User Manual LW120
NOTE
If you selected Triggered mode for the LW120, you will
not be able to turn the FM function on. There are some
trigger modes that could be accessed through the FM
menu; These modes behave differently then the main
operating modes. For example, triggered FM means that
the output is actually in continuous mode but, every time
you trigger the LW120, a single FM cycle is initiated
hence the carrier frequency sweeps though the
deviation range and then idles at the carrier node.
Example 2, Modulating
Standard Waveforms
Using the Arbitrary FM
Mode
This example will show how to generate frequency modulation
using the standard waveforms and the Arbitrary FM Mode. The
output frequency will be set to 2 MHz, Deviation Range to 100 KHz
and 100 Hz sine as the modulating waveform. We’ll monitor the
frequency modulation from the front-panel outputs, then compare
the results to the rear-panel sine output connector.
1. Press the FREQUENCY button. Modify Freq to display
2.000000MHz. Observe and note that the Sclk parameter is
showing 64.00000MS/s. In standard waveform mode, the Sclk
parameter is set automatically by the instrument and can not be
modified directly. The information that we need from this display
is the number of points that the LW120 needs to generate 2
MHz. We can find this out from sclk/freq = 64/2 = 32 points. The
number 32 will be needed later to compute the deviation range
parameter.
2. Press the UTILITY button
3. Select and press the Modulations option
4. Select and press the FM option
5. Select the FM State option
6. Rotate the dial clockwise to turn the FM function ON
7. Select and press the ARB FM Type option. Note that only
parameter you can access is the FM Sclk. This parameter is
used for clocking the waveform memory that is used specifically
for the Arbitrary FM Mode. This sample clock parameter has no
effect on the main sample clock. The default value is 1 MS/s.
Note this value because it will be used for calculating the
frequency of the arbitrary wave that will be used as the
modulating waveform
Using The Instrument 3-25