Time Data (Frequency)

The Time Data selection determines whether the time data used in a Vector measurement is complex data or real data.

When Baseband is selected, the measurement hardware's (digital or analog) local oscillator (LO) is removed from the RF Radio Frequency: A generic term for radio-based technologies, operating between the Low Frequency range (30k Hz) and the Extra High Frequency range (300 GHz). measurement path and the Start frequency is set to 0 Hertz. In this case, the VSA performs measurements on real-valued time data (no complex component).

Time Data can only be changed to Baseband for Vector measurements and when the measurement hardware for the selected input channel supports digitizing the input signal without an analog or digital LO in the path.

For other configurations, Time Data is always Zoom.

When Zoom is selected, the VSA performs measurements on complex time data. To obtain complex data, the VSA enables the measurement hardware's (digital or analog) LO. For measurement hardware that does not have an LO (such as oscilloscopes), the VSA performs the downconversion with its own digital LO.

Time Data automatically changes to Zoom when the Start frequency is set to a non-zero value. This also happens when you change the Span. To stay in Baseband mode when changing the Span, clear the Zoom If Span Change check box.

Baseband versus Zoom

The term "baseband" identifies a measurement that has real time-domain data. In Baseband mode, the signal is analyzed from 0 Hz to the highest frequency of interest. The term "zoom" identifies a measurement that has complex time-domain data. In zoomed mode, the signal is analyzed within a specified bandwidth, centered on the frequency of interest. Zoom measurements can start at 0 Hz or other frequencies.

The VSA performs zoomed measurements using a digital LO (local oscillator). In some cases, the digital LO is in hardware.

The measurement is "zoomed" when there is a (digital or analog) LO in the RF measurement path. In this case, the input signal is mixed with the LO, and the resulting time-domain data is complex--contains both a real and an imaginary component.

The measurement is "baseband" when there is no LO in the RF measurement path. In this case the input signal (after filtering) is sampled directly by the A/D converter, and the resulting time-domain data is real.