Why is the marker Count Accuracy on the on the ESA Series Spectrum Analyzer only specified when using resolution bandwidths >1KHz?
When using RBWs less than 1KHz, the ESA is performing FFTs on the IF signal. However, Marker Count is counting the 21.4 MHz IF in a 1 kHz bandwidth, and does not have the discrimination of the FFT of the IF signal. As a result, if there is only one signal present, then the marker count will work properly in RBWs <= 300 Hz. If there are two or more signals present within 1kHz, then the counter will count incorrectly.
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