I've now added another crystal section to the notch filter to get a notch depth of nearly 65dB. The notch filter now has 6 crystals.
Here's three phase noise plots using the notch filter at 9.828MHz. The top trace (pink) is the phase noise of an Agilent E4433B vector sig gen. This has really poor phase noise on the HF bands as you can see in the plot below. It's approx -103dBc/Hz across the whole 10kHz span.
The cyan trace is the phase noise of one of my Marconi 2019 sig gens. This sig gen has quite low phase noise and shows about -141dBc/Hz at an offset of 4.5kHz.
The yellow trace at the bottom is the MMIC/crystal oscillator and this shows -163dBc/Hz at 4.5kHz offset. This oscillator doesn't quite sit in the -65dBc null of the notch filter but it is low enough to not upset the spectrum analyser.
This crystal oscillator has 60dB lower phase noise (at 4.5kHz offset) compared to the E4433B sig gen!
