Am 2022-06-08 21:53, schrieb Tom Van Baak: > Would it be advantageous, then, to run a high-performance laboratory > oscillator at its lower turnover point? Or at -78 C (CO2) or 77 K > (liquid Nitrogen)? I have no idea about the crystal itself. Maybe Bernd or the SC (SantaClara) veterans can help? When I measured the Q of the recovered SC crystal from that Morion MV89A, there was not much of a difference in the wanted resonance between room temperature and +89°C. I think I have published the data here a year ago. My deep freezer in the basement can do -36°C, but the VNA is so heavy... Infineon boasted that their SIGET transistors work nicely at a few Kelvin, so it would probably not fail for semiconductor availability (BFP640 & friends). OTOH, Ulrich Rohde wrote that the noise figure of the sustaining amplifier would take a hit under large signal conditions, but I don't know hard numbers. That would not disappear. But then, in a Driscoll for example, you can give the 2 transistors enough current so they run class A and do the little bit of limiting on the output side with Schottkys. For the amplifier, that is not large signal. That might be different for an amplifier in Lee-Hajimiri style. This is Dirac pulse excitation at the peak of the cycle to avoid phase modulation, that is optimized for mixing up 1/f noise. :-) Anyway, with a noise figure of the sustaining amplifier of a dB or even a few, there is no game changer to be expected from cooling. Whispering gallery saphire, anyone? I was at the precious stones museum in Idar-Oberstein here in the 'hood and saw all these huge saphires. I left with the head full of ideas... Cheers, Gerhard

Hi Lower turning point has been done, both with AT’s (back in ~ the 1950’s) and with SC’s. Neither one showed any significant benefit. Taking a crystal down to sub 20K sort of temps does ramp up the Q. The gotcha is that the frequency vs temp curve is so steep that very minor temperature variations utterly trash the stability of the device. Bob > On Jun 8, 2022, at 1:49 PM, Gerhard Hoffmann via time-nuts <time-nuts@lists.febo.com> wrote: > > Am 2022-06-08 21:53, schrieb Tom Van Baak: >> Would it be advantageous, then, to run a high-performance laboratory >> oscillator at its lower turnover point? Or at -78 C (CO2) or 77 K >> (liquid Nitrogen)? > > I have no idea about the crystal itself. Maybe Bernd or the SC (SantaClara) > veterans can help? > > When I measured the Q of the recovered SC crystal from that Morion MV89A, > there was not much of a difference in the wanted resonance between room > temperature and +89°C. I think I have published the data here a year ago. > My deep freezer in the basement can do -36°C, but the VNA is so heavy... > > Infineon boasted that their SIGET transistors work nicely at a few Kelvin, > so it would probably not fail for semiconductor availability (BFP640 & friends). > OTOH, Ulrich Rohde wrote that the noise figure of the sustaining amplifier would > take a hit under large signal conditions, but I don't know hard numbers. > That would not disappear. > > But then, in a Driscoll for example, you can give the 2 transistors enough > current so they run class A and do the little bit of limiting on the output side > with Schottkys. For the amplifier, that is not large signal. > > That might be different for an amplifier in Lee-Hajimiri style. > This is Dirac pulse excitation at the peak of the cycle to avoid phase modulation, > that is optimized for mixing up 1/f noise. :-) > > Anyway, with a noise figure of the sustaining amplifier of a dB or even a few, > there is no game changer to be expected from cooling. > > Whispering gallery saphire, anyone? I was at the precious stones museum > in Idar-Oberstein here in the 'hood and saw all these huge saphires. > I left with the head full of ideas... > > Cheers, Gerhard > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

Hi, The ability to stabilize at that temperature is indeed an issue. While the resonators Q shift, the loaded Q I would not expect to shift as much. Futher, the noise of the supporting amplifier also needs to be reduced. Naturally, the design could be adjusted to the different condition. I've seen people taking "the best" oscillator (SC-cut) and go cryogenic, and then have severe temperature issues, because they did not understand that the benefit of the cut really manifest itself at some specific temperature. Luckily that they was able to get that feedback as the benefit of presenting to their peers at a conference. Cryogenic provides an oppertunity, but as with any such condition, it takes a number of considerations to be able to harvest the benefits. Cheers, Magnus On 2022-06-09 02:12, Bob kb8tq via time-nuts wrote: > Hi > > Lower turning point has been done, both with AT’s (back in ~ the 1950’s) and > with SC’s. Neither one showed any significant benefit. > > Taking a crystal down to sub 20K sort of temps does ramp up the Q. The gotcha > is that the frequency vs temp curve is so steep that very minor temperature variations > utterly trash the stability of the device. > > Bob > >> On Jun 8, 2022, at 1:49 PM, Gerhard Hoffmann via time-nuts <time-nuts@lists.febo.com> wrote: >> >> Am 2022-06-08 21:53, schrieb Tom Van Baak: >>> Would it be advantageous, then, to run a high-performance laboratory >>> oscillator at its lower turnover point? Or at -78 C (CO2) or 77 K >>> (liquid Nitrogen)? >> I have no idea about the crystal itself. Maybe Bernd or the SC (SantaClara) >> veterans can help? >> >> When I measured the Q of the recovered SC crystal from that Morion MV89A, >> there was not much of a difference in the wanted resonance between room >> temperature and +89°C. I think I have published the data here a year ago. >> My deep freezer in the basement can do -36°C, but the VNA is so heavy... >> >> Infineon boasted that their SIGET transistors work nicely at a few Kelvin, >> so it would probably not fail for semiconductor availability (BFP640 & friends). >> OTOH, Ulrich Rohde wrote that the noise figure of the sustaining amplifier would >> take a hit under large signal conditions, but I don't know hard numbers. >> That would not disappear. >> >> But then, in a Driscoll for example, you can give the 2 transistors enough >> current so they run class A and do the little bit of limiting on the output side >> with Schottkys. For the amplifier, that is not large signal. >> >> That might be different for an amplifier in Lee-Hajimiri style. >> This is Dirac pulse excitation at the peak of the cycle to avoid phase modulation, >> that is optimized for mixing up 1/f noise. :-) >> >> Anyway, with a noise figure of the sustaining amplifier of a dB or even a few, >> there is no game changer to be expected from cooling. >> >> Whispering gallery saphire, anyone? I was at the precious stones museum >> in Idar-Oberstein here in the 'hood and saw all these huge saphires. >> I left with the head full of ideas... >> >> Cheers, Gerhard >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-leave@lists.febo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

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