Hi A lot depends on just how this or that was implemented. The bottom line is still that ionosphere issues will give you a “couple of milliseconds” sort of ill defined variation. If your RF chain is below 10 MS (which it likely is) is a bigger delay, but not a bigger variation.
Bob > On Dec 2, 2017, at 6:22 PM, jimlux <[email protected]> wrote: > > On 12/2/17 12:57 PM, Patrick Barthelow wrote: >> Just about to go across town to pick up TWO Radio Shack Timecube radios, >> that someone will sell cheap. Been 35 years since I have seen one. Used >> one in College to bring time to astronomy instruments in the field. >> From a newbie: Has anyone measured or does anyone have an idea of the >> propagation delay between an audio tick signal on the RF carrier at the >> antenna port, to an audio waveform on the demodulator/audio amp? >> Microseconds? more? less? >> If I hang a scope on the speaker audio out, and RF modulated input signal, >> how much delay would there be? Same question for an SDR. >> Best, 73, Pat Barthelow AA6EG >> apol <[email protected]>[email protected] > > > Milliseconds - mostly from the audio processing chain. For analog systems, > the delay is inversely proportional to bandwidth and proportional to number > of sections. > > In SDR implementations (obviously not the Timecube) the latency can be quite > long, and can be variable. Most SDR implementations don't pay much attention > to RF/Baseband delays as long as the pipeline doesn't run dry. > > > This was a big, big deal in the early days of the Flexradio, because it used > a half duplex processing chain with buffers - Tx/Rx turnaround could only > occur on a buffer boundary, and if you cranked the bandwidth down (for CW), > the buffer had to be fairly big. > > > Gnuradio and Pothos (two popular frameworks for SDR) don't really have any > provision for accurate timing - they're basically "signal flow graph" based > systems, and the latency through a block is whatever the software gives you. > > The USRP, in the usual "RF up/downconverter from digital samples" mode is > also noncoherent between RF and digital side - there's buffering in the USB > or Ethernet interfaces. > > The RTL-SDR pod is "coherent within a stream" - that is, once you're > streaming, there aren't any dropped samples, but the absolute timing between > RF sample and a particular USB data packet is uncertain (due to USB device > driver stuff). > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
