Yet another interesting time nuts conversation. A few comments: 1 A number of comments stated as a "fact" that higher unloaded Q for the resonator corresponds to lower phase noise. This idea evidentially comes from looking at analysis of a so-called free running oscillator with a simple LC tank or microwave resonator, as published by Edson, Kurakawa, and Cutler/Leeson. However, even in this case, what matters is the LOADED Q, and the drive level to the sustaining amplifier. A given drive level will have a particular phase noise and flicker noise floor associated with it. Incidentally, the resonator should be critically coupled, in which case Ql = 1/2 Qu, for optimum phase noise., 2. With a piezo electric resonator, the intrinsic flicker noise of the resonator dominates, and it isn't related to Q (unloaded to loaded). The sustaining amplifier ordinarily is not a factor. 3. I personally measured the intrinsic phase noise of a free-standing 10811 crystal and compared it to the phase noise of a 10811 oscillator with that same crystal installed. The conclusion was that the oscillator phase noise was basically the same as the intrinsic crystal noise, except at large frequency offsets. 4. The only possible scenario I can see for why an SC cut might have better phase noise is if you don't have a very good oven. Then ADEV at long averaging times starts to go up. In that case, an SC cut might help because of improving tempco. 5. Phase noise at large offsets (>1kHz) depends on the buffer amplifier design. The grounded base design in the 10811 is the optimum first stage. Unfortunately, the 2nd and 3rd stages in the 10811 degrade its phase noise. This has little or nothing to do with the cut of the crystal or anything else about it. (The idea for this was published by U. Rhode and later patented by Burgoon of HP). 6. The primary motivation for the SC cut at the HP Santa Clara division (where I worked) was to be able to put it into a frequency counter used for field maintenance. The idea was that the technician could carry it from his truck into the worksite and plug it, starting from a cold oven. Then, in only 15 minutes, the counter met some accuracy spec. With a 10544, it would take many times longer to get to the same accuracy. Jack Kusters used to say that "SC" actually stood for "Santa Clara" :-) Rick N6RK _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Is SC the most stable cut for lowest phase noise?
Richard (Rick) Karlquist via time-nuts Thu, 09 Jun 2022 12:53:19 -0700
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