[time-nuts] WWVB d-psk-r down conversion method

[paul swed]

Bob
You missed nothing really. 100 Hz because thats what the NAA radio used
with the tracor doubler. So when I moved it to wwvb that was the baseband
signal.
Now that said I liked the 1 second phase flips at 100 Hz delay. Dog slow
and perfectly OK to resolve the phase flip and I can use my favored uproc.

Whats funny is that any crystal close to anything existed.
Digikey says they have a 6.1Mhz xtal but when selected goes to 6.144 MHz.
I was amazed that both mouser and digikey had the 5.9904 xtals and both
stocked a variety of cases. Must be some story about whatever that
frequency is.
Did try lots of frequencies and divider math to come up with a simple LO
scheme for 61 or 59 KHz. Messy.
Regards
Paul
WB8TSL


On Mon, Sep 22, 2014 at 7:42 PM, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
> Is it really that much harder to process a 1 KHz note out of a direct
> conversion receiver than it is to process a 100 Hz note?
>
> Put another way - you already have a crystal filter in the front end of
> the “radio” right? It will do a better job knocking down an “adjacent
> channel” 2 KHz away than one 200 Hz away. Even without the crystal filter,
> the only likely thing you are trying to reject is noise. Effectively the
> “no filter” approach degrades your signal to noise by 3 to 6 db depending
> on the type of noise you are dealing with.
>
> I’m asking because I may have missed something that makes 100 Hz “magic” ….
>
> Bob
>
> On Sep 22, 2014, at 6:15 PM, paul swed <paulswedb at gmail.com> wrote:
>
> > One of the methods suggested for working with the wwvb psk is down
> > converting to a lower frequency. When experimenting with NAA I had built
> a
> > 24 Khz receiver that down converted that signal to a 100 Hz base band.
> > It was a minor effort to shift it to 60 Khz by changing the LO. I liked
> > what I saw. Essentially a simple direct conversion receiver with about 42
> > DB of gain.
> > The PSK flips at every 1 second depending on the data and is 1/100Hz
> > delayed from the wwvb flip due to the down conversion process. This makes
> > the further processing very reasonable in just about any micro.
> > But the LO is a mess. Not bad if you have an HP3335a as I did till last
> > week. (Another project to repair) for 100 Hz the LO must be at 60.1 or
> 59.9
> > Khz. Or synthesize it etc. Starting to get seriously ugly.
> > Or jump to a 1 Khz with 59 or 61 KHz. But I hated the idea of mixers and
> > filters.
> >
> > Any Time-Nuts seen those crystals or oscillators around lately? Seriously
> > missing from the general haunts.
> >
> > But turns out and heavens knows why there are plentiful 5.9904 MHz xtals
> > around. I ordered 5 from Mouser $ .46 ea.
> > 5.9904/100 = 59.904 as a LO and suspect it can be moved to the correct
> > frequency not that it has to be.
> > Not sure there is a real need to lock the LO at all.
> > So an exciting bit of news.
> > Regards
> > Paul
> > WB8TSL
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