ADSL works over wet string (2017) • Hacker News Board

Re: ADSL works over wet string (2017)

#141

Post by djweis » Sun, Dec 05, 2021, 2:59 PM UTC

jcims wrote: post #30

tenebrisalietum wrote: post #18

Earlier quoted context omitted.

I think this is common in places where they don't expect moisture to reach, but then things change and it gets there anyway. If your POTS lines are down and the telecom company is telling you a "wet pulp repair" is underway, your phones are going to be down for a while because a bunch of paper-insulated cables need to be manually rewired because they got wet and corroded. I found this interesting: http://etler.com/do…

I know there are some telecom folks on here that may be provoked to correct me but pulp was standard before the advent of cheap plastic insulation in the 1950s on up. I live in the midwest and my brother is a lineman for AT&T. There is an astonishing amount of pulp-insulated phone line still in service today. In order to keep it dry, the conduit that the pulp lines are run through is pressurized to 5-10psi. Anyone th…

There is still a lot of it in service. Sometimes you'll see a tank of nitrogen chained to a pole. It is there to put pressure through the cable to keep water out of a cut/nick on the lead sheath. The lines are pressurized normally from the central office and if the monitoring shows a drop in pressure (a cut in the sheath), they roll out cable maintenance.

Re: ADSL works over wet string (2017)

#142

Post by neilalexander » Sun, Dec 05, 2021, 8:07 PM UTC

cpgxiii wrote: post #118

toast0 wrote: post #78

Earlier quoted context omitted.

Sadly, there's not much in the way of equipment for this. I could really use two small 10BaseT-1 to 10BaseT converters, preferably both powered from one end.

Since most of the 1000Base-T1 gear is still unreasonably expensive/effectively impossible to get quickly in small quantities, you can run 100mbps and 1gbps Ethernet over "reasonable" lengths of single twisted pair using MoCA adapters plus coax->twisted pair baluns. Achievable cable length will obviously depend on EMI conditions, but I've had reasonable success with this method on twisted pairs in industrial robots.

GIGA G4201TM modems are built for exactly this, using the G.hn standard, over a single pair. I’ve been using these to avoid digging into walls to replace wiring — they claim to sync at up to 1700mbps and, even in the real world, I’m saturating the 1000BASE-T ports.

Re: ADSL works over wet string (2017)

#143

Post by edude03 » Mon, Dec 06, 2021, 12:31 AM UTC

zaphirplane wrote: post #128

edude03 wrote: post #115

Earlier quoted context omitted.

No, because 5g is a shared medium. It can deliver... 3 gigabit/s? or something like that? Let's say it's 10Gb. That's 10gb shared with everyone in the vicinity, which is not great especially in high density areas like apartment buildings. Furthermore, you still need to run fiber to the actual base stations anyway.

I think you are answering “is it better bandwidth per household”, while I am talking mb/S per dollar and ROI. Where I am 5g is same price as fixed broadband but faster for my plan. Are you paying and using 1g/s have no caps ?

Personally I am yes, but I know that's not the case everywhere. I get that you mean in terms of ROI, but that's ROI for the business, not for you the customer. So I guess what I'm getting at is, why would you suggest the thing that's better for the business but worse for you?

Re: ADSL works over wet string (2017)

#144

Post by Johnythree » Mon, Dec 06, 2021, 5:55 AM UTC

geofft wrote: post #43

giardini wrote: post #23

ADSL, being essentially a form of alternating current, will pass through an air gap. I was enlightened on this by an AT&T tech who pointed out that one of my ADSL lines had several breaks and could not carry DC but the ADSL signal still came through. The other line was dead so I was running essentially on one wire with an earth ground. Here is an interesting discussion: "Phone line with 1 broken wire still gets ADSL2…

In some sense, that's "just" radio. An antenna is a wire... it's sending a signal and picking it up from a very nearby antenna. Radio transmissions are all AC. (Arguably, the real insight here is that the very existence of radio is impressive / unintuitive.)

It's a differential signal using a center-tapped transformer to drive the signal. It's actually using three wires if you count the ground.

This means it's symmetrical about ground and thus cancels it's own radiated field (eg doesn't interfere with adjacent lines).

But with one side open there is still a path for AC, which is through the other side and using the ground return.

Re: ADSL works over wet string (2017)

#145

Post by Johnythree » Mon, Dec 06, 2021, 5:57 AM UTC

Terry_Roll wrote: post #94

hereforphone wrote: post #86

Earlier quoted context omitted.

What's DC? "Radio stations" communicate via alternating quantities (EM waves)

The telephone cable coming into the house is 50volts DC is not AC like a powerline. I know radio waves are just that, waves, its how things like noise cancelling headphones work. Different frequency's give you different ranges or distances for 1 watt, which is why you can bounce Long wave around the planet.

Phone lines use an AC signal which is superimposed on a DC current. The DC is used to power the phone.

Re: ADSL works over wet string (2017)

#146

Post by Johnythree » Mon, Dec 06, 2021, 6:01 AM UTC

jcrawfordor wrote: post #129

Terry_Roll wrote: post #108

Earlier quoted context omitted.

I wasnt taught that radio waves were to be considered identical to AC power down a cable but when thinking about it, they probably are identical with waveform properties and the difference being the medium they are travelling through.

The exact details become confusing and get into some physics details, but in practice radio frequency on a cable is basically an AC voltage that needs special care to not be lost to inductance and other effects. This is of course part of the general trend that DC through gamma radiation are in many ways the same thing. It's common parlance to say "DC component" to refer to any offset from zero in the AC waveform. So,…

The reason for your confusion is that the telephone exchange sends a constant Current, not a constant Voltage. There is 48V, but it's behind a 300+300Ohm relay which limits the current.

Re: ADSL works over wet string (2017)

#147

Post by Johnythree » Mon, Dec 06, 2021, 6:09 AM UTC

someperson wrote: post #8

codeflo wrote: post #5

That fact that this delivers 3.5 MBit/s really makes you wonder how many low speed connections out in the wild are literally broken cables that still have some amount of coupling somewhere.

Potentially apocryphal, but Telstra's copper cable network supposedly had its insulation made of paper, not rubber. I remember when it rained the curbside pits fill with water, causing slowdowns and frequent ADSL dropouts (until things dried out).

This not strictly true: The original pairs were paper insulated, but they were enclosed in a lead sheath which prevented water entry. Plus the cable was pressurised with dry nitrogen to keep out any water. Plus the flow of Nitrogen was monitored so that any pinholes could be detected before they caused a problem. Of course when Telecom was privatised all these quality control issues went out the window.

But there's a further point, the problem with moisture in the lines is the corrosion caused by electrolysis, which in turn is caused by the 50V DC on the lines. So even with modern plastic insulation, the copper would be corroded away by any electrolysis.

One last point: Rubber was almost never used as an insulator on phone lines.

Re: ADSL works over wet string (2017)

#148

Post by Johnythree » Mon, Dec 06, 2021, 6:15 AM UTC

ComputerGuru wrote: post #40

jcims wrote: post #30

Earlier quoted context omitted.

I know there are some telecom folks on here that may be provoked to correct me but pulp was standard before the advent of cheap plastic insulation in the 1950s on up. I live in the midwest and my brother is a lineman for AT&T. There is an astonishing amount of pulp-insulated phone line still in service today. In order to keep it dry, the conduit that the pulp lines are run through is pressurized to 5-10psi. Anyone th…

> I know there are some telecom folks on here that may be provoked to correct me Aka Cunningham’s law > Any kind of outage on the compressor or dryer I’m confused: isn’t a bigger concern any physical damage to the conduit anywhere in the run that is too large for the compressor to overcome? Or are we talking football-field-sized compressors here?

The gas flow on each line was monitored with flow gauges, so any increase could be attended to before it became a problem.

Re: ADSL works over wet string (2017)

#149

Post by Johnythree » Mon, Dec 06, 2021, 6:28 AM UTC

stefan_ wrote: post #77

jcims wrote: post #30

Earlier quoted context omitted.

I know there are some telecom folks on here that may be provoked to correct me but pulp was standard before the advent of cheap plastic insulation in the 1950s on up. I live in the midwest and my brother is a lineman for AT&T. There is an astonishing amount of pulp-insulated phone line still in service today. In order to keep it dry, the conduit that the pulp lines are run through is pressurized to 5-10psi. Anyone th…

The more you learn about this ancient cable technology the more absurd it becomes. We shower these fuckers with money but they would rather keep their paper insulated phone lines with permanent compressors and dryer running than braindead simple fiber. No wonder it is permanently broken and they can't keep a single 9 of reliability.

It depends on the country, but originally our Telephone Companies were motivated by Quality of Service. However all that changed when the companies were privatised and profits became their only concern.

Historically there was a continuous upgrade of equipment as the technology improved. Manual exchanges became automatic, step-by-step gave way to cross-bar which gave way to electronic exchanges. Analog phones were replaced with digital and ADSL. And had that steady improvement continued, ADSL would have routinely been replaced with Optical fiber.

What stopped the perpetual upgrades was the arrival Thatcher/Regan/Howard and the advent of Neoliberalism. Which meant that anything which provided a Public Service (gasp Socialism!) was completely abandoned. We are only now starting to realise the long term cost of their vandalism.

Re: ADSL works over wet string (2017)

#150

Post by Johnythree » Mon, Dec 06, 2021, 6:43 AM UTC

portportport wrote: post #137

Honestly, any ODFM system is so incredibly resilient they will work over nearly any medium. I've tested powerline ethernet airgapped, and it still faster than the WiFI on the embedded system I was testing.

And that is the problem with Ethernet over Powerline. Because the power lines are not balanced or shielded, most of the RF energy escapes and can cause serious interference to licensed radio services.

And of course, if the interference can get out, it can also get in. Which is why Powerline Ethernet can work just fine one day, then suddenly stop working.

Plus the big problem with any ODFM system is that it is incredibly intolerant of wideband interference, eg a series of sparks. The reason being that the band of ODFM channels are fed straight into an A/D converter without channel filters. So each time that wideband interference takes out the system, the modem has to stop and renegotiate each channel from the start.

To any experienced RF engineer, Ethernet over Powerline (or any ADSL system) is a disaster waiting to happen.