Instruction manual

HB 01-26-09 Oscilloscope (1) Lab 5 13
You will find that the two knobs labeled SWEEP TIME and MOD/DEPTH-SWEEP
RATE affect the waveform. Can you figure out exactly what these knobs do? Does it
make any difference whether these knobs are in or out? When you are finished, put the
frequency knob back in.
• MODULATION A “carrier (wave)” is a single frequency (sinusoidal) electromagnetic
wave. For radio broadcasting in the U.S. the carrier frequencies for AM stations lie
between 520 and 1610 kHz, and the carrier frequencies for FM stations lie between
87.5 and 108.0 MHz. Information, such as speech or music, has to be encoded on the
carrier wave. The process of encoding the information is called modulation. When
the amplitude of the carrier wave is varied it is called amplitude modulation or AM.
When the frequency of the carrier wave is varied it is called frequency modulation
or FM. Modulation at a single frequency corresponds to a pure tone. For example,
broadcasting “middle C” would require a sinusoidal modulation of about 261.6 Hz for
both AM and FM stations.
The output of the Wavetek function generator can be modulated at 400 Hz by an inter-
nally generated sine wave. The modulation can be either AM (amplitude modulation)
or FM (frequency modulation). To enable this function push the button marked MOD
ON. The knob marked MOD/DEPTH-SWEEP RATE controls whether the modula-
tion is AM (knob in) or FM (knob out). The amount of modulation is controlled by
rotating this knob. An output or “ carrier” frequency of about 10 kHz is suggested. Ob-
serve the modulated signal on the scope. Can you measure the period of the amplitude
modulation of this wave?
10 Finishing Up
Please leave the bench as you found it. Thank you.