Sending PPM values through trainer port


I'm working on a project that involves sending PPM values generated by Arduino to a transmitter.The transmitter I'm using is an HK T6A V2 which has a trainer port .I have been trying to send PPM values through the serial-in pin of the port to control my quad.

1.The PPM values read from the PPM-out pin falls within acceptable range of the PPM values I'm generating using Arduino.

2.I had cut-out the throttle control while trying to control the quad through the PPM values sent serially using the left knob of the transmitter.

3.I'm sending values from MATLAB to Arduino where PPM is made using the received values.

However,the setup doesn't seem to be working.I need to send PPM to control my quad when I'm not using the joysticks for control.

Please let me know if my method is incorrect or if my setup is faulty.

Thank you.