Was the old 10base2 coax ethernet standard a transformer isolated bus?

[e100]

This was yesteryears technology so my Google searches haven't been turning up much.

According to https://www.brainbell.com/tutorials/Networking/10Base2.html# up to 30 nodes were supported on a single bus, and I remember seeing bulky transformers on interface cards that plugged into your computer.

Was each node effectively a transformer sitting across the coax, or was it more complicated than that?

Are there any multi-drop transformer isolated communications systems still alive today? Seems like an ideal solution when you want to connect a bunch of stuff without having to deal with ground loops.

 

[fordem]

As I recall it, no, there was no isolation between nodes, I've had at least one incident where an electrical fault took out one system in it's entirety and all the NICs in the rest of the network - the fault by the way, was external to the system it took out.

[Miyuki]

This is how isolation was done
https://mouser.com/pdfdocs/discrete-tnt.pdf

So transceiver sit at coax level and you isolate the digital side
Makes sense, you do not want load from plenty of transformers and possible signal issues.

So totally opposite way that today twisted pair ethernet using
If you need insulated nodes you can get reinforced insulation transformers for ethernet

[e100]

This is how isolation was done
https://mouser.com/pdfdocs/discrete-tnt.pdf

So transceiver sit at coax level and you isolate the digital side
Makes sense, you do not want load from plenty of transformers and possible signal issues.

So totally opposite way that today twisted pair ethernet using
If you need insulated nodes you can get reinforced insulation transformers for ethernet

So presumably it was the DC-DC converter that made the modules unusually large.

[mikeselectricstuff]

It was isolated - the card has an isolated DC-DC converter and pulse transformer. These connect to a transceiver chip ( usually DP8392) that connects to the coax.

[mikeselectricstuff]

So presumably it was the DC-DC converter that made the modules unusually large.

they were typically a 28 pin DIP package about 10mm high, 5V to -9V if I recall correctly

[voltsandjolts]

Are there any multi-drop transformer isolated communications systems still alive today? Seems like an ideal solution when you want to connect a bunch of stuff without having to deal with ground loops.

Manchester over multi-drop tranformer isolated comms:
https://en.wikipedia.org/wiki/MIL-STD-1553
Its used in systems 50kft above ground and 30kft below ground.

[amyk]

If you are talking about the standard, look at the standard itself - from 802.3-2012

10.4.2 MAU electrical characteristics
10.4.2.1 Electrical isolation
The MAU must provide isolation between the DTE Physical Layer circuits and the coaxial trunk cable. The
isolation impedance measured between any conductor in the DTE Physical Layer circuitry and either the
center conductor or shield of the coaxial cable shall be greater than 250 kΩ at 50 Hz, 60 Hz. In addition, the
isolation impedance between the DTE ground and the coaxial cable shield shall be less than 15 Ω between 3
MHz and 30 MHz. The isolation means provided shall withstand 500 V ac, rms for one minute.

[joeqsmith]

I designed and built a reverse print server that supported coax.  It allowed me to print from my old test equipment to an Ethernet  printer.   Used a 6811 and I wrote the stack in assembler.  Much of the heavy lifting was done with an FPGA.

Attached are datasheets for the parts I used in the design. 

************
Added a few pictures of it.

[David Hess]

The previous posts covered it so I will summarize; each node was isolated from the coaxial cable by isolating the entire transceiver on the digital side and providing it with an isolated power supply, usually including +9 volts for some reason.  This included leaving the coaxial shield connection floating as well but I think one node was suppose to ground the coaxial shield.

Isolated RS-232/RS-422/RS-485 transceivers work the same way.