How to create cheap four wires untwisted ethernet cable for short distance

[neonix]

You don't have to buy UTP eight wires cable to create local LAN network.

You can use any wires you find, with 100BASE-TX standard, and IEEE 802.3u-1995 specification.

I don't know what is maximum distance, but it work in short distance in home bulding, between rooms. If you have modern switch/router you don't have to care about crossover.

https://www.reddit.com/r/HomeNetworking/comments/zddylt/ethernet_over_untwisted_phone_lines_it_works_how/

[gadget42]

after glancing frequently in the garbage bins most everywhere, we have a never-ending supply of cat5 and cat6 raw cabling of many various lengths. even pieces that had somehow been physically damaged(rodents?) and were used to pull in new cabling are fine to cut down for short runs. just make sure to put new ends on them and always mark and test them before usage(keeping good documentation/notes is wise, ymmv).

[CentralWare]

I don't know what is maximum distance...

Ethernet copper is rated based on the thickness (guage) of the copper and the shielding of each strand onto the next.
The cheapest method of room-to-room IF you need two or more connections is to share a single 8 strand CAT5 which is split into two separate channels simply based on which wire goes to which pin.

Pins 1, 2, 3 and 6 are channel 1, the others are channel 2.  You'll get two 100Base-T connections for up to 30~50 feet depending on the cable gauge.
Any faster than 100mbps and you'll get cross-talk over 10~15 feet; again, depending on the cable itself.

There are plenty of docs online that define CAT5/6/7/etc specifications, wiring and pin-outs, cable length and gauges, etc.

[gadget42]

poked around a bit and this was decent to get folks started:
https://electrouniversity.com/how-to-test-ethernet-cable-with-multimeter/

multimeter testing is fine for the home hobbyist but if you plan on a more professional endeavour(install/testing/troubleshooting/etc) then a more purpose-built tester is warranted.

right now the Klein Tools VDV526-200 Cable Tester is fairly popular and in the $50-$60 range currently(at that bezos place)

[CentralWare]

Evenin' @Gadget42!
I'm cheap   Here's a $14 tester that does everything you need to determine if COPPER is aligned properly...  whether or not it's GOOD copper and/or shielding is another story.