I am transmitting a barker 13 signal with approximate -3 dB beamwidth of 7 MHz. The signal is transmitted on RF frequency of several GHz.
When I have configured the the FIR coefficients and the rest of parameters (sampling rate is 60 MHz), I have the following problem while looking on the AD9361 output using spectrum analyzer:
1. There are FIR replicas the are shifted N*60 MHz (N starting from 1). The first replica is about -30 dB lower than the Tx signal and the rest are even more
How is it possible to filter these replicas?
Why the analog LP filters that are placed after the DAC don't filter these replicas?
Do you advise to change the analog LP filters coefficients (in current AD9361 driver there is no direct access to these filters parameters)?
Thanks in advance.