Low pass filter target frequency for a mixed signal frequency synthesizer
The PLL is working fine without the Mixer and LO? What is the bandwidth of the bandpass filter that you're using? Since the VCO and DDS tune over a couple of MHz, I suspect that anything that you're introducing with that will be invisible to a 1 kHz loop filter bandwidth. I'd propose two things to help debug this. First, use the simplest passive loop filter that you can, a simple 2nd order would work fine, as you've got no locktime/phase noise requirements. that will simplify the system. Second, look at the output of the DDS on a spectrum analyzer to see that the spurious level looks like-You could have some close in DDS spurious causing jitter.