64 Chapter2
Making Measurements
Example 3: Modulation
4. Knowing that the desired deviation is 25 kHz, and choosing the
modulation index of the first carrier null, calculate the modulating
frequency as follows:
5. Set the modulation rate on the signal generator to 10.412 kHz. If the
signal source doesn't have an accurate internal modulation source,
use an external source. You can use the delta count mode of the
analyzer to accurately set the audio source frequency as follows:
Figure 2-11 Markers Show Modulating Frequency
Modulating Frequency
25kHz
2.401
----------------=
Modulating Frequency 10.412kHz=
Table 2-3
a. Press FREQ COUNT to activate the counter function, then press
COUNTER RES and set the counter resolution.
b. Press COUNTER ON OFF so that ON is underlined, and use the delta
count mode to read the difference between two sideband peaks (see
Figure 2-11).
c. Now adjust the frequency deviation for a maximum null of the carrier.
d. Calculate the FM deviation by multiplying the modulation index
(from Table 2-10) by the modulation rate:
e. FM Deviation = 10.39 kHz × 2.401
f. FM Deviation = 24.95 kHz
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