User`s guide

Chirp
5-68
Swept Cosine Instantaneous Output Frequency at the Target Time is not the Target Frequency.
The swept cosine sweep value at the Target time is not necessarily the Target
frequency
. This is because the user-specified sweep is not the actual frequency
sweep of the swept cosine output, as noted in “Output Computation Method for
Swept Cosine Frequency Sweep” on page 5-67. See Table 5-1, Instantaneous
Frequency Sweep Values, for the actual value of the swept cosine sweep at the
Target time.
Swept Cosine Output Frequency Content May Greatly Exceed Frequencies in the Sweep. In
Swept cosine mode, you should not set the parameters so that 1/T
sw
is very
large compared to the values of the
Initial frequency and Target frequency
parameters. In such cases, the actual frequency content of the swept cosine
sweep may be closer to 1/T
sw
, far exceeding the Initial frequency and Target
frequency
parameter values.
Examples The first few examples demonstrate how to use the Chirp block’s main
parameters, how to view the output in the time domain, and how to view the
output spectrogram:
•“Example 1: Setting a Final Frequency Value for Unidirectional Sweeps”
•“Example 2: Bidirectional Sweeps”
•“Example 3: When Sweep Time is Greater Than Target Time”
Examples 4 and 5 illustrate Chirp block settings that may produce unexpected
outputs:
•“Example 4: Output Sweep with Negative Frequencies”
•“Example 5: Output Sweep with Frequencies Greater Than Half the
Sampling Frequency”
Example 1: Setting a Final Frequency Value for Unidirectional Sweeps. Often times, you
may want a unidirectional sweep for which you know the initial and final
frequency values. You can specify the final frequency of a unidirectional sweep
by setting
Target time equal to Sweep time, in which case the Target
frequency
becomes the final frequency in the sweep. The following model
demonstrates this method.
This technique may not work for swept cosine sweeps. For details, see
“Cautions Regarding the Swept Cosine Sweep” on page 5-67.