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| university:tools:pluto:users:phase_noise [10 Jun 2019 15:51] – [Frequency Stability] Robin Getz | university:tools:pluto:users:phase_noise [10 Jun 2019 16:01] – [Frequency Stability] Robin Getz |
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| The logarithmic x-axis corresponds to the observation time ("Tau"). Note that Tau is not the measurement time, but the evaluated time - the measurement lasts longer than Tau. Because the Rohde & Schwarz FSWP Phase Noise instrument calculates the Allan variance based on the measurement range of the phase noise measurement (offset frequency), the observation time corresponds to the measurement range and vice versa. | The logarithmic x-axis corresponds to the observation time ("Tau"). Note that Tau is not the measurement time, but the evaluated time - the measurement lasts longer than Tau. Because the Rohde & Schwarz FSWP Phase Noise instrument calculates the Allan variance based on the measurement range of the phase noise measurement (offset frequency), the observation time corresponds to the measurement range and vice versa. |
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| An alternative view of this is to look at stability over time with a [[wp>Spectrogram]]. A spectrogram is a visual representation of the spectrum of frequencies of a signal as it varies with time. This is a very intuative way to look at things, but it is not numerically precise, and is only a qualitative way to investigate things. For example, in the spectrogram below, a 502.001 MHz signal was output in the Pluto, we can see the signal drift over time. This drift is a measurement of the difference between the instrument (Tektronix [[https://www.tek.com/spectrum-analyzer/rsa5126b|RSA5126B]] Real Time Signal Analyzer, which is ±1ppm Initial accuracy) and the Pluto (which is ±25ppm Initial accuracy). The Pluto could be drifting, or the instrument could be drifting. The width of the drift is ~ 100 Hz over 60 minutes. For 500,000,000 Hz carrier, a 100 Hz drift is under .2 ppm. It should be noted that this is while the ADALM-PLUTO was allowed to warm up via self heating for 20 min before this measurement was recorded. | An alternative view of this is to look at stability over time with a [[wp>Spectrogram]]. A spectrogram is a visual representation of the spectrum of frequencies of a signal as it varies with time. This is a very intuative way to look at things, but it is not numerically precise, and is only a qualitative way to investigate things. For example, in the spectrogram below, a 502.001 MHz signal was output in the Pluto, we can see the signal drift over time. This drift is a measurement of the difference between the instrument (Tektronix [[https://www.tek.com/spectrum-analyzer/rsa5126b|RSA5126B]] Real Time Signal Analyzer, which is ±1ppm Initial accuracy) and the Pluto (which is ±25ppm Initial accuracy). The Pluto could be drifting, or the instrument could be drifting. The width of the drift is ~ 100 Hz over 60 minutes. For 500,000,000 Hz carrier, a 100 Hz drift is under 0.2 ppm. It should be noted that this is while the ADALM-PLUTO was allowed to warm up (via self heating) for 20 min before this measurement was recorded. This was approximately 1 hour of measurement. |
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| | {{ :university:tools:pluto:users:pluto_drift.png?800 |}} |
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