Quote:
Originally Posted by G0HZU_JMR
But if I keep reducing the attenuation, the oscillator frequency then starts to shift sideways as the active device gets driven harder and harder into a non linear state. Leeson's equation begins to fail here too because I think the large signal noise figure of the MMIC degrades when driven too hard like this. The frequency stability is worse when in this state and this is only with about 6-7dB excess gain in the loop.
|
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 ?).
None of this puts me off, as I'm not in the business of building a state of the art signal source. Rather, the exercise might be compared with - for example - building a regenerative receiver using modern components. Basically - to see how well it works, and how comparable it can be to the conventional approach.
Curiousity, and perhaps a bit of eccentricity is the driver, I think.