Clint Nice writeup but will say its to late to effectively reply perhaps tomorrow. So early on I did all sorts of oscillators and such looking for the magical carry through. They just didn't work. The other thing is that I can do a lot of things just for myself with parts no one else can get and thats not been the goal. I want to be able to say get a digikey this or a mouser that. I never plan to build kits. Bless those time-nuts that do make that effort. It really is a job. So I like to build what I hope are reproducible things.
You mention using things like CD4000 series. I am not proud and if that works fire up the iron I have plenty of the 4000 series. But as I mention I have been introduced to the STM eval board and it can run Forth and it moves along well with 12 bit A>Ds and D>As. Multiples of them. Its just crazy the technology we have for $15 today. Regards Paul. On Fri, Feb 21, 2014 at 9:55 PM, Clint Turner <tur...@ussc.com> wrote: > Hi Paul, > > Without digging through the archives, I'll rely on your memory of that > past thread! > > The scheme of using the doubler relied on the 100 kHz carrier recovery > relied on the fact that the 200 kHz bandpass filters, being based on quartz > crystals, was extremely narrow - on the order of fractions of Hz. This > effectively made them frequency-selective integrators (not the right word, > but you get the idea...) and they were effectively immune to noise pulses > as they simply could not react quickly. > > IIRC - and I'll have to review my old notes - I used the first 200 kHz > crystal as a series element and then passed it to a source-follower and > then a bipolar amplifier with ridiculous gain (e.g. grounded emitter, high > collector resistance) to form a limiter - and then ran it through another > 200 kHz crystal and JFET/limiter. It took a couple of seconds for the > outputs of the two limiters to saturate due to the narrow bandwidth and it > was extremely tolerant of amplitude variations. There was a phase shift > with different amplitude levels, but since, on an FM microwave link the > amplitude wasn't going to change much, that - and the phase shift related > to temperature - was inconsequential. > > On this simple recover scheme you could remove the input carrier for > nearly a second (or blot it out with noise) and there would be almost no > measurable effect on the output, aside from a phase shift of a few 10's of > degrees which quickly rectified itself once the signal was returned. Had > added some better tuning of the resonators I could have likely minimized > this. (I happened to have these 200 kHz HC-6 style units in my semi-large > collection of 40-80's vintage crystals.) > > The trick to replicating such a filter would be to find a suitable > bandpass filter for the doubled frequency - in this case, a 120.005 kHz > crystal (or thereabouts) - but it should be practical to convert the > previously-filtered 60 kHz signal to a frequency for which a suitable > crystal could be located. > > The 60.003 kHz crystal to which I referred was a bandpass filter rather > than an oscillator: The TRF units found in WWVB clocks use these since > most standard 60.000 kHz units end up being low in frequency when used in > this sort of mode and they are a bit tricky to "pull" this far. > > Rather than try to find such a crystal I would probably throw together a > "Tayloe" commutating mixer with RC lowpass filtering with a time constant > of a hundred milliseconds or so - this, filter/mixer being clocked at the > nominal 60 kHz receive signal. > > I would then follow it with another commutating mixer to translate the > quadrature signal to any convenient frequency (say, audio - no doubt > available from the 4060 or 4040 counter I'd be using!) where I would then > do my frequency doubling and then follow it by yet another extremely narrow > filter - this time, using an 8-capacitor SCF where I could set the > detection bandwidth to a tiny fraction of 1 Hz just using a bunch of > electrolytics! It should be easy to set the carrier detection bandwidth to > be a fraction of the information bandwidth so that reliable carrier > recovery can be maintained under any conditions under which the BPSK data > could be recovered. > > (An example of an 8-capacitor "Roanoake" type SCF may be seen here: > http://ka7oei.com/emm2a_scf.html ) > > This recovered (and slightly filtered) signal, divided-by-two, could then > be used to synchronously demodulate the original frequency-converted > signal, at which point one should have a reasonable representation of the > phase (and amplitude) of the transmitted signal - albeit, delayed by a > fairly consistent amount. > > Of course, all of this could be done by throwing a 16 bit A/D and DSP chip > at it, but sometimes there's a simple pleasure in doing it with a bunch of > 4000 CMOS and a few op-amps, handing the recovered baseband off to a PIC or > Arduino only at the very end! > > * * * > > Many years ago I built a WWVB carrier recovery circuit using just a > single-stage LC bandpass filter (to get rid of the VLF powerhouses) and an > NE565 phase detector along with a 6 MHz VCXO divided down to 60 kHz as the > comparison. What amazed me was that even with the practically nonexistant > filtering in front of the '565 (you really couldn't see the 60 kHz carrier > with the oscilloscope) that '565 would always find its way into lock over > time - and then it would stay firmly there owing to that effect that occurs > in which the effective loop bandwidth seems to decrease once lock has been > achieved. (WWVB's 45 degree phase shift "ID" would always throw it for a > loop, though - pun intended!) > > 73, > > Clint > KA7OEI > > > Date: Thu, 20 Feb 2014 22:10:26 -0500 >> From: paul swed<paulsw...@gmail.com> >> To: Discussion of precise time and frequency measurement >> <time-nuts@febo.com> >> Subject: Re: [time-nuts] New WWVB modulation format receivers >> Message-ID: >> <CAD2JfAhZvjSZ1vZiHBH05BwNc+DHd2gLQsTv1cAJc40UE1-gjw@mail. >> gmail.com> >> Content-Type: text/plain; charset=ISO-8859-1 >> >> >> Clint >> I don't know if it was me or not the said the doubling scheme did not >> work. >> It does work but profoundly unreliably at least on the east coast. If you >> miss one cycle of carrier you loose phase making it useless. Jfor here on >> Time nuts and I tried a lot of things to get around the issues because >> simple is best. Now I do know that folks much closer to wwvb use the >> doubling method. Someone posted that here. >> >> You brought up a really interesting comment on the mix down method and I >> have been curious about that and thinking about it. Especially since we >> are >> looking for a 1Hz phase flip. You mention the 60.003 crystal as an >> oscillator or filter? >> >> Very hard to get those today, not so as little as 5 years ago. I found an >> ebay supplier that sold something like 25 for $5 so picked up a pack >> hoping >> that some crystals would actually work as a filter in the RF chain and >> they >> actually do, but you actually have to hand pick them. As an oscillator >> pretty poor behavior. >> >> I have released a RF frontend design to time nuts some 6 months ago and >> also a traditional costas loop using cd 4000 series chips. It does work >> and >> does hold phase over multiple days. It can get tripped up. But all in all >> for literally a few dollars does well. But I absolutely believe there is a >> >> better way as you are suggesting. >> >> Regards >> Paul. >> WB8TSL >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.