niRFSG Fractional Resampling
Resamples and/or realigns a complex-valued waveform that you specify. This VI has three polymorphic instances, which take as data input a Complex Cluster, a Complex Waveform, or an I-Q Array.
Supported Devices: NI 5670/5671/5672
Use the pull-down menu to select an instance of this VI.
niRFSG Fractional Resampling (Complex Input)
Inputs a complex-valued waveform and resamples and/or realigns it based on the input parameters that you specify. To realign the input waveform in time, enter a nonzero value in the initial sample offset parameter. Positive or negative offset values push the output complex waveform forward or backward in time, respectively, relative to the input complex waveform.
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initial sample offset (sec) specifies the alignment of the input waveform in time. To realign the input waveform in time, enter a nonzero value in this parameter. Positive or negative offset values push the output complex waveform forward or backwards in time, respectively, relative to the waveform data specified in the input complex waveform parameter. |
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desired sample rate (Hz) specifies the desired sample rate of the output complex waveform data, expressed in Hz. This value can be an integer or a non-integer multiple of the input data sample rate. The default value is 100 MHz. |
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input complex waveform specifies the complex baseband waveform data.
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reset? (T) specifies whether the VI continues resampling using the previous iteration states. reset? (T) must be set to TRUE (default) whenever you want to restart fractional resampling. |
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error in accepts error information from previously called VIs. The pop-up option Explain Error (or Explain Warning) gives more information about the error displayed.
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output complex waveform returns the resampled complex baseband waveform data.
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error out passes error or warning information out of a VI to be used by other VIs. The pop-up option Explain Error (or Explain Warning) gives more information about the error displayed.
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niRFSG Fractional Resampling (CWDT)
Inputs a complex-valued waveform and resamples and/or realigns it based on the input parameters that you specify. To realign the input waveform in time, enter a nonzero value in initial sample offset. Positive or negative offset values push the output complex waveform forward or backwards in time, respectively, relative to input complex waveform.
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initial sample offset (sec) specifies the alignment of the input waveform in time. To realign the input waveform in time, enter a nonzero value in this parameter. Positive or negative offset values push the output complex waveform forward or backwards in time, respectively, relative to the waveform data specified in the input complex waveform parameter. |
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desired sample rate (Hz) specifies the desired sample rate of the output complex waveform data, expressed in Hz. This value can be an integer or a non-integer multiple of the input data sample rate. The default value is 100 MHz. |
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input complex waveform specifies the complex baseband waveform data. |
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reset? (T) specifies whether the VI continues resampling using the previous iteration states. reset? (T) must be set to TRUE (default) whenever you want to restart fractional resampling. |
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error in accepts error information from previously called VIs. The pop-up option Explain Error (or Explain Warning) gives more information about the error displayed.
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output complex waveform returns the resampled complex baseband waveform data.
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error out passes error or warning information out of a VI to be used by other VIs. The pop-up option Explain Error (or Explain Warning) gives more information about the error displayed.
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niRFSG Fractional Resampling (I-Q)
Inputs a complex-valued waveform and resamples and/or realigns it based on the input parameters that you specify. To realign the input waveform in time, enter a nonzero value in initial sample offset. Positive or negative offset values push the output complex waveform forward or backwards in time, respectively, relative to input complex waveform.
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initial sample offset (sec) specifies the alignment of the input waveform in time. To realign the input waveform in time, enter a nonzero value in this parameter. Positive or negative offset values push the output complex waveform forward or backwards in time, respectively, relative to the waveform data specified in the input complex waveform parameter. |
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desired sample rate (Hz) specifies the desired sample rate of the output complex waveform data, expressed in Hz. This value can be an integer or a non-integer multiple of the input data sample rate. The default value is 100 MHz. |
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I specifies the in-phase (I) component of the complex baseband signal. |
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Q specifies the quadrature-phase (Q) component of the complex baseband signal. |
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input sample rate specifies the sample rate, in hertz, of the input data. |
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reset? (T) specifies whether the VI continues resampling using the previous iteration states. reset? (T) must be set to TRUE (default) whenever you want to restart fractional resampling. |
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error in accepts error information from previously called VIs. The pop-up option Explain Error (or Explain Warning) gives more information about the error displayed.
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I out returns the resampled complex baseband I data. |
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Q out returns the resampled complex baseband Q data. |
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error out passes error or warning information out of a VI to be used by other VIs. The pop-up option Explain Error (or Explain Warning) gives more information about the error displayed.
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Details
To resample a waveform, enter a desired sample rate that differs from the existing sample rate of the input complex waveform parameter. To realign a waveform without changing the sample rate, specify a desired sample rate parameter value equal to the existing sample rate. To resample a waveform without changing the relative timing offset between the input and output complex waveforms, specify an initial sample offset parameter value of 0.
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Note The sample rate of your waveform corresponds to the IQ rate property in RFSG. |
Resampling and Phase Continuity
Resampling can disturb phase continuity. For example, if a sine wave sampled at 4 samples per cycle in a 4-sample long phase-continuous array, is resampled at a rate of 4.5 samples per cycle, the resulting 5 samples are no longer phase-continuous. Phase continuity is only preserved if an integer number of samples in the original array becomes an integer number of samples in the resampled array. The following figure shows a 4-sample waveform resampled to 4.5 samples. The rate change should produce 4.5 samples, but only an integer number of samples can be returned by the resampler.
Address this issue by repeating the original array. If the original array is copied and concatenated, there are 8 samples in the new phase-continuous array. The frequency content of the new array is exactly the same as the frequency content of the original array. If resampling is performed from 4 to 4.5 samples per cycle, the 8 samples becomes 9 samples. Because 9 is an integer, phase continuity is preserved. This strategy is shown in the Resample and Write example for NI-RFSG. The following figure shows both sample rates phase-continuous on two waveform cycles.
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Note You can use the rfsg_Resample and Write VI to ensure that the signal's phase continuity is maintained while resampling. |