for example, that 20 Hz ringing on a different pair will not be a problem in such a circuit is vastly different than saying 20 Hz, because it is on a different frequency, can't ever interfere with 10baseT.
Total nonsense.
The cable pairs are twisted. In fact each pair in a bundle has a _different_ twist, to prevent any two of them from getting too cozy. Then the whole bundle of twisted pairs is swirled. And then all of the bundles are swirled within the sheath itself. That is the way multi-pair cables have been manufactured for many many decades.
Most power influence *is* crosstalk, between a comm cable and a power cable. Anything that helps one will help with 60 Hz will also help at VF and above, and as we've both noted previously the effects are greater at higher frequencies. Which means it is exceedingly difficult to do something which helps at 60 Hz and does not have an even greater effect at VF or above.
Regardless, even at VF twisted pair is *vastly* better than flat satin non-twisted cable. It is not a "marginal" difference.
Nonsense. I don't even know where to start correcting that, because none of it makes sense.
When the error rate significantly exceeds the design BER, what happens is... the error rate exceeds the design BER. That doesn't cause a catastrophic failure. Typically a progressively higher BER will cause some degradation of the data throughput for certain types of protocols, TCP being one. IP may or may not be much affected... which is to say the effects on UDP will be different than the effects on TCP. That is because UDP is not a "reliable" protocol (and thus will be greatly affected) and TCP is (and will merely be slowed down).
A BER of 0.1% strikes me as exceedingly high, given that the target on DS1 facilities is 1 x 10e5, and you are talking 100 times that. Given that most DS1 facilities run more like 10e8, or another thousand times less, I'd say that a split pair causing a 1x10e3 BER is in *extremely* bad repair.
What I said is still true and what you said was not.
If you split a pair using CAT3 or CAT5 for 10baseT or 100baseTX, there *is* going to be a problem. A short length measured in feet will work with 10baseT, but for 100baseTX it will be measured in inches. Both are necessarily the multi-pair example I described above, with or without a POTS circuit present.
Crosstalk *is* an external field.
It is *exactly* the same thing at the end of the cable where a differential detector is expected to make use of common mode rejection.
So?
Exactly. And that will lead to both phase and amplitude distortion which differs between the two wires of the pair, and that results in amplitude distortion for the facility as a whole.
For an ADSL loop. Do you understand that no doubt means that a similar length of CAT3 with a split pair stretched out in the same place would work equally well?
So? It might be, but it might not be.
Then why were you babbling about having only one pair involved?
More nonsense.
Wired that way there are two split pairs, period. Whether POTS is put on the second split pair or not will make little difference to the 10baseT using a split pair. Putting POTS on
*any* pair, split or otherwise, in that cable is going to be a problem for the 10baseT signal on the split pair. Which is to say, if the pair is split, *any external field* will induce a current and cause problems.
I have no idea what nonsense you are referencing in regard to a Left Hand Rule and crosstalk cancellation vs. amplification. And I hate to think what it is you mean...
It is pure folly. Abject foolishness. (Am I clear enough?? :-)
My bet is that you have no idea whether is works well or not! I saw a guy "splice" some CAT5 once. It was a 175' or so run and at about 125 feet the roll ran out. So he got another roll and literally tied the two cables physically together with a knot and then split out each pair and twisted the wires together and taped them up, and finished the run.
It "worked"! I told him, as did a couple other people, that is was too ugly to live and that he ought to be shot. Not to mention that I didn't believe that it worked anyway.
You know, it "worked" just fine. The PC it went to could access the LAN. What can one say, eh? There was this nagging problem that that PC for the next 6 months would hang, sometimes several times a day. And when IT tried to work on it remotely they usually could, and nothing would be wrong, and sometimes couldn't get into it at all.
We finally got fed up and found someone with the authority and the understanding of cable, showed him that splice and he "authorized" the culprit to run another cable for that PC.
On an Ethernet, particularly using IP, it is relatively difficult to know just how bad some of these things actually are...
Exactly. David Lesher and I both had comments previously about doing exactly that. But given the strange ideas you have about how all of this works, I can't see what you are doing as an "informed" risk.
Sounds strange that telephone ringing voltage would cause this when you plug RJ11 phone line to the Ethernet card. The reason for that is that Ethernet signals are isolated from computer circuitry with isolation transformers that pass pretty much only high frequency signals shtough them and provide 1500V isolation between computer side and line side. Other thing is that the telephone line signals and Ethernet signals typically are wired to different pins on the RJ-45 connector. In typical 10Base-T Ethernet cards those pins used for telephone signals are not connected to anything, on some cards there not even contacts on those places in RJ-45 connectors... The 100 Mbit/s Ethernet cards typically have some resistors connected to wires not used by Ethernet.. Feeding telephone signal to those could lead to smoke coming out of those small SMD resistors but I would not expect much else... With a properly designed Ethernet card it is hard to believe your story of the damages.
If that RJ-45 connector was carrying something else than Ethernet, I could better believe the damages....
Multipair telephone cable is twisted pair, nowhere near the level of twist you'd find with data cable though. The only non twisted pair you are likely to find on the telco side is old single circuit drop wires.
There isn't anything wrong with paper as an insulator.
Though typically you have to use compressed air to keep water out if the outer jacket springs a leak.
2&3 of the RJ11 this would correspond to pins 4&5 of the RJ45. On many NICs pins 4,5,7 & 8 are not connected to anything (in some cases the connectors arn't even present in the socket). Even if you have the line on pins 1$4 of the RJ11 the RJ45 connects directly to an isolator, even with a NIC built onto the board.
Not even that is a good guide. Since an installation may have been made long after the building was constructed. Especially with overhead drop wires. If it looks like an old piece of cable is causing problems it's going to get replaced by more modern cable.
Both ISDN and ADSL are specifically designed to run over existing cabling. It would be incredibly expensive to have to replace all the underground multicore.
The basic problem with ringers is you can not pump enough power down that long resistive loop to just make a mechanical ringer work as (say) fire bell does. [Now, we have tweedle-deedles that take nil energy, but......]
So the original telephone wisemen came up with our low freq scheme. I thought it worked because even the straight-line ringers were mechanically resonant, but someone else points out they can't be or they'd not respond to non-20 Hz.
Somewhere, years ago, I read a detailed explanation of the ringing scheme, which covered not just how but why. Can anyone point to a write that goes into depth over this issue?
The basic problem with ringers is you can not pump enough power down that long resistive loop to just make a mechanical ringer work as (say) fire bell does. [Now, we have tweedle-deedles that take nil energy, but......]
So the original telephone wisemen came up with our low freq scheme. I thought it worked because even the straight-line ringers were mechanically resonant, but someone else points out they can't be or they'd not respond to non-20 Hz.
Somewhere, years ago, I read a detailed explanation of the ringing scheme, which covered not just how but why. Can anyone point to a writeup that goes into depth over this issue?
There are regions that can cover several countries that are run in sync. So with those it is quite easy to buy and sell electric power across the borders.
And there are solutions for bying and seling electric power across unsynchronized borders. The most common solution is DC power links. The power is converted at one end to high voltage DC, transfered as DC through long distance (for example across tens or hundreds of kilometers of sea) and then converted back to AC syncronous to the network at receiving end. And those links are designed in such way that they can be run in both directions as needed.
There are also frequency conversion units that can convert electricity between different networks...
Ectricity is sold and bough actively between many Northern European countries through Nordpool
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Nordpool is the Nordic electricity exchange for physical electricity trade. There is a quite real time display (updates every 3 minutes) how much electricity goes in and out of Finland at
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you browse around you can also
The European Union aims to create a European internal electricity market.
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