[time-nuts] WWVB teensy BPSK early experiments

Sun Nov 1 17:48:26 UTC 2020

John sent the link on the teensy wwvb AM receiver. It can easily be shifted
to other frequencies. Using the work Frank dcf77 and then Chris wwvb did
with the PJRC audio design tool gives quite a bit of insight to the work
that was done.
The system assumes a sample rate of 192Khz. That limits the receive range
to about 98KHz.
I have not been able to confirm the rate I am using is 192Khz and when the
set command is used its not recognized. So somethings up.
The design Chris has essentially is a microphone input with some 38 db of
gain feeding a bandpass filter around 60 KHz to a multiplier (RF mixer)
then a low pass filter. Chris and Franks design is much more than these few
words with spectrum display, signal level, and AGC.
So without any effort the frontend solution is sitting in the teensy that
cuts out a bunch of typical wiring. Granted its not as tight as discrete
components can be. But its a chunk of software code. No digi key orders for
L & Cs... :-)
The output of the chain is 600 Hz audio that does contain the phase changes.

But the trick is creating the true I & Q channels. Not an issue to add a
second multiplier and chain did that last night. But at someplace a 90
degree phase change or delay needs to occur.
Or as suggested a hilbert transform.
Regards
Paul
WB8TSL

On Sun, Nov 1, 2020 at 5:35 AM <rcbuck at atcelectronics.com> wrote:

> Thanks John.
>
> Ray,
> AB7HE
>
> -------- Original Message --------
> Subject: Re: [time-nuts] WWVB teensy BPSK early experiments
> From: "John C. Westmoreland, P.E." <john at westmorelandengineering.com>
> Date: Sat, October 31, 2020 9:06 pm
> To: Discussion of precise time and frequency measurement
> <time-nuts at lists.febo.com>
>
> Ray,
>
> https://github.com/chris-elfpen/Teensy4WWVBsdr
>
> 73's,
> John
> AJ6BC
>
>
> On Sat, Oct 31, 2020, 18:31 <rcbuck at atcelectronics.com> wrote:
>
> > Bob,
> >
> > "Things already accomplished by Chris in the wwvb AM receiver"
> >
> > Is there a link to the AM receiver? Curious as to what that looks like.
> >
> > Ray,
> > AB7HE
> >
> > -------- Original Message --------
> > Subject: Re: [time-nuts] WWVB teensy BPSK early experiments
> > From: Bob kb8tq <kb8tq at n1k.org>
> > Date: Sat, October 31, 2020 11:42 am
> > To: Discussion of precise time and frequency measurement
> > <time-nuts at lists.febo.com>
> >
> > Hi
> >
> > …..errr…..
> >
> > Can you pull the clock oscillator off the Teensy board? (Yes, the
> > soldering
> > iron would be involved).
> >
> > Will the clock input to the MCU accept something like 10 MHz? If so
> > solder
> > on a cable ….
> >
> > At that point whatever the Teeny does is locked to the 10 MHz. If that
> > comes
> > from one of the $3 eBay OCXO’s, steer that with a DAC output … now
> > you
> > have a WWVB GPSDO.
> >
> > Indeed, if the Teensy needs 28 MHz, then the OCXO will not be quite as
> > cheap.
> >
> > Bob
> >
> > > On Oct 31, 2020, at 1:47 PM, paul swed <paulswedb at gmail.com> 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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