[time-nuts] WWVB teensy BPSK early experiments

[paul swed]

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