This is probably an MAU transceiver.
It must be plugged in a network card with an AUI connector (DB-15).

Like this on for example: https://en.m.wikipedia.org/wiki/Medium_Attach … thernet_NIC.jpg

It's more or less an older equivalent of today's SFP / QSFP ports.

I've never used one since most of my network cards have an rj45 connector

Nit-pick mode: it's a DA-15 connector, not a DB-15. The letter indicates shell size and DB is the size of a 25p serial or parallel connetctor.

On-topic: I have the exact AT-210T transceiver you link to there and can confirm it works exactly as you hope when connected to the DA-15 AUI port on an Ethernet card.

That said: I find these things fiddly, disconnecting easily, and it sticks out significantly behind an already very long case (which also increases chances you will bump it).

If you can't find an 8b ISA Ethernet card with UTP, I'd suggest going down the BNC route instead. You do need a bit more - not just the transceiver itself but also two 50Ohm terminators, two T-pieces to connect to your card and the transceiver - and a run of RG58 cable. Sounds more complicated, but the huge advantage is that it sticks no further out from the back of your case than the height of that T-piece and everything clicks solidly in place with BNC connectors.

3COM 3C503. very nice 8bit nic. works great in my tandy 1000. has BOTH rj45 and da-15 connector. they are very easy to get as well. not sure why you think 8bit nic with rj45 is rare.

BloodyCactus wrote on 2025-02-18, 13:37:

3COM 3C503. very nice 8bit nic. works great in my tandy 1000. has BOTH rj45 and da-15 connector. they are very easy to get as well. not sure why you think 8bit nic with rj45 is rare.

Am I living in backwards-land? There are four ebay results for "3COM 3C503", only one of which is an 8-bit card, it doesn't have an RJ-45, and the seller is asking for almost a hundred and fifty pounds for it. And no, "ISA NIC" does not give any more useful results, except for - as I already said - cards with a 15-pin port.

dionb wrote on 2025-02-18, 13:27:

Nit-pick mode: it's a DA-15 connector, not a DB-15. The letter indicates shell size and DB is the size of a 25p serial or parallel connetctor.

Yes, that's true. Further nitpick mode: RJ45 isn't the correct term either, it's 8p8c.

dionb wrote on 2025-02-18, 13:27:

On-topic: I have the exact AT-210T transceiver you link to there and can confirm it works exactly as you hope when connected to the DA-15 AUI port on an Ethernet card.

That said: I find these things fiddly, disconnecting easily, and it sticks out significantly behind an already very long case (which also increases chances you will bump it).

I was already thinking about using a DA-15 extension cable to solve this problem. As long as the wiring is straight-though, I don't see why that wouldn't work. The transceiver doesn't have screws on it, but I'll just tie it on with rubber bands or tape, or whatever.

dionb wrote on 2025-02-18, 13:27:

If you can't find an 8b ISA Ethernet card with UTP, I'd suggest going down the BNC route instead. You do need a bit more - not just the transceiver itself but also two 50Ohm terminators, two T-pieces to connect to your card and the transceiver - and a run of RG58 cable. Sounds more complicated, but the huge advantage is that it sticks no further out from the back of your case than the height of that T-piece and everything clicks solidly in place with BNC connectors.

I've actually already got all of that, my trouble is that I don't know how to, in the stupidest possible terms, "convert BNC to RJ-45". I want my 5160 on the same network as my modern PC.

might find them easier as "etherlink ii" lots of variants of it (some with bnc, some with just da15, some 8bit, some 16bit). they show up very often. maybe not heaps no ebay today, but they are not rare by any means. one with bnc+aui for 37$ right now.

Hm. I'm not familiar with 3COM 3C503 and always thought 8-Bit NICs are rare, as well..
Like the ancient NE1000, which was much less popular than its 16-Bit cousin, the NE2000.
Probably because the real NE2000 also worked in NE1000 mode.

With clones it's hit and miss, though.
Some can handle NE2000 drivers but are 16-Bit only and won't in 8-Bit slots.
Not even in 8-Bit slots on an AT motherboard.

Personally, I had 16-Bit 3Coms that worked in 8-Bit slots, but only after they had been configured in a PC with 16-Bit slot.
Otherwise, IRQ and EEPROM configuration didn't work.

Nowadays, I don’t really care about 10Base-T (RJ45) anymore.
I've accepted plain 10BASE2 network cards, as well. Anything NE2000 compatible is worth preserving these days.
RJ45 is obsolete, as well, sort of. The future belongs to W-LAN and optical ethernet, I think.

For my vintage networking needs I'm rather focussing on media converters.
Those that have 10BASE2 and 10BASE-T and AUI (?) ports.
But once they become unavailable, a PC with multiple network cards or USB NICs can take the role.

Typos fixed. 2x.

the nice thing about 3c503 is it has bunch of jumpers for config, makes it easy to setup its IO space (i even tested putting SRAM in the socket and making that window of sram available on my tandy 1000 as upper memory)

alfiehicks wrote on 2025-02-18, 13:58:

dionb wrote on 2025-02-18, 13:27:

Nit-pick mode: it's a DA-15 connector, not a DB-15. The letter indicates shell size and DB is the size of a 25p serial or parallel connetctor.

Yes, that's true. Further nitpick mode: RJ45 isn't the correct term either, it's 8p8c.

That seems right, I've read about it a few times.
Is that 8p8c term beeing used on an international basis or is it US only terminology?

Because, I remember that the RJ11 connector as used by phone cabling has another, more correct term, as well.
It's not being used were I live, though. RJ11 is exotic enough, already.
The term "western connector" is probably more widespread, at least among older IT people here.

By the way, in my country, FRG, the "RS-232 port" (aka EIA-232 port) often was being described as "V.24 port", as well.
In daily language, in the pre-Windows 95 days, IT people talked about the "V24" when working with serial ports. It even made it into books.

Though strictly speaking, both terms do refer to slightly different things, I think.
One is the protocol side, the other the electrical side, if memory serves.

Jo22 wrote on 2025-02-18, 14:03:

RJ45 is obsolete, as well, sort of. The future belongs to W-LAN and optical ethernet, I think.

I've seen versions of the transceiver I linked which have two fibre-optic ports instead of an RJ-45 - is that what optical ethernet is?

Jo22 wrote on 2025-02-18, 14:18:

alfiehicks wrote on 2025-02-18, 13:58:

dionb wrote on 2025-02-18, 13:27:

Nit-pick mode: it's a DA-15 connector, not a DB-15. The letter indicates shell size and DB is the size of a 25p serial or parallel connetctor.

Yes, that's true. Further nitpick mode: RJ45 isn't the correct term either, it's 8p8c.

That seems right, I've read about it a few times.
Is that 8p8c term beeing used on an international basis or is it US only terminology?

I don't know. I read it on an english-language Wikipedia article, so that shows how much I know.

BloodyCactus wrote on 2025-02-18, 14:12:

the nice thing about 3c503 is it has bunch of jumpers for config, makes it easy to setup its IO space (i even tested putting SRAM in the socket and making that window of sram available on my tandy 1000 as upper memory)

I like it! 🙂 Looks like a SB 2.0 in terms of form factor!

The jumpers are neatly aligned, too, probably using a common ground line on one side. (Edit: a common data line to a chip pin, I mean)
I can imagine that's good for attaching switches, for example (mounted on a backplate).

alfiehicks wrote on 2025-02-18, 14:21:

Jo22 wrote on 2025-02-18, 14:03:

RJ45 is obsolete, as well, sort of. The future belongs to W-LAN and optical ethernet, I think.

I've seen versions of the transceiver I linked which have two fibre-optic ports instead of an RJ-45 - is that what optical ethernet is?

Hi, yes. Optical NICs use a separate RX/TX cable pair.

Btw, about my comment about being RJ45 being obsolete..:
It's not yet. I do just think that with the increasing spread of optical fibre internet connections it becomes a bottleneck, eventually.
Like PhoneNet (RJ11), 10Base2 (BNC) had become an oudated or slow technology in the past.

So it's not unwise to consider installing optical ethernet outlets in the home/house at one point, just as well.
Because modern computers and game consoles demand for more and more bandwidth.
Who knows how much the next game consoles will need or how important "cloud" storage and streaming will be in near future.

Thus, I think, the vintage computers nowadays can just as well use their own little vintage network corner with old cabling.
Making everything RJ45 compliant nolonger is so important in near future, I mean.
The newer/higher-end CAT standards for copper cables use a different connector, anyway.

As an alternative, a PC or network "media converter" can then be used to integrate that vintage network into modern network topology.
(There are older switches and hubs and routers which can help to build a bridge on the electrical side.)
That being said, using RJ45 natively on all computers is less of a hassle, of course.

alfiehicks wrote on 2025-02-18, 13:58:

[...]

I've actually already got all of that, my trouble is that I don't know how to, in the stupidest possible terms, "convert BNC to RJ-45". I want my 5160 on the same network as my modern PC.

It takes a transceiver, very similar to the one you linked to for AUI-UTP, but then BNC-UTP.

Alternatively if you can't find one of those for an acceptable price (they still sell them new for USD 130...) you can look for an old 10Mb hub which invariably has a BNC port and so acts as a transceiver:

One pitfall though: these days there's a market for leading Ethernet over 75Ohm (TV) coax passively using baluns. They can have BNC connectors and look very similar to a transceiver but most definitely don't work the same.

AUI has a locking plate specified on the female (NIC side) connector and two corresponding studs specified on the male (Xcvr side) connector.

When you slide the locking plate into engagement like you're meant to, the connection is extremely robust and cannot be knocked loose. Much more in fact than the flimsy POS plastic locking tabs on RJ45

dionb wrote on 2025-02-18, 13:27:

[..] going down the BNC route instead. You do need a bit more - not just the transceiver itself but also two 50Ohm terminators, two T-pieces to connect to your card and the transceiver - and a run of RG58 cable. Sounds more complicated, but the huge advantage is that it sticks no further out from the back of your case than the height of that T-piece and everything clicks solidly in place with BNC connectors.

That's an interesting topic! 😃
Speaking of terminators, there are two types.
a) normal one with the cap
b) the other one with the ground wire.

If we use same type (a) only, there will be noise on the medium.
That's one of the reason people had issues with Cheapernet so often; inadequate termination.
The one with the ground wire has to be installed at one outer end of the bus (the long cable).

Here are some links I've found useful:
http://www.tiplord.com/networking/thin.htm
http://d.pcnews.at/ins/pcn/095/001800/main.htm

Irrelevant, but fun to read:
https://en.wikipedia.org/wiki/EAD_socket

Tip: TNC connectors are an alternative to BNC connectors.
They look some but won't rotate. In my CB radio hobby, coaxial cables with TNC connectors turned out to be more reliable. They had less contact issues.
Might be worth a try. Good 50 Ohm RG58CU cables should work in either application (radio, network).
But H155 and other modern 50 Ohms coaxial cables with better specs might work as well.
Shops that sell ham radio stuff sould have them.

PS: There's something that comes to mind. It's perhaps superflous, but I think I should tell.
Very cheap coaxial cables consist of merely a very thin centre wire.
They're not very good, at least in the radio hobby.

They have reflections on the medium and cause a bad VSWR (reflected energy).
In the radio hobby, that's bad because the radio's transmitter will heat up unnecessarily.

To test such cables for reflections, radio amateurs or CB operators can use a network analyser like the NanoVNA or an old RigExpert AA-170.
The NanoVNA is very cheap and can be bought from various sources.
On the other side of the coaxial cable that is beeing tested a terminator has to be attached.
Aka an 50 ohm "dummy load", in radio jargon. An ethernet terminator will do just as well here for measuring.

Edit: Here are some tests/pictures..
Both cables aren’t being ideal by any means.
Ideally, the black cable should show a straight yellow line at the bottom.
Maybe the connectors have some corrosion or humidity ruined the cable, not sure.

But an standing wave (VSWR) with infinity on the beginning is definitely bad (red cable). It's like a short in RF application.
The reflections as shown would be a catastrophe on a LAN.
If such cables made it into circulation, it's no wonder that 10Base2 got such a bad reputation.

Disclaimer: There might be measuring errors.
NanoVNA uses harmonics for measuring higher frequencies.
If I had chosen a smaller range, maybe the results would have been more accurate.
This is just meant as a demonstration.

Never had first hand experience with BNC networks (i'm a bit too young)
But just looking a the "BUS" network topology, the performance should decrease rapidly with the number of systems connected.
All the stations are sharing the same ethernet collision domain and CSMA/CD would throttle the packet rate quite a bit.
Am i correct ?

acl wrote on 2025-02-18, 16:50:

Never had first hand experience with BNC networks (i'm a bit too young) But just looking a the "BUS" network topology, the perfo […]
Show full quote

Never had first hand experience with BNC networks (i'm a bit too young)
But just looking a the "BUS" network topology, the performance should decrease rapidly with the number of systems connected.
All the stations are sharing the same ethernet collision domain and CSMA/CD would throttle the packet rate quite a bit.
Am i correct ?

Interesting thought!
Same time, though, it makes me wonder how PhoneNet/AppleTalk managed to be so succesful.
80s AppleTalk was chatty, the wiring was much more simple (phone wire), had used AF transformers and the speed was 115 KBit/s 230 KBit/s. Edited.

Edit: https://en.wikipedia.org/wiki/PhoneNET
AppleTalk software was also available to IBM PC running DOS/Windows 3.
There's even an ISA-based LocalTalk network card that's being supported.
Windows 95/NT4 and up can do AppleTalk protocol, too, but there's no modern PC hardware for classic LocalTalk/PhoneNet.
Media converters or Macs can do the bridging to classic networks, though.

Edit: Here are some more tests/pictures.
This time I've used an ordinary BNC ethernet terminator.
It's just a carbon resistor and has less self capacity/inductivity.
Ideally, the curve should not change much if a good quality coaxial cable is inbetween.

The red ethernet cable has lots of peaks/mountains. It looks okay, because measuring the range is 1GHz.
But on an ethernet it's bad if there's a peak every so often.

The black cable (old worn CB radio cable) has peaks/mountains, too, but they appear to be less sine-like.
The reflections are in no way good, but appear less "symmetric" (equal) which is better.

Personally, I would use neither of these cable for my ethernet here.
I've just taken them for demonstration purposes.
A straight line for a curve as shown with the terminators is being recommended.

Typo fixed.

PS: Yellow line is VSWR, green line is Smith diagram.

acl wrote on 2025-02-18, 16:50:

Never had first hand experience with BNC networks (i'm a bit too young) But just looking a the "BUS" network topology, the perfo […]
Show full quote

Never had first hand experience with BNC networks (i'm a bit too young)
But just looking a the "BUS" network topology, the performance should decrease rapidly with the number of systems connected.
All the stations are sharing the same ethernet collision domain and CSMA/CD would throttle the packet rate quite a bit.
Am i correct ?

on bnc, they all talk at once so collisions get higher the more connections you have, and collision used to be the nic would go into a short random wait and try again.

i hated running bnc for lan parties!

Topologies all have their pros and cons, I suppose.

https://www.webopedia.com/reference/network-topology/

The cable internet connection is a bus, too.
It uses thick coaxial cable medium that's being shared among all participants.
Coaxial cable has shielding, also, which twisted-pair doesn't have by default.

Edit: Another picture/test.
Here's a ring of coaxial cable, the characteristics are "ok".
There are still some reflections, but over an 1GHz range.

That's how the red network cable should have been, I think.
The "waviness" isn't that prominent here.

Disclaimer: This is just meant as a demonstration, to give an idea.
Ideally, the cable ring should have been unrolled, maybe.