On Wed, Feb 26, 2020 at 4:23 PM Heikki Laamanen <heikki.laama...@dlc.fi> wrote:
> > So you want to produce something like a stable 10MHz reference and a > 1PPS which is synchronous to UTC using broadcast/terrestrial signals such > as DVB-T, ATSC, LTE, etc? And your edges can be within +/-50ns of actual > UTC? > > > > Yes. All those signals (not sure about ATSC) are synchronized to UTC > directly (via GPS) or indirectly (via PTP over fiber). Thus, the signals > carry inherent timing information. There are naturally lots of issues > related with radio wave propagation in each case like multipath propagation > caused by reflections, groundwave/skywave phenomena concerning LF radio > wave propagation, e.g. DCF-77 and the ancient C-Loran. The most ideal cases > are line-of-sight wave paths like GPS satellite – GPS receiver. > > > > I have one more question. I have not found any GNU Radio object utilizing > the possibility of controlling the ADC sampling frequency via controllable > PLLs on the RF HW. All sync-related objects seem to use – e.g., polyphase > filters, for adjusting sampling phase. Am I right? > Some radios use a DAC to control a VCTCXO with a pullability of maybe +/-10ppm. Others use an analog PLL to lock to an externally supplied reference (like 10MHz or so). Most would probably want to keep jitter to a minimum and track the sampling offset digitally. You may want to look into what it might take to do that instead of expecting a clock to be perfect. Brian
