Re: [time-nuts] 3 corner hat for phase noise
Hello, I asked for a 3 corner hat measurement for phase noise. Managed to work it out myself. In case anyone else wants to know: First of all Timepod does do it but only for Allan Deviation. But I wanted it for phase noise. So if you make three phase noise measurements A vs B (call result X), A vs C (call result Y), B vs C (call the result Z) So you have three results X, Y, Z in dB. Then you do the following. Divide the dB by 10 Antilog them Then Osc A = (X+Y-Z)/2 Osc B = (X+Z-Y)/2 Osc C = (Y+Z-X)/2 Then log10 the above three results Then multiply by 10 to get back to phase noise in dB. So I made three measurements and got -115 dB, -114 dB and -113 dB The individual phase noise of each oscillator worked out to be -119.72, -116.78 and -115.35 The results are only accurate when the 3 oscillators are within 3 to 5 dB of each other, so its just an approximation. Regards Martyn ___ 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] 3 corner hat for phase noise
Hello, Does anyone have an EXCEL spreadsheet that calculates the individual phase noise of 3 oscillators when they are compared against each other, e.g A vs B, A vs C, B vs C. I.e the 3 corner hat technique. I do have a Timepod and I thought Timelab could do that, have haven't found how to do that. Regards Martyn ___ 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] 3 corner hat for phase noise
This is from 3hat.c -- C code, but you get the idea: A[i] = sqrt( (0 + SQUARE(AB[i]) - SQUARE(BC[i]) + SQUARE(AC[i])) / 2.0 ); B[i] = sqrt( (0 + SQUARE(AB[i]) + SQUARE(BC[i]) - SQUARE(AC[i])) / 2.0 ); C[i] = sqrt( (0 - SQUARE(AB[i]) + SQUARE(BC[i]) + SQUARE(AC[i])) / 2.0 ); And watch out for negative square roots. /tvb - Original Message - From: Martyn Smith mar...@ptsyst.com To: time-nuts@febo.com Sent: Tuesday, August 25, 2015 9:36 AM Subject: [time-nuts] 3 corner hat for phase noise Hello, Does anyone have an EXCEL spreadsheet that calculates the individual phase noise of 3 oscillators when they are compared against each other, e.g A vs B, A vs C, B vs C. I.e the 3 corner hat technique. I do have a Timepod and I thought Timelab could do that, have haven't found how to do that. Regards Martyn ___ 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] 3 corner hat for phase noise
Actually, after typing all that, it occurred to me that you might have actually meant to ask about N-cornered stability measurements. They aren't supported by the current official release of TImeLab; you need to use the beta version from http://www.miles.io/timelab/beta.htm . For instructions, hit 'e' to bring up the Trace Properties dialog box and move your mouse cursor over the 'Source A/Source B' fields. These allow you to add channel labels to existing .tim files. For TimePod acquisitions, it's easier to name the sources at acquisition time. Hover over the 'Ch 0/Ch 1/Ch 2' and 'Stability' fields on the Advanced tab of the acquisition dialog to see how to do that. Contrary to what the help text says, the TimeLab manual hasn't yet been updated, so the help text is all there is, as far as documentation goes. -- john, KE5FX Miles Design LLC One nice thing about phase noise is that it's computable with complex FFTs, rather than the one-dimensional phase or frequency differences that ADEV uses... ___ 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] 3 corner hat for phase noise
One nice thing about phase noise is that it's computable with complex FFTs, rather than the one-dimensional phase or frequency differences that ADEV uses. Another nice thing is that it's stationary -- meaning its probability distribution can (usually) be treated as unchanging from one measurement to the next. These two properties allow PN measurements to be performed with vector averaging over time, resulting in a single correct value at each bin. Unlike a stability measurement, the expectation with PN is that repeated measurements will always yield the same plot. So you don't need to use statistical hacks like N-corner hats to measure phase noise with a TimePod or other multichannel instrument. Pull the SMA jumpers off of the Ch0 and Ch2 jacks and feed two independent references to them. Over time, the measurement will converge to the phase noise of the source at the REF IN jack, even if it is quieter than either of the two sources at the input jacks. The TimePod/3120A firmware can't compensate for frequency offsets between Ch0 and Ch2, so the two independent sources need to be very close in frequency and they need to stay that way over the course of the measurement. A pair of good-quality rubidium or GPS clocks can be a good way to go. -- john, KE5FX Miles Design LLC -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Tom Van Baak Sent: Tuesday, August 25, 2015 11:11 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] 3 corner hat for phase noise This is from 3hat.c -- C code, but you get the idea: A[i] = sqrt( (0 + SQUARE(AB[i]) - SQUARE(BC[i]) + SQUARE(AC[i])) / 2.0 ); B[i] = sqrt( (0 + SQUARE(AB[i]) + SQUARE(BC[i]) - SQUARE(AC[i])) / 2.0 ); C[i] = sqrt( (0 - SQUARE(AB[i]) + SQUARE(BC[i]) + SQUARE(AC[i])) / 2.0 ); And watch out for negative square roots. /tvb - Original Message - From: Martyn Smith mar...@ptsyst.com To: time-nuts@febo.com Sent: Tuesday, August 25, 2015 9:36 AM Subject: [time-nuts] 3 corner hat for phase noise Hello, Does anyone have an EXCEL spreadsheet that calculates the individual phase noise of 3 oscillators when they are compared against each other, e.g A vs B, A vs C, B vs C. I.e the 3 corner hat technique. I do have a Timepod and I thought Timelab could do that, have haven't found how to do that. Regards Martyn ___ 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.
