I+jQ Frequency Spectrum

The frequency spectrum seen when an I+jQ channel configuration is selected contains both positive and negative frequencies. The negative frequencies are a result of the baseband frequency spectrum of the I and Q signals which has energy at both the positive and negative frequencies. The I+jQ Spectrum trace effectively shows the output spectrum of a mixer whose local oscillator set to 0 Hz (dc) and input is the baseband I/Q signal.

When an external converter is used, set the external center frequency to match the measurement center frequency and enable Frequency Converter. If Frequency Converter is not enabled, the displayed frequency axis represents frequencies relative to the center frequency at the downconverter and not the measurement's absolute center frequency.

The External downconverter IF must be set to 0 Hz.

$image\Ch1Ch2_NegFreq_wmf.jpg$