I am trying to design a communication system that will send data signals over a 400V DC voltage line by using line transceivers. I attached the LTspice schematics below. The transformer is for providing isolation between 400VDC and the transceivers.
The problem is the size of the inductor shown inside the red circle. If I decrease the inductance value, the square wave coming from the A-B input loses its shape and peak voltages occur. This causes false high voltages at the RO output of the receiver side. However, since the DC current is 3.5A at the power line. The required inductor size increase enormously with the inductance value in order to prevent saturation. In the attached plot the simulation results are shown while using 200 uH inductor. You can see the problem. So, how can I calculate the required inductance and is there any other configuration for this system that works with a smaller inductor?
The "DK" input shown in the left of the schematic is similar to the picture I attached below. I did not show the generation part of that "DK" input at the question for decreasing the picture size.
The LTC2862 transceiver outputs the modulated signal (second plot of the below picture) from its A-B outputs. That modulated signal travels through the transformers and 400V DC line then comes to the A-B input of transceiver at the right side of the schematic. RO output of this gives a modulated signal (but only 0V and 5V, like the green plot at the picture I attached at the question) according to the voltage at the A-B inputs. Then low pass filter removes the 80kHz carrier signal and the data sequence is formed and received just like the first plot at the below picture. As I know this is amplitude modulation but If I am wrong please correct me.