User Manual LW120
4. Modulating waveform is sine waveform and modulating
frequency is 100 Hz.
NOTES
1. 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.
Frequency Modulating
Arbitrary Waveforms
In Examples 1 and 2 above, we showed you how to frequency
modulate standard waveforms. You can use these examples as
guideline for modulating arbitrary waveforms. Generating arbitrary
waveforms is discussed later in this chapter, so before you try
modulating such waveforms, make sure that you first familiarize
yourself with the arbitrary waveform generation techniques. In
general, arbitrary waveforms are made of waveform data and
sample clock. The rate of the sample clock determines the
frequency of the output waveform. For example, if your sample
clock is 1MS/s and your waveform segment is 1000 points long, the
frequency of the waveform is 1M / 1000 = 1 KHz.
The above example is somewhat oversimplified. What is important
to remember is that regardless if you are generating standard or
arbitrary waveforms, the FM function modulates the sample clock
and the parameters that you program for FM affects the SINE OUT
signal directly while the frequency characteristics for the front-panel
outputs must be computed.
FSK
In Frequency Shift Keying (FSK), the outputs of the LW120 hop
between two sample clock settings. You program the first sample
clock setting in the FREQUENCY menu and the shifted sample
clock frequency in the UTILITY menu. After you program the carrier
and the shifted frequencies, the instrument is ready to accept hop
commands. Hop control is done from the rear-panel FSK IN. This
input is level sensitive. When the FSK IN signal is low, the output
generates carrier sample clock, changing the level to high modifies
the output to shifted sample clock.
FSK is executed on the sample clock frequency. If you are just
using sine waveforms, then we recommend that you use the rear-
panel SINE OUT waveform. Using this output, the sample clock and
the shifted sample clock frequencies are used as nominal values. If
you want to use the FSK function from the front panel, then you
Using The Instrument 3-28