BNC 645 - Manual (Page 48)

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both at the same time. The default source is internal, and the default
internal modulating waveform is sine wave. For internal source, one may
also choose from square with 50% duty cycle, URamp (Up or Positive
ramp with 100% symmetry), DRamp (Down or Negative ramp with 0%
symmetry), triangle (ramp with 50% symmetry), noise and arbitrary
waveforms. If an arbitrary waveform is chosen, the number of points in
the waveform is limited to 4k points with an automatic decimation
process. The default frequency for internal modulating waveform is 10Hz,
and the acceptable range is from 2 mHz to 20 kHz.
When external source is selected, the carrier waveform is modulated
with an external waveform present at the Modulation In connector on the
rear panel.
Phase Deviation
The phase deviation represents the peak variation in the phase of the
modulation output based on that of the carrier waveform. The range of
the phase deviation is from 0 to 360 degrees, and the default is 180
degrees.
When external source is selected as the source of modulating waveform,
the modulation is controlled by the specified phase deviation and the
±5v levels of the external waveform. When the external waveform is at
+5v, the output will reach positive maximum phase deviation; e.g.,
+180 degree phase shift if the specified phase deviation is 180 degrees.
When the external waveform is at -5v, the output will reach negative
maximum phase deviation; e.g., -180 degree phase shift if the specified
phase deviation is 180 degrees.
How to set up phase modulation
1. Press one of the following function buttons to choose your carrier
waveform: Sine, Square, Ramp, Arb. Specify all the necessary
waveform parameters for the carrier waveform as described in
Section 4.1, 4.2, 4.3 and 4.6.