I was trying to simulate AD9914 using ADISIMDDS tool with 3.5GHz as ref signal. According to datasheet narrowband spurs are -95dBc at ±500 kHz offset. But when i select a frequency 874.9MHz, i get a spur at 875.3MHz (f2-3f1) of -60dBc. So it means that we can not get narrowband spurs -95dBc near about this frequency. I was planning to use Tunable filter after DDS to clean up the wideband spurs as my spurs requirement is better than -90dBc. But I can not remove these narrowband spurs. Any suggestion?