On Wed, 06 Apr 2022 03:30:35 -0400, time-nuts-requ...@lists.febo.com wrote: time-nuts Digest, Vol 216, Issue 10
>>> >>> Message: 4 >>> Date: Sun, 3 Apr 2022 09:53:18 -0400 >>> From: Bob kb8tq <kb...@n1k.org> >>> Subject: [time-nuts] Re: Low Phase Noise 10 MHz bench signal source >>> sought >>> To: ew <ewkeh...@aol.com>, Discussion of precise time and frequency >>> measurement <time-nuts@lists.febo.com> >>> Message-ID: <11376923-062a-4011-a6d4-1d9ce3361...@n1k.org> >>> Content-Type: text/plain; charset=utf-8 >>> >>> Hi >>> >>> These days a PLL is going to either be analog or digital. If it’s >>> analog, you get into size constraints related to capacitors >>> as you go to lower crossover frequencies. With digital, you >>> get into all of the noise issues that any digital circuit will have. >>> (Yes, they can be addressed but it’s not easy at very low >>> offset frequencies). >> >> All of the loop filters I've seen recently had nominal bandwidths in >> the Hertz >> to tens of Hertz, usually implemented in some kind of digital signal >> processor. > > 10 Hz or higher is certainly do-able with analog loop components. > There are a lot of products out there that work that way. > >> >> About 30 years ago, there was a legacy 5 MHz disciplined >> oscillator that could be set to a 100-second response time. I never >> did find any real technical data or patents on it. I don't recall >> its name, but it may come back to me. I think it was made by >> Symmetricom. I finally recalled the details, after all these years. It was from Symmetricom, they having acquired Datum in 2002. It was model FTS-1050A Disciplined Frequency Standard. Despite the implication of the product name, it does appear to be a phase-lock loop design at heart, from the users manual (my copy being dated 1999). This is the one that I suspect was in fact a 3rd-order PLL design, because it would become unstable if the the incoming reference were too faint, being far more fussy than your usual PLL, which would happily lock onto a pretty faint and ratty reference signal. It has two switch-selectable integration periods, one second and one hundred seconds. I assume that the integration is digital, but in hardware versus a computer. I can provide the documentation, if anybody wants a copy. Apparently a number of folk were looking here, over the years. Maybe something to add to Febo.com. I wonder who the designers were. Hmm. I bet that Robert Lutwak, William Riley, and Kenneth Lyon were involved, as these folk are the inventors of patents assigned to DATUM TIMING TEST AND MEASUREMENT Inc and Datum Inc in the day. I worked with Ken Lyon some time ago, if I have the right Ken Lyon. Joe Gwinn _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.