According to specification, the AD9361 can support 56MHz channel bandwidth. But in fact when we tried to modulate signal with 45MSPS QAM64 modulation, we find that there is attenuation at the edge of spectrum. We are not sure if this is related to the AD9361 configuration. Any help?
Did you use the filter wizard to design transmit and receive FIR filters? If so, what were the settings used?
We are not using the filter wizard for the design of the filters. Our signal is about 27 MHz in the baseband, so wider than the 20 MHz of the programmable FIR. For this reason, we bypass the programmable FIRs and use only the HBs and analog filters after the DAC. The HB settings are (HB1, HB2, HB3)= (1, 2, 2).
The half-bands are not perfectly flat over the passband which will cause inband attenuation. The FIR's main job is to provide a maximally flat passband. Using the filter wizard will design an FIR to compensate for this droop and setup the front-end analog filter correctly.