User`s guide

Chirp
5-67
the chirp output when the Frequency Sweep parameter is set to Linear,
Quadratic, or Logarithmic.
For instance, if you want a chirp signal with a linear instantaneous frequency
sweep, you should set the
Frequency Sweep parameter to Linear, and tune
the linear sweep values by setting other parameters appropriately. The block
will output a chirp signal, the phase derivative of which is the specified linear
sweep. This ensures that the instantaneous frequency of the output is the
linear sweep you desired. For equations describing the linear, quadratic, and
logarithmic sweeps, see “Equations for Output Computation” on page 5-65.
Output Computation Method for Swept Cosine Frequency Sweep. To generate the swept
cosine chirp signal, the block sets the swept cosine chirp output as follows.
Note that Equation 5-1 does not hold for the swept cosine chirp, so the
user-defined frequency sweep, f
i
(t), is not the actual output frequency sweep,
f
i(actual)
(t), of the swept cosine chirp. Thus, the swept cosine output may not
behave as you expect. To learn more about swept cosine chirp behavior, see
“Cautions Regarding the Swept Cosine Sweep” on page 5-67 and “Equations for
Output Computation” on page 5-65.
Cautions Regarding the Swept Cosine Sweep
If you want a linearly swept chirp signal, we recommend you use a linear
frequency sweep. Though a swept cosine frequency sweep also yields a linearly
swept chirp signal, the output may have unexpected frequency content. For
details, see the following two sections.
Linear, quadratic, or logarithmic chirp
signal with phase
Phase derivative is instantaneous
frequency
(5-1)
Swept cosine chirp
output (Equation 5-1
does not hold.)
y
chirp
t() ψt() φ
0
+()cos=
ψ t()
f
i
t()
1
2π
------
dψ t()
dt
---------------
⋅=
y
chirp
t() ψt() φ
0
+()cos 2πf
i
t()t φ
0
+()cos==