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Anyone out there other than me old enough to have run a 10base2 network in their home? My first computers 2 computers when I was in high school I connected together with a 10base2 with 50 ohm terminators and all that. My mom wasnt happy as I literally knocked a hole in her wall without asking her.

This was back when the internet was still fairly new so you would get on with 1200 baud modems to a BBS that would give you a piggyback onto the internet which you might be lucky to get access to for 30 - 60 minutes a day.

10base2 network card attached for prosperity.

@Science

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@lucifargundam

Yea I saw this. though it doesnt even connect to your computer to get you 10base2 access. It just converts from one obsolete standard (10base2) to another (10baseT)

@Science

@freemo @Science
10b2 >> 10bT >> rj45 >>fiber? :D is that a thing? How many more adapters do we need to human-centipede to make it work?

@lucifargundam

Would kinda be fun to find some old school super ass slow networking connectors and chain them them through a series of adapters for each generation till you get to a gigabit network, and then run it on a modern network :)

@Science

@freemo @Science I did 2mbit arcnet coax before ethernet, does that qualify?

@freemo Hehehe, never had them myself, but I've seen them at work before. Especially handy for the big places. :)

How come this kind of networking isn't in use anymore? Isn't it much easier cabling-wise?

@trinsec well aside from being much slower (it slows down the more computers you have on a ring) it is also much more finichy on a few accounts. 1) any computer that is at the end of a chain needs a terminator, without it everyone on the wire cant connect. 2) if any one point in the network fails then the entire network fails, or atleast everyone on that loop/chain.

@freemo @Science we used it to connect 2 pcs in our student dorm and do airbattles against each other ca 1990/2.

@freemo @Science and i probably have a box w bnc connectors in the attic, if not the cards themselves.

@amerika

Yes my very first modem was 1200 baud. Though I think at the time technology had advanced to 9600 baud, but I was a poor kid.

@Science

@freemo @Science

I remember those USR HSTs (19.2kbaud) and how all of us wanted one, but they were like $1100. And the Telebit modems were even better.

@amerika

Back in my day they were coming up with new faster modems all the time. The holy grail was the 56K modems that were pretty much the last and fastest before things like DSL started to become the norm. Still used your phone lines and sent audio, but they were faster and would let you talk on the phone at the same time.

@Science

@freemo @Science What is the shield connected to? I vaguely remember breaking a network card's transceiver by dropping scissors in a way that shorted the shield of the BNC connector to the computer's chassis (the card that broke was, weirdly enough, the one where that happened and not the other one on the network). I expect that the shield cannot be connected to ground via low-impedance anything, because this would create a ground loop. So, is it galvanically isolated from the rest of the computer or is it connected to something?

@robryk

Ideally the shield should be connected to ground as in any coax configuration. However even if it werent connected to ground it would work, so its possible you had some sort of a cheap card that was wired weird. Also possible there was a bias-t hooked up to inject power into the coax, in which case the shield should have still been counded but could possibly explain the problem you had if it was wired wrong.

You may have had a ground loop going on, but that should only happen if, again, your home or computer is wrired incorrectly.

@Science

@freemo @Science

At that time the house in question was essentially wired as TN-C, with the E-N split happening in outlets. I don't think there was a way to get different PE potentials in different places, unless one was totally disconnected (which I doubt -- I think we actually measured PE-N resistance as part of figuring out how everything is wired up). So, dunno what could have been wrong.

Maybe the adapter was weird, but if someone cheaped out, I'd expect them to do less galvanic insulation and just ground everything that's vaguely ground-shaped.

Also: how was this supposed to work when computers it connected just had different ground potentials? Coax had something like 100m max distance it was supposed to be used for 10Mbps connections over, and that can easily span buildings, which could then be on TT or be on TN but on different power substations.

@freemo

I just saw an application note for 10base{2,5} transceivers and it shows transceivers with complete galvanic insulation (well, apart from a 1MOhm resistor between shield and ground): bitsavers.trailing-edge.com/co

It also states that the 1MOhm resistor is mandated by spec to discharge static electricity, so I infer that spec requires galvanic insulation.

@Science

@robryk
Not having a grounded shield is also a bit of a safety hazard. 10 ohm resistor between shield and ground seems odd to me.
@Science

@freemo

Not sure if you misread or mistyped: it was 1 megaohm.

I really don't see how you could avoid having a ground loop through the network cable otherwise, at least for runs that span buildings.

Re safety: do you mean that one of the transceivers could be broken and connect the shield to something?

@Science

@robryka

I mistyped.

Why do you think a ground loop would occur when spanning buildings? The neutral line in a power line is grounded at many points in each building, usually this doesnt cause a problem.

Yes the safety issue largely has to do with shorts to the shield.

@Science

@freemo

Why would it need to be the same PE line? If the buildings are on TN-S (which is rare), then their ground/PE is connected to grounding rods, water pipes, and nothing else. If they are on TN-C, then their ground/PE is connected to the neutral line from the grid: but they might be on different substations. In both the TN-S and TN-C with different substations case, PE of both buildings is grounded (hopefully with some reasonably low resistance to ground[1] on the order of tens of ohms), but the only way they are connected with each other is via the soil, so the resistance between PE of one and the other building is of the same order of magnitude as the resistance-to-ground of either. This is way higher than the resistance of the shield in a coax cable, so if the actual ground potential under the two buildings is different, you'll get some current through the shield.

Am I mistaken in the way I imagine this somewhere?

[1] I use a model where we have some "true" ground and grounding rods have a connection to it via some resistance. I don't know when this model breaks down.

@Science

@robryk
Physical earth groubds according to electrical code must always be bonded, as in electrically connected. Across buildings this occurs through the neutral line. So their electrical connection is not limited through the earth but are also connected through a wire.
@Science

@freemo

Sorry, s/TN-S/TT/ in my previous post (and TT is rare enough not to mention anywhere I lived, so ignore it).

How does this work for areas served by different substations? Are the neutrals of different substations connected with each other?

@Science

@freemo

Ah, I guess they are anyway connected in practice via the water mains.

@Science

@robryk
Yes even substations have their grounds bonded. All neutrals everywhere have groubd rods every few poles and are bonded across substations. Grounds are always bonded.
@Science

@robryk

Grounding via water mains is no longer up to code. You must use a ground rod these days. They are bonded through a physical wire.
@Science

@freemo

Sure, but you're _also_ required to bond with water mains ttbomk, and that was the most obvious way to convince myself that grounds of adjacent substations must have a low-resistance connection.

@Science

@robryk

Attached you will see a picture of a transformer which could represent a substation. Notice how all the grounds are electrically connected and they even add an additional bonding wire (this is because neutral can be disconnected via fuse and you dont want this to disconnect your bonding).

@Science

My first network at home :-) Was a gift from someone I helped.
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