H4-57: FREQUENCY MODULATION BY FEEDBACK

ID Code: H4-57
Purpose: Demonstrate the effect on a wave form of frequency modulation using the wave to modulate itself.
Description: One of the components of an FM synthesizer is a voltage-controlled oscillator with feedback: the oscillator output is used as the FM modulator input. This is accomplished readily using one of the Wavetek voltage-controlled oscillators. This technique in fact produces a wave with a different shape and thus a different spectrum. The setup shows the wave shapes and spectra obtained by various modulation levels. For example, modulation of a sine wave by itself leads to the wave shape and spectrum shown in the photograph above. Using this technique a single oscillator with feedback can create a variety of wave shapes depending upon the level of feedback.

Start by setting the output at -10dB and change the fine control. Also try a square wave.

Availability: Available