Back in the 1990s there were at least three commercial TNCs that implemented 2400 bits per second.
- ? which is an optional board for the MFJ-1270 or MFJ-1274.
- ? .
- ? .
They all used the XR-2123 modem chip.? Now it is done with software.
The "B" version is known to be compatible with the MFJ-2400.