The AD9361 Data sheet clearly states that there is a tunable channel bandwidth up to 56 MHz. I'm trying to find out how that number was arrived at, specifically for the transmit chain. The DAC outputs are followed by a Baseband LPF and a 2nd LPF. One of the User Guides states that: the TX BB LPF is programmable to 32 MHz ans is typically calibrated to 1.6 times the BB channel bandwidth, and the TX 2nd LPF is tunable to 100 MHz and is typically calibrated to 5 times the baseband channel bandwidth. These both calculate out to 20 MHz BB bandwidth, or 40 MHz RF bandwidth. Perhaps you can go beyond "typical" in your frequency usage, in which cast the 32 MHz LPF would appear to limit you to 64 MHz RF bandwidth. So, how was 56 MHz arrived at? Is there something in the digital interface and filtering? Is the signal degraded when going beyond typical to 56 MHz? Or is 40 MHz really the practical limit for this part?