Having used Brooks Shera's GPSDO since 1998 with RB's never OCXO's I still am convinced it is the best out there. The problem was the DAC which is not intended for this application. Brooks was working on a LTC1655 replacement but cancer stopped that work.We use the 16 bit LTC1655 with very good results. You ask about resolution and range. With 4 E-14 steps, range is 2.7 E-9 very acceptable for any Rb, with 1 E-14 the range is 6.75 E-10. With our FRK test results and my age of 75 I will be glad if I have the opportunity to adjust it once. We use in our work gate arrays because it is easy to correct mistakes, but before getting to know Juerg I did a Brooks 100 MHz board with discrete IC's presently still available from DigiKeys. In a message dated 7/8/2017 2:43:01 P.M. Eastern Daylight Time, listertim@gmail.com writes: On Fri, Jul 7, 2017 at 4:14 PM, jimlux <jimlux@earthlink.net> wrote: > On 7/7/17 3:14 PM, Hal Murray wrote: >> >> >> kb8tq@n1k.org said: >>> >>> Consider that in 1974, I could buy a nice new car for less than what a >>> decent packaged 16 bit DAC cost. Go back into the 1960’s and you are >>> up >>> into the “several new cars†range. Even for NASA projects cost did >>> make it >>> into the equation …. > > > Note that these papers are talking about optical ranging to the reflectors > left on the moon by the Apollo missions, but the actual work was being done > recently (e.g. it's a Microsemi 5071 Cesium clock) Right, this is the "third generation" of laser ranging. APOLLO started in 2007, so given the usual delays in obtaining grant funding and purchasing, the tech (pre-upgrade to the 5071A) is going to be early 2000s tech. Forgive the ignorance, but why is there a large disparity between ADC and DAC capabilities ? For example, Linear Technology sell a 24 bit ADC for ~$7 but an 18 bit DAC is $30-50... > >> >> When was the first GPSDO shipped as a commercial product? > > An interesting question - at least 20 years ago - XL-DC manual, Rev E, from > 1997 > http://glacier.lbl.gov/gtp/DOM/Support/xl-dc-manual.pdf > I also found it interesting that the paper says that the GPSDO uses a 2000 sec Kalman filter. I've heard of Kalman filters being used for GPS navigation but not in timing use, although I gather things like Thunderbolts use a ~1000 sec loop constant - is this the same form of filtering or have different forms of filtering become more popular and Kalman filtering is no longer used ? > >> >> There is an interesting tradeoff in GPSDO design. With a specific DAC, >> you >> can get finer steps if you reduce the tuning range. Has anybody built one >> with a reduced range and a knob on the side to adjust the center point of >> that range? You would have to adjust that knob occasionally as the >> crystal >> you are tuning drifted. > > > My mid 2000s 10 MHz OCXOs from Wenzel have both EFC and a manual adjustment > of some sort (I'm not sure what's under the little cap on the side.. a > trimmer cap or something?) > Right. Apparently the DAC values have changed by 3500 over the ~11 years, which given the 1.2e-11 DAC steps would give an accumulated change of 4.2e-8, agreeing with the typical and quoted ~1e-11/day drift/aging for a good OCXO. Tim _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.