Hi
> On Jan 20, 2020, at 5:16 PM, jimlux <jim...@earthlink.net> wrote: > > On 1/20/20 1:57 PM, Attila Kinali wrote: > >> And then there ia third way, which is IMHO even better: >> Your application is an SDR system, i.e. you already need some >> signal processing for the system to work. Why not extend this >> to use it for the reference as well? Add another ADC and feed >> the reference signal to that, then track the phase/frequency >> relation between the sampling clock and the reference and >> compensate any drift in the signal path. This way you get to >> disable the reference if it is not needed and save a lot of power >> and at the same time are able to use references with any frequency >> and can change the "loop frequency" freely without the need to >> worry about PLL stability or tempco of filters in the multiplier >> version. > > This ... > > This is the way of the future. The problem is that there are enough legacy > systems out there where you need "control" vs "knowledge" > > And, in the SDR world: while theoretically, you can do this in software, a > lot of times the software is either a black box, or incomprehensible in > finite time, or architected in a way that makes it hard, that it's actually > faster and easier to discipline the reference oscillator than to fix the > software. If your “reference” is a 10 MHz OCXO, that may well come down on top / very near something you might want to receive. Having seen what WWV uses as an exciter … indeed their noise “as transmitted” is pretty darn good. If the reference is 16.384 …. hmmm …. maybe not so much. I can’t think of much around there worth tuning in to. Simply feeding the OCXO (at a very low level) into a single ADC might well do the trick. ( yes, you have a number of things to dig into, it’s not quite the slam dunk I’m making it out to be). Bob > > I say this as someone who makes his living designing, building, and using > SDRs - a Curse on Matt Ettus and USRPs, gnuradio, pothos, etc. and their ease > of use, allowing positive legions of people to produce software which is > horrible, without realizing the implications and defects within. They should > all be consulting *me* before engaging in these ill advised implementations > based on textbook descriptions from Oppenheim and Schaefer, etc. > > > But yes, the *best* way to do it is to *measure* the oscillator and use that > to correct the digitized data, rather than driving the oscillator. > It is challenging, though, to do this in a system where there is a need for > full duplex operation (i.e. the transmitted signal needs to be adjusted to > match the received signal). > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
