Shouldn't the termination on 10base2 be 50 ohms, not 500 ?

EDIT: WIKIpedia seems to match up with my memory, FWIW. https://en.m.wikipedia.org/wiki/10BASE2

Forget that, should be sleeping rather than misreading you.

Sorry

Does dmesg print anything when you modprobe the card?

It might be configured for aui instead of bnc.

I've decided to use my oscilloscope cable with 1x BNC

Very thin, poor cable. Lots of losses. It's something like RG-174, I believe.
The scope doesn't mind cable quality because it's high impedance, I think.

Since I'm doing this on a budget (the whole cable costs more than the setup is worth)

I'm so tired of that mindset. Of valueing everything through money. 😮‍💨
(To people like me this comes over as "Hey, everyone! I'm a penny pincher and I know exactly and intentionally that I'm working with a garbage setup but please help")

By that logic, in reverse, why should anyone feel comfortable to waste time to help here?
Everyone's life time is very precious, too, isn't it? 🤷‍♂️
And if so, doesn't that make some feel degraded, kind of?

(Please don't take it personal, I know it wasn't meant in a bad way and there are many people who were raised with that mindset.
And that's just exhausting. Experimentation is another thing and alright, I think.
But asking for other people's help or advice because money has top priority is so.. oh, never mind.)

I will try to replace it with an standard TV antenna cable and add the resistors for termination.

Hi, that's 60 ohms or 75 ohms, I believe. Might work, not sure.

Just an idea: For 10Base2, good RG-58CU cable is being recommended, I think.
It uses lots of copper wires instead of one stiff, single wire.
A shop which has CB radio stuff might help. The truckers still use CB, for example. Maybe they can help, have spare cables.

CB radio coaxial cables traditionally used RG-58 and PL connectors and were mass produced.
Then it merely needs a PL to BNC adapter. Male PL plug is PL-259, the Female PL socket is So-239. UHF connector is a synonyme to PL connector, too.

Ideally, the coaxial cable doesn't have much reflections (flat curve; nanoVNA is a cheap tool to check that).
A bit more information can be found here: 8-bit ISA Network Cards with DB15 connectors?

PS: The RG norm is just a loose specification, it says little about quality.
So one RG-58 cable can be totally different to another one.
Especially good shielding is hit and miss. The C and U define the material used.

Edit:

Now, the problem is with the 3com card.
I have no idea what's wrong with it, but the DOS diag utilities can't find it on any IRQ.
Even after reserving IRQ 5 for ISA in BIOS and turning off all extra devices (sound, FDC etc.) in BIOS I still can't get it to dected properly.

That's weird, indeed. Maybe the DOS utility was made for another chip revision?
It's just a guess, not sure. I'm no network card expert, either. 😅

kotel wrote on 2025-05-16, 05:01:

I got an 3com etherlink II

You are aware that this particular card is not pure I/O like many other ISA network cards (NE2000 and Etherlink III for example)? It uses memory mapped buffer access. Linux Ethernet HOWTO explains this, and while the card can be made to work in pure I/O mode it's slower and not the default behaviour. Long story short the memory mapped access must be R/W and thus not shadowed by mobo or used for UMB. So these cards are best for 286 and early 386 systems, anything else requires careful setup to get them to work properly.

If you want to build coax to TP router box I would suggest:
a) Not using any Windows for that, Linux is your best option, preferably something old and thus with low RAM and CPU requirements. Text console only since it'll probably work headless most of the time.
b) Consider Etherlink III or more common NE2000 network adapters for this purpose, this is more CPU heavy but easier to get working, and what else is that CPU going to do anyway.
c) After you are done testing I also recommend a proper 50 ohm coax cable with proper terminators. Yes coax can be very forgiving on short spans with just a few hosts but at the same time when you do get problems it's difficult to figure them out. From personal experience the cheap T-splitters can be a nightmare to work with.

Oh, yes! It's a sibling to the 3C500/3C501 card! It's an early design, like the unrelated WD8003!
I read about they a few days ago, they were supported by ancient Unix versions.
I totally forgot about this! I'm such a fool! 😅

https://www.os2museum.com/wp/emulating-etherlink/
https://www.os2museum.com/wp/1988-networking-386-xenix/

Edit: http://insight.actapricot.org/insight/kbase/i … nix/ipb3150.htm