9
Figure 9: carrier frequency with no A.M. modulation
Figure 10: 50 % Depth of an A.M. signal.
Frequency Modulation
Frequency modulation varies the frequency of the higher frequency carrier wave to convey the
frequency and amplitude of another lower frequency wave.
1. Set the signal generator to 1kHz and 1Vpp. Be sure the signal generator is in HIGH Z mode.
2. Press Autoset on the oscilloscope.
3. Press Shift -> FM on the signal generator.
4. The default FM frequency is 10Hz. The default F.M. Deviation is 100 Hz.
5. To see F.M. signals better we are going to use the FFT Button on the oscilloscope. Press FFT on
the oscilloscope and change the horizontal scale to 250Hz. The oscilloscope is working like a
spectrum analyzer in FFT mode. The horizontal represents frequency now, not time. You should
see a signal similar to figure 11.
6. Press Shift -> FM to turn the FM off. This is the carrier frequency with no frequency modulation.
7. Press Shift -> FM to turn the modulation back on. Change the oscilloscope horizontal scale to
1.25kHz. Press Shift -> Freq and enter 1 Hz. You should now see the carrier move back and forth
each second. How FAST
the frequency deviates conveys the frequency of the information, E.g.
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