Second Screen shot from Oscilloscope. This picture is very similar to the first one except that the curve rises to only one peak. The top of the peak is at the top of the screen, 4 divisions above zero. The peak is also somewhat rounded and wider than in the first picture. A legend on the screen informs us that the channel 1 vertical input is set to 700 millivolts per division. There are 3 lines on the screen which are known as cursors. A list superimposed on the screen gives the positions of the cursors. The Y1 cursor is set to a value of 1.95 volts. This is very close to being 3 dB down from the peak of the curve. See text. The two vertical lines that are cursors X1 and X2 intersect the curve at the point where the Y1 cursor crosses it. These lines mark the minus 3 dB points on the curve. The difference between these two cursors which is designated as delta X has a value of 42.4 milliseconds. How's that? The horizontal axis is frequency but the scope doesn't know it has been turned into a frequency response plotter. A scope plots time versus voltage and that's all it knows. Fortunately we are smarter than that. The time per division setting is 20 milliseconds per division but the sweep generator is set up to sweep 10 kHz in 20 ms. So if 20 ms equals 10 kHz then 42.4 ms equals 21.2 kHz. The 3 dB bandwidth is 21.2 kHz. This completes the verbal description.
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