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This agrees with the various snippets of design information I've found across the years from various sources (G3VA's "Technical Topics" in particular). That is - the coupling capacitors should be reduced to the smallest value consistent with reliable starting. I'm fairly sure that too much coupling was reported to degrade stability, and possibly other issues (spurious oscillations, noise ?).
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In theory at least, the loaded Q should keep going up as the coupling caps are reduced. A doubling in loaded Q should improve the phase noise by about 6dB. However, once the ratio between unloaded and loaded Q starts to tumble, the insertion loss in the resonator will become significant and it will affect the phase noise result. So there comes a point when it doesn't bring much benefit in phase noise. Leeson's equation doesn't have an entry for resonator loss and I usually degrade the noise figure of the active device by the loss in the resonator (in dB) to cater for this.
The other way to do it is to measure the resonator power the conventional way and then enter a lower figure for the power into the spreadsheet that allows for resonator losses.
I think the little MMIC trainer only shifts about 20Hz (at 10.7MHz) between an initial noise peak of -50dBm and something that looks like a regular oscillation signal at 0dBm as the loop attenuation is reduced. The regular output is about 11 or 12dBm although it can go up to +16dBm with a bit more MMIC bias and no attenuation in the feedback. However, I'm not changing the loaded Q when I do this. I do recall playing with the resonator tap points when sat in front of the E5052A analyser at work and there wasn't much change in phase noise because I think my resonator has 2 or 3dB loss and I ended up trading insertion loss against loaded Q with little benefit. But I didn't do this in a very controlled manner.