Chapter 2 Front Panel Operations  RIGOL 
DSG800 User Guide  2-17 
Frequency Modulation (FM) 
 
During frequency modulation (FM), the modulating signal changes the frequency of 
the RF carrier waveform.   
 
Press MOD  FM/ØM to enter the frequency/phase modulation parameter setting 
menu.   
 
To Turn on Frequency Modulation 
 
Press FM/ØM to select "FM" and then press Switch to select "On" or "Off".   
  On: turn on the FM function. The FM label in the function status area in the user 
interface is illuminated. 
  Off: turn off the FM function and this is the default state. 
 
Note: The frequency modulation and phase modulation cannot be turned on at the 
same time. In addition, if a sweep manner is selected and the step sweep time is 
lower than 200 ms, "You can turn on the FM or ØM when sweep time is greater than 
200ms" will be displayed in the user interface when frequency modulation is turned 
on. 
 
To Select the Modulation Source 
 
Press Source to select "Int" or "Ext" modulation source.   
 
1.  Internal Source 
When "Int" is selected, the internal modulation source is turned on. At this point, 
the instrument provides the modulating signal and you can set the modulation 
rate and modulation waveform of the modulating signal. 
 
2.  External Source 
When "Ext" is selected, Rate and Waveform are grayed out and disabled. The 
RF signal generator receives the external modulating signal input from the [EXT 
MOD IN] connector (as shown in the figure below) at the rear panel. This 
modulating signal can be any waveform. 
 
Note: The input amplitude of the external modulating signal cannot exceed 
+/-3 V (HighZ). To ensure the modulation performance, the input amplitude of 
the external modulating signal should be less than 1 Vpp. 
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