Dana, What motor? I have no motor involved here.
Alternating between frequencies causes modulation I try to avoid, a DDS is a good way to avoid that, but I was hoping to keep phase noise low. Cheers, Magnus On 2019-12-25 03:03, Dana Whitlow wrote: > Magnus, > > Why not just clock a good DDS (AD9854) with the reference frequency, and > run its > I & Q outputs into the motor via suitable LP filters and some power gain? > You might > need to periodically alternate between two different output frequencies to > get the desired > rotation speed (as with a fractional N divider), but with the 48-bit DDS > I'd think that this > would work well. After all, the magnetics in a motor are not all that > accurate anyway- > one cannot get perfection in avoiding salient pole effects etc. > > Dana > > > On Tue, Dec 24, 2019 at 6:02 PM Magnus Danielson <mag...@rubidium.se> wrote: > >> Hi, >> >> I realize that I lack a microstepper. Consider that I have a stable and >> low-noise 5 or 10 MHz but I want to resynthesize to correct frequency >> and do phase-steps, and doing so without too much loss of noise. >> >> This has traditionally been done using a variation of techniques, but if >> we would use some of the things that happened lately, pretty OK >> performance should be possible to achieve without too much hardware. >> >> OK, so after a discussion with Bob, here is one sketch for a >> possibility, just to toss one proposal to crush into pieces and propose >> improvements or better versions. >> >> So, consider using a modern Silabs chip clocked from an oscillator, >> producing a offset generator with I/Q and then do an I/Q mixdown to a >> beat frequency, which is digitized by a pair of ADCs. A pair of DACs >> produces I/Q which is used to mixed to produce the output signal using >> the signals from the Silab. The ADCs/DACs can be either be fed to some >> CPU platform or FPGA. With this platform one can choose to servo the >> reference oscillator, or just modify the beat received. Maybe use a >> Raspberry Pi as platform. Rotating the vector and steering the rate of >> rotation should not be extremely hard to do. The input vector can be >> added internally or used to steer the oscillator. Either way, the in >> loop noise from the Silabs will be fairly well suppressed since it only >> acts as a transfer oscillator. >> >> So, suggestions, thoughts and improvements? >> >> God Jul and Merry Christmas! >> >> Cheers, >> Magnus >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.