Is this a FDX or HDX bidirectional link? Is it Async or Sync? Baud rate? 1200?
You ought to make the bus balanced differential and controlled impedance to minimize reflections. This might be 200 to 240 Ohms differential impedance for twisted pair.
You will need a CM choke at each end.
Your impedances are 10 Ohms from the driver, which is too low. That gives a stronger Tx signal but worse SNR at far end and reflections at Tx end.
Due to frequency loss gradient on long haul, baseband NRZ has more ISI than BiPhase which shots the BW up to the clock rate.
You can get much better speed and SNR using a PHY magnetic port adapter, such as used in telephony , Ethernet etc but tuned for your cable. (UTP, CATx or whatever) what do you have?