I am using two Nucleo-STM32WL33 board, one as a transmitter and one as a receiver. The transmitter sends two messages in ASK modulation and the receiver records the messages in IQ sampling mode.
Below is a visualization of the IQ samples time series.
The logical 1s are quite clear and all have a similar amplitude, however for some reason there seems to be a sinus-like subsignal whenver the transmitter sends a logical 0. I would have expected an amplitude close to zero, like seen during the time frame between the two messages or after the end of the second message.
There is a distinct 1/4 period phase shift between I and Q component, so its clear to me this has something to do with the IQ modulation itself. But what is causing this sinus subsignal? Is it caused by the receiver or transmitter? How can I remove it?
