[time-nuts] WWVB Dephaser Question

[jimlux]

On 10/24/20 3:53 PM, paul swed 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

The classic way to get I/Q is to sample at 4 times the desired rate, 
then, given that your input samples are x(1),x(2),x(3),x(4), etc. the 
I/Q streams are

I(1) = X(1)
Q(1) = X(2)
I(2) = -X(3)
Q(2) = -X(4)
I(3) = X(5)
Q(3) = X(6)
I(4) = -X(7)
Q(4) = -X(8)

and so forth.

This will put your signal right in the middle of the sampling bandwidth.