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Concepts

IQ Analysis Concepts

Purpose

IQ Analysis (Basic) mode is used to capture complex time domain data from wide

bandwidth RF signals. This mode preserves the instantaneous vector relationships of

time, frequency, phase and amplitude contained within the selected digitizer span or

analysis BW, at the analyzer's center frequency, for output as IQ data. This IQ data

can then be utilized internally or output over LAN, USB or GPIB for use with

external analysis tools. Each measurement description specifies the types of data

available remotely for that measurement.

Within the IQ Analyzer mode, basic frequency domain, time domain and IQ

measurements are available as initial signal and data verification tools in preparation

for deriving the IQ data output. This is accomplished using the Complex Spectrum

and IQ Waveform measurements. Although Complex Spectrum and IQ Waveform

are defined as measurements in the IQ Analyzer (Basic) mode, they act primarily as

tools to verify the signals and data as stated above.

Complex Spectrum measurement

Purpose

This measurement is FFT (Fast Fourier Transform) based. The FFT-specific

parameters are located in the Advanced menu. The Complex Spectrum

measurement provides a display in the upper window of power versus frequency

with current (yellow trace) and average (blue trace) data. In addition, an IQ

waveform of voltage versus time is provided in the lower window. One advantage of

having an I/Q view available while in the spectrum measurement is that it allows you

to view complex components of the same signal without changing settings or

measurements.

Measurement method

The measurement uses digital signal processing to sample the input signal and

convert it to the frequency domain. With the instrument tuned to a fixed center

frequency, samples are digitized at a high rate, converted to I and Q components with

DSP hardware, and then converted to the frequency domain with FFT software.

Troubleshooting hints

Changes made by the user to advanced spectrum settings, particularly to ADC range

settings, can inadvertently result in spectrum measurements that are invalid and

cause error messages to appear. Care needs to be taken when using advanced

features.

Keysight x-series Measurement Guide

Other manuals for Keysight x-series