Need some feedback on techniques to make an old analog bus work with bidirectional data(half duplex is fine) at speeds upto 256kbps
The cable itself is a shielded twisted pair with a nominal impedance of about 50 Ohms. It's wired to various points in large buildings in anyway the installer felt was optimal (this includes daisy chaining, branching off into a star at a daisy-chained node etc). I believe it was used to pass audio and/or very low bit rate security data up to 500meters in length
Some of things I considered include:
1. A variant of 10Base2 at a lower data rate. The manchester encoding and csma/c(d/a) shouldn't be too hard to implement but the uncontrolled bus cabling worries me. At 256kbps(kHz) and some controlled slew rate the reflections and signal integrity shouldn't be too bad?
2. Restricting bandwidth to 40kHz or even 20kHz and increase bits/symbol by using QAM. This is not my preference because of the complexity of implementation unless if I can find a single chip SoC. Maybe there are bits and pieces of the old school v92 soft modem libraries I can re-purpose
3. Adapt Power line Communication techniques like G3-PLC
There is not much I can do to change the cabling as it's an existing installation. There won't be anything else on it, if it helps with reflections I can terminate it at each and every node. These cables are by and large interference free because of the shielding and differential signaling
Any thoughts/stories that you can share are most welcome. Thank you.
EDIT: The solution is not specific to one site, the wiring is different in each site and there about two dozen sites all up.
EDIT: There can be between 12 to 15 nodes on each bus