Was the old 10base2 coax ethernet standard a transformer isolated bus? - Page 1
Forum section: electronics / projects

author: e100
author_rank: Frequent Contributor
timestamp: March 19, 2021, 10:16:36 am
content: This was yesteryears technology so my Google searches haven't been turning up much.According tohttps://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.

author: fordem
author_rank: Regular Contributor
timestamp: March 19, 2021, 10:41:14 am
content: 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.

author: Miyuki
author_rank: Frequent Contributor
timestamp: March 19, 2021, 10:47:34 am
content: This is how isolation was donehttps://mouser.com/pdfdocs/discrete-tnt.pdfSo transceiver sit at coax level and you isolate the digital sideMakes sense, you do not want load from plenty of transformers and possible signal issues.So totally opposite way that today twisted pair ethernet usingIf you need insulated nodes you can get reinforced insulation transformers for ethernet

author: e100
author_rank: Frequent Contributor
timestamp: March 19, 2021, 11:37:42 am
content: Quote from: Miyuki on March 19, 2021, 10:47:34 amSo presumably it was the DC-DC converter that made the modules unusually large.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 19, 2021, 11:39:27 am
content: 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.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 19, 2021, 12:00:48 pm
content: Quote from: e100 on March 19, 2021, 11:37:42 amthey were typically a 28 pin DIP package about 10mm high, 5V to -9V if I recall correctly

author: voltsandjolts
author_rank: Unknown
timestamp: March 19, 2021, 01:19:41 pm
content: Quote from: e100 on March 19, 2021, 10:16:36 amManchester over multi-drop tranformer isolated comms:https://en.wikipedia.org/wiki/MIL-STD-1553Its used in systems 50kft above ground and 30kft below ground.

author: amyk
author_rank: Super Contributor
timestamp: March 19, 2021, 01:25:20 pm
content: If you are talking about the standard, look at the standard itself - from 802.3-2012Quote

author: joeqsmith
author_rank: Super Contributor
timestamp: March 19, 2021, 01:33:05 pm
content: 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.

author: David Hess
author_rank: Super Contributor
timestamp: March 21, 2021, 05:08:51 am
content: 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.