Transforming Cw Time Measurements Into The Frequency Domain; Forward Transform Measurements - Agilent Technologies 8753ET User Manual

Making Time Domain Measurements

Transforming CW Time Measurements into the Frequency Domain

Transforming CW Time Measurements into the Frequency Domain

The analyzer can display the amplitude and phase of CW signals versus time. For example, use this mode for
measurements such as amplifier gain as a function of warmup time (i.e. drift). The analyzer can display the
measured parameter (e.g. amplifier gain) for periods of up to 24 hours and then output the data to a digital
plotter for hardcopy results.
These "strip chart" plots are actually measurements as a function of time (time is the independent variable),
and the horizontal display axis is scaled in time units. Transforms of these measurements result in frequency
domain data. Such transforms are called forward transforms because the transform from time to frequency
is a forward Fourier transform, and can be used to measure the spectral content of a CW signal. For
example, when transformed into the frequency domain, a pure CW signal measured over time appears as a
single frequency spike. The transform into the frequency domain yields a display that looks similar to a
spectrum analyzer display of signal amplitude versus frequency.

Forward Transform Measurements

Figure 3-17 shows an example of a measurement using the Fourier transform in the forward direction, from
the time domain to the frequency domain.
Figure 3-17 Amplifier Gain Measurement
Interpreting the Forward Transform Vertical Axis
With the log magnitude format selected, the vertical axis displays dB. This format simulates a spectrum
analyzer display of power versus frequency.
Interpreting the Forward Transform Horizontal Axis
In a frequency domain transform of a CW time measurement, the horizontal axis is measured in units of
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