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Expanding - Hopefully

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dunkemhigh:
Pneumatics. No-one else is using that air vent so you could stick a speaker at one end and microphone at the other and play modem warbling sounds. Bandwidth not so hot, but think of the YouTube videos you could do!

EEVblog:

--- Quote from: mikeselectricstuff on July 18, 2021, 10:41:45 am ---I'd imagine there would be plenty of spare pairs in those multicore phone cables running down to the MDF room

--- End quote ---

I only have 12 or so spare pairs in my lab.

mikeselectricstuff:

--- Quote from: EEVblog on July 18, 2021, 12:31:42 pm ---
--- Quote from: mikeselectricstuff on July 18, 2021, 10:41:45 am ---I'd imagine there would be plenty of spare pairs in those multicore phone cables running down to the MDF room

--- End quote ---

I only have 12 or so spare pairs in my lab.

--- End quote ---
So if they come out in the MDF room, that saves the hardest part of the cable run, through those full-up floor holes.

Fubawuba:
As suggested before, have a look at fiber optical connections. It's more affordable than you think.
You could for example use 2x media converter (RJ45<->SFP Cage) + 2x SFP(+) module, + fiber cable.

The distance is not a problem and the fiber cable (it's usually a twin cable with TX+RX fiber) is very thin (usually +/- 2mm sleeve per fiber) and quite flexible, but it's also a bit fragile (bend radius, thin sleeve, etc.), so you might want to put it in a PVC pipe or tube for additional protection.

You can find fiber twin-cable even on large spools for extra long length, but attaching LC connectors your self is complicated (LC connectors are the most common type of fiber connectors for home & garden use :)) so it's better to use a prefab cable.

Common combinations:
For short range (max range <550m, but also limited by module RX sensor sensitivity and TX output power) you can use multi-mode (850nm) SFP(+) modules with OM3 or OM4 fiber with LC connectors.
For long range you can use single-mode SFP(+) modules (usually 1310nm) and OS2 fiber with LC connectors.

You can find very affordable SFP's in the 100M-10G range.

Example:
2x 1G TP link media converter + 2x FS.com 1G SFP module of choice (for example 1000BASE-SX) + OM4 fiber twin cable with LC connectors (TX+RX)

With the fiber cable in place you can always upgrade to higher speeds by replacing the media converters and SFP modules (as long as it has LC connectors and is suitable for the fiber you used).

In any case this kind of solution will be more reliable and will have a faster connection than any kind of wireless connection (especially in a building full of metal) and it's easier to handle than RJ45 network cable (with a prefab cable, in your situation).

Monkeh:

--- Quote from: EEVblog on July 18, 2021, 06:06:00 am ---Inspection of the cable run.



--- End quote ---

So approximately 15m to that cupboard. About 3.4m per floor (200mm per block x 17), or 16m down to the correct floor. I reckon about 25m to the 90 degree on the duct, maybe another 10m from there to the bunker wall. Your 70m guess isn't too far off the mark. I'd guess 80m for a real cable run. Copper should be fine, although I doubt they'll want to just run it on top of the duct - but that route will probably be fine to follow.

I would still run fibre, but that's me. Also, as to the 'box on both ends' argument - you may as well have wifi down in the bunker, so no extra box needed down there (APs with SFP slots for fibre are readily available).

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