3-12 SIGNAL MODULATION The signal generator provides AM, FM, and square wave modulation
of the output signal. All modulation modes—AM, FM, and square
wave—can be active simultaneously.The following paragraphs provide
descriptions and operating instructions for each modulation mode. Use
the Amplitude Modulation Mode, Frequency Modulation Mode, and
Square WaveModulation Mode menu maps (Chapter 4, Figures 4-11,
4-12, and 4-13) to follow the menu sequences.
Amplitude
Modulation
Operating
Modes
The signal generator has two AM operation
modes—Linear AM and Log AM. In Linear AM
mode, sensitivity is continuously variable from 0%/V
to 100%/V.The amplitude of the RF output changes
linearly as the external AM input changes.
In Log AM mode, sensitivity is continuously vari-
able from 0 dB/V to 25 dB/V.The amplitude of the
RF output changes exponentially as the AM input
changes.
Providing
Amplitude
Modulation
Toprovide amplitude modulation, first set up the
external signal generator,then connect it to either
the 681XXC front or rear panel AM IN connector.
Next, press MODULATION. At the resulting menu
display,press AM . The right-most External AM
Status Menu (below) is displayed. Pressing “More”
bring up the left-most menu.
This menu contains an external AM status window
that shows the current menu selections and the
measured AM Depth. (The AM depth measurement
function measures the voltage of the external modu-
lation signal and calculates the percentage modula-
tion value.) This menu lets you perform the
following:
qTurnAM on and off.
qSelect the Linear AM or Log AM operating
mode.
qSet the AM Sensitivity
681XXC OM 3-73
LOCAL (FRONT SIGNAL
PANEL) OPERATION MODULATION