Jim Lux wrote:
Actually, all H-Maser I know rely on a really high quality xtal for their short-term stability (and hence intrinsic phase noise); by high quality, I mean BVA xtal units costing in the $5k range. The transition from the BVA xtal to the maser is typically done at times ~30-100 seconds or so (see the AVARs in my tutorials I mention later, or http://www.leapsecond.com/museum/manyadev.gif to see that the BVA performance is better than the Maser up to ~30 seconds. The goal is to "hand off " from one oscillator to the next when their Allen deviation is equal).There ARE actually sources with better close in phase noise than a quartz crystal, just in case you see one at a hamfest or surplus place (or, you're wealthy enough). A hydrogen maser, for instance (that's what we use at work, JPL, when we're concerned about such things.. but then we have an infrastructure to distribute the maser signal around, and a budget for the support staff). BTW -- we actually have a couple of "amateurs" that have both passive & active H-Masers in their basements. One is Tom vanBaak (no call) whose efforts can be viewed at http://leapsecond.com/ and another is Jim Jaeger (K8RQ) (see http://www.clockvault.com/ if you can stand the music!). TvB offered a review paper on amateur timekeeping at the 2003 PTTI meeting, which can be fetched at http://tycho.usno.navy.mil/ptti/ptti2003/paper35.pdf. Also be sure to note TvB's "Most Accurate WristWatch" when you log onto leapsecond.com. I've said it before, and I'll repeat it now -- you are better off thinking in the frequency (and phase noise) domain when you are considering oscillators on time scales shorter than tens of seconds, and in the time domain for minutes and longer. If you are interested in these topics, you might want to fetch one of my "Timing for VLBI" tutorials at http://gpstime.com/ . In my past incarnation I ran NASA's Geodetic VLBI program and was responsible for H-masers as time and frequency standards. While I am on here making comments on this thread, I note that Alberto, I2PHD is using a circuit similar to the one I developed for locking an xtal to the 10 kHz output from the Connexant/Navman Jupiter-T receiver. A couple of notes on what I found:
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- Re: [Flexradio] Frequency stability and calibration Tom Clark, W3IWI
- [Flexradio] Frequency stability and calibration john_eckert
- Re: [Flexradio] Frequency stability and calibrati... John Ackermann N8UR
- Re: [Flexradio] Frequency stability and calibrati... Jim Lux
- Re: [Flexradio] Frequency stability and calib... Tom Clark, W3IWI
- Re: [Flexradio] Frequency stability and calibration john_eckert