User Manual LW120
Example 1, FSK Using
Standard Waveforms
This example will show how to generate FSK modulation using the
standard waveforms. The carrier frequency will be set to 1 MHz and
the shifted frequency to 1.5 MHz. We’ll monitor the FSK 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
1.000000MHz. 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 Sclk value and the number of points used for generating
the current waveform. In this case, the number of points is
computed from the relationship
N = Sclk/Freq = 64MS/1MHz = 64 points.
2. Now it becomes a bit tricky. When generating standard
waveforms, the Model LW120, depending on the output
frequency, automatically sets the number of points and their
associated sample clock. In FSK mode, only the sample clock
hops between frequencies, but the number of points remain
constant. This means that 64 waveform points will remain for
the carrier and for the shifted waveforms. From this statement
we can now compute the sample clock for the shifted frequency
using the following equation:
F = 64 Pts x 1.5 MHz = 96MS/s.
3. Press the UTILITY button
4. Select and press the Modulations option
5. Select and press the FSK option
6. Select the FSK State option
7. Rotate the dial clockwise to turn the FSK function ON
8. Select and press the Sclk2 parameter
9. Rotate the dial to adjust the Sclk2 parameter to 96 MS/s. This
value was selected using step 2 above.
10. Apply your FSK control signal to the trigger input
Using The Instrument 3-30