Hi … because some want to keep the old stuff going. It's a hobby.
Indeed my interest would mainly be in simply building a new (cheap) receiver. Bob On Jul 7, 2012, at 12:22 PM, J. Forster wrote: > Why bother? > > If you have to build/buy a new receiver to make your old receiver work, > why not just use the new receiver? > > YMMV, > > -John > > =============== > > >> Hi >> >> It *may* turn out to be easier to receive and demodulate the new signal, >> then use it to de-bpsk the signal to an older box than to try to strip the >> bpsk. I agree that they may not change anything, but I'd hate to get it >> all running and have them make a change. >> >> Bob >> >> On Jul 7, 2012, at 11:30 AM, paul wrote: >> >>> >>> Pretty sure NIST will not do anything. Just to set expectations. >>> We are fortunate that to some extent John Lowe is responding to >>> questions. >>> But we are on our own. >>> I think the big lesson I have already learned is that there are lots of >>> standard approaches to solving the problem Micros FPGAs dpll pll..... >>> But the fun comes in when you account for the 17 db amplitude variation >>> for modulation. With propagation, with BPSK and sprinkle in noise thats >>> higher in level then the signal that contains impulse and random crud. >>> >>> Now that starts to become really a lot of fun. >>> I already built a much larger antenna 10 ft by 10 ft loop 25 turns... >>> Lot of gain added. >>> Regards >>> Paul >>> >>> >>> On 7/6/2012 11:28 AM, Bob Camp wrote: >>>> Hi >>>> >>>> My *guess* is that $50 is in the ball park for parts cost of a pretty >>>> good receiver for the new format. That does not include things like the >>>> external standard, antenna, frequency comparison stuff, power or case. >>>> I'd bound the range of the guess as $25 to $100. >>>> >>>> Bob >>>> >>>> On Jul 5, 2012, at 11:56 PM, J. Forster wrote: >>>> >>>>>> On Thu, Jul 05, 2012 at 04:19:25PM -0700, J. Forster wrote: >>>>>>> If propagation goes south, you loose track of the carrier phase, the >>>>>>> basis >>>>>>> of the system. If your local standard is stable and close to right, >>>>>>> that's >>>>>>> not a big deal. If not, you can easily go down the garden path. >>>>>> If I read this correctly, you mean you have a 180 degree >>>>>> ambiguity due to the BPSK - obviously losing track of the carrier >>>>>> phase >>>>>> in general with a significantly wrong local standard loses... >>>>> David, >>>>> >>>>> Most of what has been tried is an analog squareing, then a divide by >>>>> two. >>>>> No additional PLLs in the system, beyond what is already in the Rx. >>>>> >>>>>> I have not devoted enough time to this to be absolutely sure but >>>>>> it sure sounds like from what I read that if you know the accurate >>>>>> time >>>>>> to one second it should be possible to unambiguously predict the >>>>>> carrier >>>>>> phase sequences simply because you know the message format exactly, >>>>>> AND >>>>>> you know the exact time of day message that is being transmitted or >>>>>> most >>>>>> of it. >>>>> The BPSK rate is 1 bit per second, There are 120,000 half cycles in >>>>> that >>>>> time. Fades can last seconds, minutes, or hours. It comes down to how >>>>> long >>>>> does it take your local standard take to drift roughly 4 uS. >>>>> >>>>> At the moment we are not looking at the message at all. >>>>> >>>>> Certainly a correlating receiver that uses the message as well as the >>>>> carrier could be built. But, IMO, that'd be a whole lot easier done >>>>> from >>>>> scratch with a micro. The object here is a small, fairly simple, >>>>> retrofit >>>>> for the existing receivers. The message format may not be fully >>>>> defined as >>>>> yet. The squareing approach is message independant. >>>>> >>>>>> There are of course two forms of encoding in PSK modulations - >>>>>> absolute, and differential (or transition) ... naively to me it would >>>>>> seem that if absolute encoding is used for this and you know most of >>>>>> the >>>>>> bits of the message most of the time you could predict which phase >>>>>> will >>>>>> be used a lot of the time, and also know when you don't know (message >>>>>> bits you might be uncertain about)... >>>>> If you used the signal to set your local clock, and knew the format, >>>>> it >>>>> should be easy to predict at least a good part, if not all, of the >>>>> message. >>>>> >>>>>> Differential encoding has the down side for this that UNLESS you >>>>>> know all previous message bits accurately starting from some phase >>>>>> reference datum you cannot predict what phase is in use at a >>>>>> particular >>>>>> moment. Absolute encoding (eg 0 phase for a 0, 180 for a one) >>>>>> doesn't >>>>>> have that liability and if the time of day message is aligned to, >>>>>> well, >>>>>> the time of day if you know that with reasonable accuracy (and you do >>>>>> since you are being sent it in the first place) you should be able to >>>>>> predict a very large percentage of phases used accurately. >>>>>> >>>>>> Again, deferring to those who have done the experiments (which I >>>>>> have clearly not), it would seem that the ability to predict the >>>>>> phase >>>>>> most of the time would allow creation of a reliable local 60 KHz >>>>>> reference which could be used to disambiguate those bits you don't >>>>>> know >>>>>> apriori >>>>>> >>>>>> My naive scheme would be to drive a balanced modulator on the >>>>>> output of the 60 KHz loop antenna with either two or maybe three >>>>>> values >>>>>> (1 and -1 or 1, 0 and -1) using some cheapie micro (Arduino, PIC >>>>>> etc) >>>>>> with a software PLL to keep the bit timing in sync with the signal. >>>>> This is what Equatorial did, in TTL, 30+ years ago. >>>>> >>>>>> For bits that one could not predict, one could either output 0 >>>>>> to the balanced modulator for the entire bit interval which would >>>>>> produce a drop in the 60 KHz carrier, or do a fast timed fraction of >>>>>> a >>>>>> bit look at the output of a synchronous detector and choose the most >>>>>> likely value for the bit and use that, maybe after a brief 0 no >>>>>> carrier >>>>>> interval to avoid a detectable phase glitch. >>>>>> >>>>>> Of course the other approach is to start with the assumption you >>>>>> have a pretty good stable source of clock or you would not be doing >>>>>> this >>>>>> to begin with, and simply A/D the 60 KHz with the stable clock (say >>>>>> at >>>>>> 10 MHz), delay it by storing samples in RAM for one bit time of the >>>>>> low >>>>>> speed code and use that entire interval to decide which phase you >>>>>> were >>>>>> seeing and suitably adjust the output phase accordingly when you spit >>>>>> out the samples delayed by one bit time. >>>>>> >>>>>> This later approach would certainly be doable with modern >>>>>> processors mostly in software, certainly so if you could live with >>>>>> say 1-2 >>>>>> MHz sampling of the 60 KHz or so... and quite possibly also pretty >>>>>> nicely with a modest FPGA complete with the sample storage in the >>>>>> chip. >>>>>> >>>>>> Both approaches would be helped a lot if the architecture of the >>>>>> system allows prediction of absolute phase (eg not differential >>>>>> encoding >>>>>> of unpredictable messages)... and AFAIK that is not yet set in stone >>>>>> and >>>>>> could be changed to allow this. >>>>>> >>>>>> The intent of both of these schemes would be to ultimately >>>>>> output a De-psk'd signal that older equipment could process using its >>>>>> antique analog circuitry without serious issues. Thus the output >>>>>> would be an attempt at a phase stable corrected version of the >>>>>> original >>>>>> signal... >>>>> This is what NIST is planning, I think. Make a new receiver, then >>>>> synthesizing 60 kHz from the internal locked clock. It's kinda like a >>>>> TV >>>>> 'Converter Box'. It will continue to provide the functionallity, but >>>>> at >>>>> what price? At $50 it would be a good deal; at $5000 not so much, IMO. >>>>> >>>>> -John >>>>> >>>>> ================= >>>>> >>>>> >>>>> >>>>>> Certainly using a lab reference stable 10 MHz derived 960 Khz >>>>>> or whatever sampling clock to delay the signal one time code bit time >>>>>> should not produce significant 60 KHz phase wanderings at all... >>>>>> >>>>>> -- >>>>>> Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, >>>>>> Mass >>>>>> 02493 >>>>>> "An empty zombie mind with a forlorn barely readable weatherbeaten >>>>>> 'For Rent' sign still vainly flapping outside on the weed encrusted >>>>>> pole - >>>>>> in >>>>>> celebration of what could have been, but wasn't and is not to be now >>>>>> either." >>>>>> >>>>>> >>>>> >>>>> >>>>> _______________________________________________ >>>>> 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. >>> >>> >>> >>> _______________________________________________ >>> 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. >> >> > > > > _______________________________________________ > 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.