[time-nuts] Microstepper

[Magnus Danielson]

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 <magnus at 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 at 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 at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.