Elenco Upgrade Kit SC100 to SC750 - Manual (Page 260)

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Now change to FFT mode to look at the frequency spectrums
corresponding to the 2 waveforms above. Try the settings shown
here.
Settings
This is the spectrum for the oscilloscope waveform shown on the
preceding page, which alternates between pulses and flat.
Because of the transition between pulses and flat, the spectrum is
the irregular shape shown here.
This is the spectrum for the oscilloscope waveform shown at the top
of this page, which has a continuous series of pulses. There are
only pulses there, with no transition between pulses and flat.
Hence the frequency spectrum is very “clean”, with the energy
concentrated at a few tall peaks instead of being spread out like in
the other spectrum display.
Project #PC19
Lasting Doorbell PC
OBJECTIVE: To look at the output of an alternately changing
circuit.