[time-nuts] WWVB Dephaser Question

[paul swed]

Thanks everyone for the responses. Enough for now. Time to make anything
happen.
Will let you know and perhaps start a new thread around this.
Regards
Paul
WB8TSL

On Sat, Oct 24, 2020 at 10:17 PM Graham / KE9H <ke9h.graham at gmail.com>
wrote:

> Paul:
>
> The easiest way to convert a single sample into an I-Q representation is to
> have a two phase local oscillator.
> You multiply the incoming signal against the primary phase output of the
> oscillator for the I channel,
> and multiply the same sample against the 90 degree offset output for the Q
> channel.
>
> The quadrature oscillator can be as simple as two sine look-up tables,
> whose entries are shifted by 90 degrees.
> The only math is in the sample multiply, and creating the look up tables to
> start with.
>
> If there is a ratio of integers relationship between the sampling rate and
> the desired local oscillator frequency, then you can get a real clean
> implementation with reasonably small look-up tables.  When running there is
> no transcendental math involved, just a simple multiply.
>
> --- Graham
>
> ==
>
> On Sat, Oct 24, 2020 at 7:37 PM paul swed <paulswedb at gmail.com> wrote:
>
> > Antenna and filtering are not a problem for me. I use the 10' X 10'
> square
> > loop and about 800' of wire with a cap to resonate at 60 KHz and then a
> > preamp really to drive 140' of coax. Currently using a modified KD2BD
> > receiver frontend but using a 350 Hz xtal filter. Yes indeed that hamfest
> > find was amazing.
> >
> > Looks like you have to build a costa loop SDR. Looked at lots of
> documents.
> > My first question to the group.
> > Can a single incoming sample be converted to I & Q through math. I sort
> of
> > think so. The original sample might be I and then use math to make Q.
> That
> > would save an entire analog chain. The teensy has a single chain for mic
> > level input. Though it does feed left and right channels. Granted there
> are
> > two audio chains at line level.
> >
> > The teensy has a NCO that can create a quadrature output. The alternate
> > would be to use that to drive analog switches as a multiplier to form I
> & Q
> > samples.
> > Regards
> > Paul
> > WB8TSL
> >
> >
> >
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