A friend and I have been messing with a DDS replacement for the VFO in older radios. The odds runs between 5 and 5.5 MHz. There are some mixers that generate the final LO frequency. We found many many birdies (caused by spurs for the non-hams) over the tuning ranges. We had to put in a lo-pass filter, 7stage commercial type to get rid of the birdies. But as I recall, there have been several cautions on this list about filters causing temperature dependence. I haven't read the whole of this thread, so it may have already been mentioned. Merry Christmas, Don
Magnus Danielson > God kväll, > > On 12/09/2015 11:47 AM, Attila Kinali wrote: >> God eftermiddag, >> >> On Tue, 8 Dec 2015 23:45:52 +0100 >> Magnus Danielson <[email protected]> wrote: >> >> >>> If you would setup essentially a micro-stepper design, such as those >>> being used for cesium and hydrogen masers, but maybe adapted to a >>> hobbyist needs and with straight-forward way of building and tune-up, >>> then we could alter the design pattern. The phase-noise and long term >>> stability issues is clear. >> >> It doesn't look too difficult to crank something out within a rainy >> weekend or two. But I am most likely underestimating the amount of work :-) > > Indeed. As any engineering time estimate, you need to multiply with pi. > At work, we engineers divide our estimates with pi before giving it to > the project managers, as they will multiply with pi before putting it > into their time-plan. :) > >>> Doing control loop using a phase-stepper is a little bit different, and >>> has a few minor design-challenges, but once mastered is essentially the >>> same. EFC or C-field control then becomes more an initial setup. >> >> What makes the control loop different (beside that you control phase >> and not frequency, and thus have to integrate)? > > Well, that is a little bit different right there. Depending on your > setup, you might have to consider how phase-wrapping and similar > saturations that happens over a long time. If you think about it, it's > manageable. > One useful trick is to let the phase-wrapping be that of the numeric > wrapping, and then handle that case for time-stamps, so that the > numerical extension becomes trivial. If you don't, you can get some very > interesting problems. > >>> An alternative approach divider wise is to use re-generative dividers. >>> For Rick's approach there would be a number of these at the same >>> frequency (nominally), so the same design-pattern would apply. However, >>> that would only be meaningful if you need really need to keep the noise >>> down. >> >> Yes, I thought about that as well, the problem here is that the low >> noise mixers designs use transformers, which make everything bulky >> and expensive (the usual suspects cost 2USD/piece and use about 1cm^2). >> The one design that comes to mind that doesn't need transformers is >> the tripple Gilbert-Cell design, but that might be higher in noise. >> (Heck, i should just sit down and do some noise calculations) >> Additionally, there is a need for relative steep filters for 667kHz > > Indeed. For most uses, re-generative dividers will not be needed. > > I should do more experiments on that stuff. > > Cheers, > Magnus > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > -- Felix qui potuit rerum cognoscere causas. Lucky is he who has been able to understand the causes of things. Virgil ------------------------------- "Noli sinere nothos te opprimere" Dr. Don Latham, AJ7LL Six Mile Systems LLC, 17850 Six Mile Road Huson, MT, 59846 mailing address: POBox 404 Frenchtown MT 59834-0404 VOX 406-626-4304 CEL 406-241-5093 Skype: buffler2 www.lightningforensics.com www.sixmilesystems.com _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
