Last Updated: August 29, 2007
This measurement is only applicable with an IQ Capture license.
This topic describes the IQ Capture measurement. IQ Capture is a measurement in the RF Channel measurement suite.
This measurement provides a way to measure the magnitude/phase or real/imaginary components of a waveform. The raw IQ samples this measurement provides can then be used externally to compute customized measurement results. For example, results from this measurement can be used to characterize the magnitude and phase errors introduced by the non-linear effects of power amplifiers operating over a wide dynamic range. This measurement is very useful as it provides the flexibility needed to test virtually any type of waveform.
The IQ Capture measurement records either the magnitude/phase or real/imaginary components of the collected samples. The type of results returned depends on the setting of the IQ Capture Sample Format parameter.
If you have the IQ Capture Sample Format set to either Wrapped Polar or Unwrapped Polar the test set displays the magnitude results in linear units. To convert the magnitude results to:
units of mW, you
must square the magnitude results.
For example, if the test set returns an amplitude value of 10 this
corresponds to 100 mW (102=100).
units of dBm, you
must use the formula 20*log10(magnitude result).
For example, if the test set returns an amplitude value of 10 this
corresponds to 20 dBm (20*log10(10)=20).
If you have the IQ Capture Sample Format set to Rectangular the test set displays the magnitude results in linear units. The results can be converted to mW using the equation:
Real2 + Imaginary2
This measurement requires you to put your wireless device into a test mode that can command the wireless device to generate a waveform.
Before starting the measurement you should specify the wireless device's Frequency and the Expected Power on the test set's RF Analyzer. The Expected Power should be set to the maximum power level in the wireless device generated waveform, and the test set's RF Generator's Output Power should be set to Off.
The RF Rise or Immediate triggers can be used for triggering the measurement, however RF Rise is recommended in most instances.
For RF Rise triggering, it is recommended that the waveform starts with a suitable edge to trigger on. For example, a suitable signal would start with a pulse that is at the highest power level, this allows the RF Rise trigger to trigger at the start of that pulse. (An unsuitable waveform would be one that started with a long section of signal that was just at the RF Rise trigger threshold as this would make it difficult to determine where to trigger.)
The Immediate trigger is suitable for any signal that cannot be readily triggered using an RF Rise trigger.
This measurement can be armed as either a single or continuous measurement. Once triggered, the test set performs a measurement on the wireless device's generated waveform.
No averaging is available for this measurement. If the Multi-Measurement Count is set to a value greater than 1, the results returned are those for the last measurement.
For more information refer to How are the Measurements in the RF Channel Measurement Suite Made?.
IQ Capture is a measurement in the RF Channel measurement suite. See RF Channel Measurement Suite Setup Parameters for details of the parameters that apply to all measurements in the suite.
The Start Sample parameter allows you to select which measurement step is displayed at the top of the results table. Previous Page and Next Page allows you to tab through the measurement steps with each press displaying either the previous 25 samples or the next 25 samples respectively.
This result provides the integrity indicator for the RF Channel measurement suite. Normal indicates that the measurement suite completed successfully without error and the result is accurate. For details of other integrity indicators, see Measurement Integrity Indicator.
SCPI command: FETCh:RFCHannel:INTegrity?
These results provide the magnitude and phase of each measurement step. The magnitude results are displayed in linear units. For details on how to convert the results to mW or dBm refer to How is an IQ Capture Measurement Made?. The magnitude and phase results are displayed when the IQ Capture Sample Format is set to either Wrapped Polar or Unwrapped Polar.
SCPI command: FETCh:RFCHannel:IQCapture:TRACe[:PARTial]?
These results provide the real and imaginary magnitude measurement step. The results are displayed in linear units. For details on how to convert the results to mW refer to How is an IQ Capture Measurement Made?. The magnitude and phase results are displayed when the IQ Capture Sample Format is set to Rectangular.
SCPI command: FETCh:RFCHannel:IQCapture:TRACe[:PARTial]?
IQ Capture is a measurement in the RF Channel measurement suite. See RF Channel Input Signal Requirements for details of the input signal requirements that apply to all measurements in the suite.