BNC 645 - Manual (Page 46)

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deviation is 100 kHz. When the external waveform is at -5v, the output
will reach negative maximum frequency deviation; e.g., 100 kHz
decrease from carrier frequency if the specified frequency deviation is
100 kHz.
How to set up frequency 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.
Figure 4-10
2. Press the Mod button to toggle on the modulation output.
3. Press the softkey under Type and press the softkey under FM to
select frequency modulation. A frequency modulation output will
be generated with the current parameters.
4. Press the softkey under Src to toggle between internal source (Int)
and external source (Ext) for selecting modulating waveform
source.
5. If internal source is selected:
a. Press the softkey under Shape to toggle between different
types of modulating waveform. If arbitrary waveform (Arb) is
selected as modulating signal source, the modulating signal
source is depending on the previous waveform selection in
arbitrary function. One may toggle the Mod key to see the
arbitrary modulating waveform message that temporarily
displayed on the screen.
b. Press the softkey under FM Freq and use numeric keypad or
the knob with the cursor keys to set the desired modulating
frequency.
6. Press the softkey under FreqDev to set the frequency deviation if
needed. Use numeric keypad or the knob with the cursor keys to
enter your value.