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Figure 4- 16 Select modulation source
1)
Internal source
In case of internal modulation source, modulation wave can be sine wave, square wave, sawtooth wave and arbitrary
wave, and is sine wave by default. After you use FM function, the modulation wave is sine wave by default. You can
change it with multi-functional control on interface for using frequency modulation or by pressing the relevant key for basic
waveform setting.
•
Square wave: duty ratio is 50%
•
Sawtooth wave: degree of symmetry is 0.10%
•
Arbitrary wave: when selecting arbitrary wave as modulation waveform, function/arbitrary waveform generator
limits length of arbitrary wave to 32Mpts by automatic test count.
2)
External source
When using an external modulation source, the modulation wave and frequency will be hidden in the parameter list when
an external waveform will be used to modulate carrier waveform. Frequency deviation of FM is controlled by ±5V signal
level on external analog modulation input terminal (Modulation In connector) on the back panel. Output frequency of FM is
more than carrier frequency at positive signal level and less than the latter at negative signal level. Lower external signal
level generates less deviation. For example, if frequency deviation in the parameter list is set to be 1kHz, output frequency
of FM is 1kHz more than the current carrier frequency when external modulation signal is +5V and 1kHz less than the
current carrier frequency when external modulation signal is -5V.
Set modulation wave frequency
The frequency of modulation wave can be set when an internal modulation source is used. After you use FM function, you
the frequency of the modulation wave is 100Hz by default. You can change it with the multi-functional control and direction
key on the interface for using frequency modulation or by pressing Freq. Modulation frequency range is 2mHz~200kHz.
When an external modulation source is used, modulation wave and frequency will be hidden in parameter list, when an
external waveform is used to modulate the carrier waveform. The frequency range of modulation signal of the external
input is 2mHz~20kHz.