[time-nuts] WWVB Dephaser Question

Mon Oct 12 14:40:47 UTC 2020

John really appreciate the pointer. Though it doesn't help wwvb BPSK its a
really good intro to SDR and DSP super simple. A good way to get your feet
wet. Hmmm is there a parts order soon? :-)
Regards
Paul
WB8TSL

On Mon, Oct 12, 2020 at 10:33 AM Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> The “ideal” antenna solenoid would be a bit longer ( say 2 X to 5X ).
> The turns should be spaced apart by a few percent of the length.
> ( so turns over 30 or so … not so much …).
>
> How much better is “ideal” compared to “just get it done?”.  At least
> from the stories that are told, it is significant. Since all these antennas
> are very small (so non-ideal) it’s a bit of a snail race.
>
> Bob
>
> > On Oct 12, 2020, at 3:42 AM, John C. Westmoreland, P.E. <
> john at westmorelandengineering.com> wrote:
> >
> > Paul,
> >
> > Doesn't the post by Chris Howard above appear to be a good/great starting
> > point?
> > Seems like that approach could be extended.
> >
> > https://github.com/chris-elfpen/Teensy4WWVBsdr
> >
> > 73's,
> > John
> > AJ6BC
> >
> >
> > On Sun, Oct 11, 2020 at 9:23 AM paul swed <paulswedb at gmail.com> wrote:
> >
> >> Good morning to the group. Both Rodger and I can answer the last
> question
> >> on the questionable bits very well.
> >> I have 7 antique devices spectracoms truetime fluke tracor Dymec etc.
> >> They handle it very well each has at least a 2 second integration time.
> The
> >> dpskr has always taken advantage of this fact. Literally we have run
> days
> >> without flips in the charts. Even in summer.
> >> Some surprises in doing this. Numbers of bits that could change don't
> seem
> >> to. Then some of the bits have a really odd pattern but they follow the
> >> pattern. Thats been coded into the dpskr. In fact anything over several
> >> years we have figured out are coded in.
> >> One thing we did not do was automatic change from summer to winter
> offsets.
> >> Its really a PIA so just not that excited when this happy switch flipper
> >> can do it in 1 second.
> >>
> >> The other bit of fun for the magical new DPS wwvb receiver is after you
> get
> >> the bits you must decode them and its nothing like the AM code. Its a
> M/N
> >> FEC code. Its all in the NIST papers but was fun coding and I imagine
> every
> >> bit as fun decoding. The dpskr software at least gives you hints to the
> >> process.
> >>
> >> Here is an offer. Anyone that gets the BPSK bits working through a
> SDR/DPS
> >> arduino/STM cheap chip. Please no $100 FPGA development kits.
> >> I will be happy to dig into the decoder. The solution needs a 1pps and
> the
> >> bit.
> >> Whats really funny about the wwvb bpsk is that there has never been
> sort of
> >> a open development platform. Anyone who has played with the ES100 will
> run
> >> into some issues that are annoying for a time nut to tinker with.
> >> Regards
> >> Paul
> >>
> >> On Sun, Oct 11, 2020 at 10:39 AM Bob kb8tq <kb8tq at n1k.org> wrote:
> >>
> >>> Hi
> >>>
> >>> The “simple” approach is to generate the full modulation pattern
> >>> for the signal based on a “known good” time source. There are a
> >>> couple of ambiguous  bits so it will only be close. Feed that into
> >>> your inverter and the result will be (near) clean WWVB. Since you
> >>> never demodulate the WWVB, there isn’t a lot to the RF side ….
> >>>
> >>> There will be some drops and pops. The question will be just how
> >>> well this or that antique device deals with them.
> >>>
> >>> Bob
> >>>
> >>>> On Oct 10, 2020, at 10:01 PM, paul swed <paulswedb at gmail.com> wrote:
> >>>>
> >>>> The additional article John sent us is a pretty good read. Having
> >>> soldered
> >>>> all the little wires together with heat shrink, I can see the
> advantage
> >>> of
> >>>> the epoxy approach.
> >>>>
> >>>> A consideration for the discussion. So far its been about the various
> >>> tried
> >>>> and true methods for a RF frontend. But the real challenge that is in
> >>> front
> >>>> of us is the software that uses that frontend. How about a very easy
> to
> >>>> build a phase flipper so that those that are software inclined do not
> >>> need
> >>>> to deal with the frontend to get going. The dpskr has a phase flipper
> >> in
> >>> it.
> >>>> But it can be even simpler than that.
> >>>>
> >>>> A 60 KHz logic signal ( divide 6 Mhz down or anything else thats easy)
> >>>> Feeds an inverter to generate the 180 degree phase. A gate to select 0
> >> or
> >>>> 180 degrees. All of the gates/inverters can actually be a single quad
> >>>> nand gate. A D flip flop with the clock from the 0 degree 60 KHz logic
> >>>> level. Your data into the D input. The D flip flop synchronizes the
> >> data
> >>> to
> >>>> the clock. On the output you can filter the signal or not and cut the
> >>> level
> >>>> down or not.
> >>>> Its a BPSK source.
> >>>> Granted in a pure gate approach the actual bpsk flip will not be the 2
> >> X
> >>> 60
> >>>> KHz for 1/2 cycle. But in real receivers the 120 KHz never comes
> >> through
> >>>> the various stages and filters. So no real harm. This also doesn't
> >> supply
> >>>> the AM signals 14-17 db modulation. But its good enough to allow
> >> software
> >>>> to be developed and its simple.
> >>>> Good luck
> >>>> Paul
> >>>> WB8TSL
> >>>>
> >>>> On Sat, Oct 10, 2020 at 2:05 PM John Magliacane via time-nuts <
> >>>> time-nuts at lists.febo.com> wrote:
> >>>>
> >>>>> For WWVB reception, I use a single turn of 40-conductor ribbon cable,
> >>>>> configured as a 40-turn loop, brought to resonance with a parallel
> >>>>> capacitance, that differentially drives an instrumentation amplifier.
> >> No
> >>>>> electrostatic shielding is needed to eliminate e-field pickup with
> >> this
> >>>>> approach.
> >>>>>
> >>>>> The antenna hangs in my attic with thumbtacks and does a commendable
> >>> job,
> >>>>> day or night, 1622 miles east of WWVB.  See attached JPEG image.
> >>>>>
> >>>>> The March 2017 issue of "Circuit Cellar" magazine described an
> >>> "improved"
> >>>>> version of my antenna/preamp combination (which I haven't looked
> >> into).
> >>>>> See attached PDF document.
> >>>>>
> >>>>> During my early experimentation, I realized that the preamp would
> need
> >>> to
> >>>>> have a high dynamic range in order to perform well in the high-noise
> >>>>> environment that is LF.   And if the preamp is going to feed a
> >> receiver
> >>>>> through any reasonable length of coax, it will need to be able to
> >> drive
> >>> a
> >>>>> high capacitance load as well.
> >>>>>
> >>>>>
> >>>>> 73.000 de John, KD2BD
> >>>>> _______________________________________________
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