Re: [time-nuts] Phase noise from Allan Deviation ?
Hi Iain, I'll publish a flowgraph soon. I built a Out-Of-Tree module to decimate the output down to one sample per reading to keep the output file small for even long runs. On the order of about 48000:! decimation. Strange thing is - it works when the QT Time Sink is enabled, but gives very wrong outputs when the QT Time Sink is Disabled (the only change). So I suspect my custom OOT is doing something wrong, but not sure why enabling/disabling the scope display changes the gnuradio behavior so much. I'd like to get more to the bottom of this before publishing the code. Have done some short runs throwing 48,000 samples/sec to the output file, then post processing that in Python, and it gives the same results as my OOT module when the QT GUI is showing. Very strange, but the data file is much too verbose: 700 Megabytes/hour. -- Tom, N5EG On Mon, Dec 14, 2015 at 1:15 AM, Iain Young wrote: > Hi Tom, > > On 14/12/15 03:15, You wrote: > > I've constructed a homebrew setup to measure time intervals using a >> software defined radio. Basically a single-channel downconversion to >> about one hertz, then count samples from the SDR clock to time stamp >> the zero crossings. This is done in gnuradio and saved to a file for >> post processing. The resolution is theoretically good, but the accuracy >> is unknown. >> > > Very interesting. Would you consider making your flowgraph available ? > > I have done similar things with just thresholding and looking for the > start of second (or minute) marker of various distant radio clocks, and > then graphing how far apart they were, as well as feeding NTP. > > > 73s > > Iain > > > ___ > 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.
Re: [time-nuts] Mechanical clock sound pickup circuit
This may be totally ridiculous, but maybe there's another way to get a balance wheel signal. The X-band Doppler type microwave motion detectors can pick up various object signals in free air from quite a distance, so maybe up close there would be enough resolution and penetration of the metal parts of a timepiece to get a usable signal in and out. It would tend to accentuate the fastest part of any motion - the balance wheel in this case. I can picture setting one up with the horn pointed at the thinnest part, likely the watch face, from maybe a few inches away - or whatever it takes to not overload the detector. The audio detector signal (if sufficient) could then be processed in the same way as with a microphone sound signal. Ed ___ 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.
Re: [time-nuts] Mechanical clock sound pickup circuit
On 12/14/15 9:12 PM, ed breya wrote: This may be totally ridiculous, but maybe there's another way to get a balance wheel signal. The X-band Doppler type microwave motion detectors can pick up various object signals in free air from quite a distance, so maybe up close there would be enough resolution and penetration of the metal parts of a timepiece to get a usable signal in and out. It would tend to accentuate the fastest part of any motion - the balance wheel in this case. I can picture setting one up with the horn pointed at the thinnest part, likely the watch face, from maybe a few inches away - or whatever it takes to not overload the detector. The audio detector signal (if sufficient) could then be processed in the same way as with a microphone sound signal. As it happens, I have a fair amount of recent experience detecting small (<1mm) motions using radar. Yes, remarkably tiny holes will let enough signal in and out, but, it's going to be very, very position dependent. You have a lot of multipath in this kind of testing, and it's easy to wind up in a null zone. You might want to look for K-band (24GHz) units: the shorter the wavelength, the more phase shift you get from the tiny motion. To put some numbers on it: at 3 GHz, a 1mm displacement gives you about 6-7 degrees; at 24 GHz, you're going to be getting 50-60 degrees. You'll be wanting some form of homodyne detector (which has the nice property that the phase noise of the source cancels out, so you can have a pretty grungy quality oscillator). The signal you're looking for, though, is phase shifts occurring at a 1Hz kind of rate. Most of the cheap "motion detectors" have a high pass filter (1 m/sec at 3 cm wavelength is 66 Hz) and the amplifier chain is AC coupled. You'll need a good low noise amplifier with a low 1/f knee. For reference, a receiver gain of about 60 dB gives you a millivolt kind of signal from a 1mm displacement with 1mW at 3GHz from a 0.1 square meter target at 10 meter distance. You can scale to your situation. You'll probably want some way to subtract out the static baseline, so your high gain amplifier stages don't need enormous dynamic range. In my radars, I do this with an adjustable "leakage" path from Tx to Rx. You could probably do it with a movable metal target next to your clock/watch and you adjust it for a null. You probably also want a I/Q output: if you think about the signal you're receiving, it's a slowly moving vector that spans a fairly small phase angle (because it combines a very large static response from stuff that's moving plus a little tiny moving component). If that vector happens to point at 90 degrees to your I axis only, then you're great: the variation shows up in the I axis. But if the vector happens to point parallel to the I axis, the motion is very small. With I/Q, you can either do a arctan demodulation, or you can rotate the signal to make the variation largest (basically using the sin x=x approximation for small x) Ed ___ 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.
Re: [time-nuts] Mechanical clock sound pickup circuit
Let's be serious here. Radar is the wrong part of the E-M spectrum. Use light. It is cheap, easy to detect, and there are plenty of reflections to go around. Or better still, listen to the tic. Then you don't even have to open the case Which brings this full circle. -Chuck Harris Jim Lux wrote: On 12/14/15 9:12 PM, ed breya wrote: This may be totally ridiculous, but maybe there's another way to get a balance wheel signal. The X-band Doppler type microwave motion detectors can pick up various object signals in free air from quite a distance, so maybe up close there would be enough resolution and penetration of the metal parts of a timepiece to get a usable signal in and out. It would tend to accentuate the fastest part of any motion - the balance wheel in this case. I can picture setting one up with the horn pointed at the thinnest part, likely the watch face, from maybe a few inches away - or whatever it takes to not overload the detector. The audio detector signal (if sufficient) could then be processed in the same way as with a microphone sound signal. As it happens, I have a fair amount of recent experience detecting small (<1mm) motions using radar. Yes, remarkably tiny holes will let enough signal in and out, but, it's going to be very, very position dependent. You have a lot of multipath in this kind of testing, and it's easy to wind up in a null zone. You might want to look for K-band (24GHz) units: the shorter the wavelength, the more phase shift you get from the tiny motion. To put some numbers on it: at 3 GHz, a 1mm displacement gives you about 6-7 degrees; at 24 GHz, you're going to be getting 50-60 degrees. You'll be wanting some form of homodyne detector (which has the nice property that the phase noise of the source cancels out, so you can have a pretty grungy quality oscillator). The signal you're looking for, though, is phase shifts occurring at a 1Hz kind of rate. Most of the cheap "motion detectors" have a high pass filter (1 m/sec at 3 cm wavelength is 66 Hz) and the amplifier chain is AC coupled. You'll need a good low noise amplifier with a low 1/f knee. For reference, a receiver gain of about 60 dB gives you a millivolt kind of signal from a 1mm displacement with 1mW at 3GHz from a 0.1 square meter target at 10 meter distance. You can scale to your situation. You'll probably want some way to subtract out the static baseline, so your high gain amplifier stages don't need enormous dynamic range. In my radars, I do this with an adjustable "leakage" path from Tx to Rx. You could probably do it with a movable metal target next to your clock/watch and you adjust it for a null. You probably also want a I/Q output: if you think about the signal you're receiving, it's a slowly moving vector that spans a fairly small phase angle (because it combines a very large static response from stuff that's moving plus a little tiny moving component). If that vector happens to point at 90 degrees to your I axis only, then you're great: the variation shows up in the I axis. But if the vector happens to point parallel to the I axis, the motion is very small. With I/Q, you can either do a arctan demodulation, or you can rotate the signal to make the variation largest (basically using the sin x=x approximation for small x) Ed ___ 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.
