Look at the receiver output with a scope and see how much noise is present and whether you expect a UART to clock in the data properly. You see, it takes only something with the appearance of a start bit to get the UART started shifting in bits.

A UART's NRZ plus start bit encoding scheme is not a good choice for ASK, although some folks have employed different encoding schemes at a higher level that account for the UART's start and stop bits and then just use the UART to clock out the bits.


And most likely bit-banging at the transmitter too. Bit-banging transmit and receive are done when internal peripheral subsystems in incapable of generating the waveform of the encoding scheme chosen to suit the RF link's characteristics.