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university:tools:pluto:users:phase_noise [10 Jun 2019 16:01] – [Frequency Stability] Robin Getz | university:tools:pluto:users:phase_noise [10 Jun 2019 16:22] (current) – Capitialization changes Travis Collins | ||
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In any transmitter (or receiver) design, frequency stability is of critical importance. Many are interested in both long-term and short-term stability. Long-term frequency stability is concerned with how the output signal varies over a long period of time (minutes, hours, days, or months). It is usually specified as the ratio, Δf/f for a given period of time, expressed as a percentage or in dB. These changes can be the results of thermal, aging, or voltage variations. | In any transmitter (or receiver) design, frequency stability is of critical importance. Many are interested in both long-term and short-term stability. Long-term frequency stability is concerned with how the output signal varies over a long period of time (minutes, hours, days, or months). It is usually specified as the ratio, Δf/f for a given period of time, expressed as a percentage or in dB. These changes can be the results of thermal, aging, or voltage variations. | ||
- | Short-term stability, on the other hand, is concerned with variations that occur over a period of seconds or less. These variations can be random or periodic, and are normally referred to a phase noise, measured in dBc/Hz. | + | Short-term stability, on the other hand, is concerned with variations that occur over a period of seconds or less. These variations can be random or periodic and are normally referred to as phase noise, measured in dBc/Hz. |
===== Frequency Stability ===== | ===== Frequency Stability ===== | ||
- | Frequency stability is a measure of how well a device is able to produce its a specific frequency over time without drifting from that frequency. | + | Frequency stability is a measure of how well a device is able to produce its a specific frequency over time without drifting from that frequency. |
- | The point of interest in the Allan Variance plot is the minimum of the curve. Normally in plots like this, the deviation is high, because of noise. Over longer observations times, the noise averages out until the minimum is reached. The minimum thus corresponds to the point in time when the deviation from the specified frequency is at its lowest. After that, the stability deteriorates due to drift, temperature effects and aging. In this case, we can see that the time that the Pluto SDR is most stable is over 10ms (100Hz) to 1 second (1Hz). Over this, there can be a slow drift that will effect | + | The point of interest in the Allan Variance plot is the minimum of the curve. Normally in plots like this, the deviation is high, because of noise. Over longer observations times, the noise averages out until the minimum is reached. The minimum thus corresponds to the point in time when the deviation from the specified frequency is at its lowest. After that, the stability deteriorates due to drift, temperature effects, and aging. In this case, we can see that the time that the Pluto SDR is most stable is over 10ms (100Hz) to 1 second (1Hz). Over this, there can be a slow drift that will affect |
- | {{ : | + | {{ : |
- | The logarithmic x-axis corresponds to the observation time (" | + | The logarithmic x-axis corresponds to the observation time (" |
- | An alternative view of this is to look at stability over time with a [[wp> | + | An alternative view of this is to look at stability over time with a [[wp> |
- | {{ : | + | {{ : |
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- | However, at lower frequencies (100 mHz, or over 10 seconds) to 100 kHz, we can see that the noise, or in this case drift, can vary quite a bit. This sub 100 kHz offset/ | + | However, at lower frequencies (100 mHz, or over 10 seconds) to 100 kHz, we can see that the noise, or in this case drift, can vary quite a bit. This sub 100 kHz offset/ |
{{ : | {{ : | ||
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===== Summary ===== | ===== Summary ===== | ||
- | Phase noise and drift are key parameters for many oscillators and signal sources as it governs many aspects of the overall performance. In modern communication systems many drift issues can be overcome with various signal processing algorithms. | + | Phase noise and drift are key parameters for many oscillators and signal sources as it governs many aspects of the overall performance. In modern communication systems, many drift issues can be overcome with various signal processing algorithms. |
===== More information ===== | ===== More information ===== |