[time-nuts] WWVB teensy BPSK early experiments

[paul swed]

Good suggestions. The Teensy runs at some 580 MHz. I thought on the crystal
I had seen something like 166. These things are seriously small. But the
schematic shows its 24 MHz.
Inside the teensy is a PLL that creates the high speed system clock. So
thats potentially a good answer. Use something like either a 20 or 25 Mhz
vcTCXO as John did in the KD2BD receiver. It will be seriously tough
getting the micro 4 pin crystal out without damaging the board.
Secondary effect will occur by changing the xtal. Such as audio sample
rates. Not sure there are real world effects to really consider.
Time to pull the microscope and see.
Regards
Paul


On Sat, Oct 31, 2020 at 5:55 PM John Ackermann N8UR <jra at febo.com> wrote:

> Just a thought, Paul --
>
> If the teensy can generate an output that is accurate but jittery, you
> could use a simple PLL to lock a crystal to that with a time constant
> that smooths out the jitter.
>
> John
> ----
> On 10/31/20 1:47 PM, paul swed wrote:
> > Hello to the group. Wanted to update the everyone thats interested in
> > what I have learned so far on the Teensy and audio codec. No complete
> > solution yet. Much of my experimentation and knowledge has come from
> Frank
> > and Chris, who built the complete wwvb AM time receiver. In addition
> > and important is Johns KD2DB BPSK receiver. There is a reason this
> matters.
> >
> > The teensy combination is powerful and somewhat easy to use. (Has to be
> for
> > me). So over the week or so it's been getting used to the audio libraries
> > and how pieces are connected in software and then seeing the results. All
> > of the base experiments worked very quickly. Simple things like signal
> > generators, multipliers and filters. Things already accomplished by Chris
> > in the wwvb AM receiver.
> >
> > But the question really is what to accomplish?
> > If its the wwvb bpsk timecode. Simply buy an ES100 and be done.
> >
> > The interest that I have is a locked reference. Minimizing soldering and
> > construction. This is the point things get interesting.
> > A NCO can be created in Teensy but it tends to be low frequency and a
> > multiple of 60 KHz. Stability sort of isn't. But if it could be created
> > then a complete frequency reference in the teensy could be accomplished.
> > That makes for a heck of a low power receiver 1 watt, inexpensive, and
> > little soldering.
> > The above path literally follows the old Spectracoms and Truetime direct
> > conversion receivers.
> > Have to look at their schematics because they do lock a useful reference.
> > But that means something external has to come into the teensy. Get the
> > soldering iron hot.
> >
> > The other approach is essentially Johns KD2BD receiver in software with
> an
> > external reference chain delivering 50KHz and 10 KHz to the teensy. Well
> > this is getting ugly now because that external chain is made up of a
> > classical divider 10 MHz to 50 KHz etc. But does give a very nicely
> locked
> > useful wwvb reference. Its really a hybrid because it significantly
> reduces
> > the soldering required in a true KD2BD receiver but isn't the pure in
> > a chip solution.
> >
> > All of this is just for fun because the fact is the GPDSOs we use are
> > better.
> > If a receiver is built a natural by-product is the time message. Its just
> > not my focus or interest.
> > Much more to learn.
> >
> > Next steps
> > Start to reuse the wwvb teensy AM receiver.
> > Chop out all of the display software. Its all very nice but for me at
> this
> > stage gets in the way of understanding things.
> >
> > With respect to I&Q generation several suggestions have been made. But
> the
> > teensy supports multiple multipliers. Sort of thinking, use the sine
> > wave oscillator and add a 90 degree delay to a second path to a second
> > multiplier. An alternative inject the delay in the wwvb signal also. How
> > fine a delay is a serious question.
> > Much to learn and potholes to fall into.
> > Regards
> > Paul
> > WB8TSL
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